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SiC–SiC matrix composite SiC–SiC composites have a relatively high thermal conductivity and can operate at very high temperatures due to their inherently high creep and oxidation resistance. Residual porosity and stoichiometry of the material can vary its thermal conductivity, with increasing porosity leading to lower thermal conductivity and presence of Si–O–C phase also leading to lower thermal conductivity. In general, a typical well processed SiC–SiC composite can achieve a thermal conductivity of around 30 W/m-K at 1000 Celsius. Since SiC–SiC composites are generally sought for in high temperature applications, their oxidation resistance is of high importance. The oxidation mechanism for SiC–SiC composites vary depending on the temperature range, with operation in the higher temperature range (>1000 °C) being more beneficial than at lower temperatures (<1000 °C). In the former case, passive oxidation generates a protective oxide layer wheres in the latter case, oxidation degrades the fiber-matrix interface. Nonetheless, oxidation is an issue and environmental barrier coatings are being investigated to address this issue. Silicon carbide (SiC) ceramic matrix composites (CMCs) are a specific application of engineering ceramic materials used to enhance aerospace applications such as turbine engine components and thermal protection systems. Due to exhibiting high temperature capabilities, low density, and resistance to oxidation and corrosion, SiC/SiC CMCs are largely used in aerospace applications | https://en.wikipedia.org/wiki?curid=39516879 |
SiC–SiC matrix composite The use of SiC/SiC CMCs on rotating engine components reduce the complexity of design and engine structure weight, providing improved performance and fuel emissions. The implementation of SiC/SiC ceramic matrix components will improve aircraft and space vehicle performance and fuel efficiency, reducing additional harm to the environment in a cost-effective manner. Additional applications of SiC/SiC CMCs include combustion and turbine section components of aero-propulsion and land-based gas turbine engines, thermal protection systems, thruster nozzles, reusable rocket nozzles, and turbopump components for space vehicles. With the development and implementation of future SiC/SiC CMCs, the SiC fiber creep and rupture properties must be examined. Defects such as grain size, impurities, porosity, and surface toughness all contribute to SiC fiber creep and rupture. Due to relatively low toughness, low damage tolerance, and large variability in mechanical properties, CMCs have been limited to less critical components. In the future, the implementation of greater SiC/SiC CMCs into aerospace applications is hindered by lack of understanding of ceramic material characteristics, degradation, mechanisms, and interactions to prevent component life and broaden component design. | https://en.wikipedia.org/wiki?curid=39516879 |
William Klyne William "Bill" Klyne (March 23, 1913, in Enfield, Middlesex – November 13, 1977) was an organic chemist known for his work in steroids and stereochemistry — a field in which he was a "pioneer", and in which Ernest Eliel and Norman Allinger described him as "one of the world's experts". Klyne taught at Westfield College, University of London, where he served as dean of science from 1971 to 1973, and as vice-principal from 1973 to 1976. He also served on the editorial board of the Biochemical Society from 1950 to 1955, and on IUPAC's nomenclature committee from 1971 until his death. As well, he established and maintained the Medical Research Council's Steroid Reference Collection, and wrote several textbooks, including "The Chemistry of Steroids" (1957) and "Atlas of Stereochemical Correlations" (1974). Klyne met Barbara Clayton in 1947 while both were employed at the Medical Research Council; they married in 1949. | https://en.wikipedia.org/wiki?curid=39520456 |
A. A. Griffith Medal and Prize The is awarded annually by the Institute of Materials, Minerals and Mining in commemoration of Alan Arnold Griffith. The award was established by the Materials Science Club of Great Britain in 1965, two years after its formation in 1963. Modern materials science as an integrated discipline (as distinct from single-material studies such as metallurgy) was in its infancy, and the Materials Science Club was a 'gathering place' for this new field of applied science. In 1985 it was merged into the Institute of Metals, which in turn became part of the Institute of Materials, Minerals and Mining. The is given in recognition of distinguished work that has made or is making a notable contribution to any branch of materials science. The prize value is £300. | https://en.wikipedia.org/wiki?curid=39520773 |
Polycarbonyl Polycarbonyl, (also known as polymeric-CO, p-CO or poly-CO) is a solid metastable and explosive polymer of carbon monoxide. The polymer is produced by exposing carbon monoxide to high pressures. The structure of the solid appears amorphous, but may include a zig zag of equally spaced CO groups. Poly-CO can be produced at pressures of 5.2 GPa. Polymerisation is catalysed by blue light at slightly lower pressures in the δ-phase of solid CO. Another white phase can be made at higher temperatures at 6 or 7 GPa. Poly-CO appears to be a yellow to dark red amorphous phase. Whereas the white phase appears to be crystalline. R. J. Mills discovered this solid, which was first produced in a tungsten carbide anvil in 1947. Originally this was thought to be polymeric carbon suboxide, but the formation does not yield any gas byproduct such as carbon dioxide. The yield of the solid can be up to 95%. The polymer is stable above about 80K. Below this temperature the ε form of solid molecular CO is formed instead. When the pressure is released the polymer remains stable at atmospheric pressure. The solid dissolves in water, alcohol and acetone. When exposed to the atmosphere it is hygroscopic, becomes gluey, and changes colour, becoming darker. The reaction with water produces carboxylic groups. The solid stores a high energy. It can decompose explosively forming glassy carbon and carbon dioxide. The energy density stored can be up to 8 kJ/g. During the decomposition the temperature can be 2500K. The density is 1 | https://en.wikipedia.org/wiki?curid=39528525 |
Polycarbonyl 65 gcm, however most of the solid produced is porous, so the true density is likely to be higher. Infrared spectroscopy shows bands at 650, 1210, 1440, 1650 and 1760 cm. The 1760 band is likely to be due to the -C-(C=O)-C- structure. The 1600 is due to vibration of a C=C double bond. The solid is electrically insulating with an electronic gap energy of 1.9 eV. Nuclear magnetic resonance for the material made from CO shows sharp resonance at 223 ppm due to ester or lactone attached carbon, and 151 ppm due to C=C double bonds. There is also broad resonance at 109 and 189 ppm. Over time of a few days, the 223 ppm peak reduces and all the other features increase in strength. Ideas of the structure include a zig zag chain of CO pointing in opposite directions, or five atom rings connected by CO and C-C bonds. The rings are lactones of tetronic acid: -C:-(C=O)-(C-O-)-(C=O)-O-. Interconnections between the rings are zig zags of CO. Other ideas of the structure of the solid, include graphitic carbon with carbon dioxide under pressure, and a polymer with this CO monomer: -(C=O)-O-(C-)=C<. Yet other ideas are that the solid is the same as the polymer of carbon suboxide with oxalic anhydride. | https://en.wikipedia.org/wiki?curid=39528525 |
2-Pyridone (data page) This page provides supplementary chemical data on 2-pyridone. H-NMR (400 MHz, CDOD): /ρ = 8.07 (dd,J = 2.5 Hz,J = 1.1 Hz, 1H, C-6), 7.98 (dd,J = 4.0 Hz,J = 2.0 Hz, 1H, C-3), 7.23 (dd,J = 2.5 Hz,J = 2.0 Hz, 1H, C-5), 7.21 (dd,J = 4.0 Hz,J = 1.0 Hz, 1H, C-4). (MeOH):ν (lg ε) = 226.2 (0.44), 297.6 (0.30). (KBr): ν = 3440 cm–1 (br, m), 3119 (m), 3072 (m), 2986 (m), 1682 (s), 1649 (vs), 1609 (vs), 1578 (vs), 1540 (s), 1456 (m), 1433 (m), 1364 (w), 1243 (m), 1156 (m), 1098 (m), 983 (m), 926 (w), 781 (s), 730 (w), 612 (w), 560 (w), 554 (w), 526 (m), 476 (m), 451 (w). EI-MS (70 eV): m/z (%) = 95 (100) [M], 67 (35) [M - CO], 51 (4)[CH]. | https://en.wikipedia.org/wiki?curid=39528627 |
EcoLon Ecolon may refer either to recycled (ecologically-friendly nylon) mineral-glass reinforced Nylon 6 (Perlon) engineering resins, or to a ceramic filled fused silica coating commonly used in cookware (Ecolon). Ecolon cookware coatings are touted as highly resistant to scratches caused by utensils, metallic cleaning pads and abrasives, and withstand high temperatures, leading to great durability. Teflon coatings start breaking down at 240 °C, while Ecolon remains stable up to 450 °C. engineering resin is produced by Wellman Engineering Resins. Ecolon ceramic coatings are a trademark of Neoflam. | https://en.wikipedia.org/wiki?curid=39529197 |
Biochemical Predestination is a 1969 book by Dean H. Kenyon and Gary Steinman which argued in support of biochemical evolution. In the book, Kenyon and Steinman conclude that "Life might have been biochemically predestined by the properties of attraction that exist between its chemical parts, especially between amino acids in proteins." They argued that life originated with the chemical properties of amino acids causing them to be attracted to each other, forming long protein chains, most important in every living cell. Kenyon believed that proteins were directly formed by attraction between amino acids without DNA coding, and that these were derivatives from non-living raw chemicals in a conducive environment. In 1976 Kenyon was persuaded by the young Earth creationist arguments of A. E. Wilder-Smith. In the 1982 foreword he wrote to "What Is Creation Science?" by Henry M. Morris and Gary Parker, Kenyon said that he no longer accepted the pro-evolution arguments in "Biochemical Predestination". At the "Edwards v. Aguillard" trial he provided an affidavit in support of creation science and noted the book as one of his publications. Kenyon subsequently became a co-author of "Of Pandas and People" which rebranded creation science as intelligent design | https://en.wikipedia.org/wiki?curid=39530033 |
Biochemical Predestination The theory propounded was summarized by Stephen Berry, a chemist; "describing the following causal chain: the properties of the chemical elements dictate the types of monomers that can be formed in prebiotic syntheses, which then dictate the properties of the occurring polymers, which finally dictate the properties of the first eobionts and all succeeding cells." Kenyon's work was about virus production. Intelligent design proponent Stephen C. Meyer says that the book provided a new approach which came to be known as "Self-organization". Kenyon began to doubt his theory in the mid-1970s after a student posed the question to him as to how the first proteins could have been assembled without specific genetic instructions. On a fellowship at the Graduate Theological Union in Berkeley during the 1969-1970 academic year, he reviewed literature on the relationship of science and religion. He began to rethink his Christian faith, and explored the topic further in a 1974 sabbatical at the University of Oxford. In 1976, a student gave him a book by the young Earth creationist A. E. Wilder-Smith, and "Eventually, several other books and articles by neo-creationists came to my attention. I read some of Henry Morris’ books, in particular, "The Genesis Flood". I’m not a geologist, and I don’t agree with everything in that book, but what stood out was that here was a scientific statement giving a very different view of earth history | https://en.wikipedia.org/wiki?curid=39530033 |
Biochemical Predestination Though the book doesn’t deal with the subject of the origin of life per se, it had the effect of suggesting that it is possible to have a rational alternative explanation of the past." In 1976 he wrote a new section for Morris and Whitcomb's "". In the 1982 foreword he wrote to "What Is Creation Science?" by Morris and Gary Parker, Kenyon said that he no longer accepted the pro-evolution arguments in "Biochemical Predestination". At the "Edwards v. Aguillard" trial he provided an affidavit in support of creation science and noted the book as one of his publications. Kenyon subsequently became a co-author of "Of Pandas and People" which rebranded creation science as intelligent design. | https://en.wikipedia.org/wiki?curid=39530033 |
European green infrastructure The is an important part of the new (post-2010) EU strategy for biodiversity and biodiversity policy. It is one of the main tools to tackle threats on biodiversity resulting from habitat fragmentation, land use change and loss of habitats. Green Infrastructure will play a decisive role in integrating biodiversity into other policies, such as agriculture, forestry, water, marine and fisheries, regional and cohesion policy, climate change mitigation and adaptation, transport, energy and land use policy. It is also an important tool for existing Directives such as the Water Framework Directive, the Marine Framework Directive, Environmental Impact Assessment and Strategic Environment Assessment Directives. In addition, particular attention will be given to strengthening the integration of green infrastructure aspects in the EU’s various funding programmes (e.g. structural and cohesion funds, CAP, LIFE) over the current and future financial programming period starting in 2013 and to improving the ecological coherence of the Natura 2000 Network. The continued development of Geographic Information Systems (GIS) and their increasing level of use is particularly important in the development of Green Infrastructure plans. The plans frequently are based on GIS analysis of many layers of geographic information. | https://en.wikipedia.org/wiki?curid=39533411 |
Free-flow electrophoresis (FFE), also known as carrier-free electrophoresis, is a matrix-free electrophoretic separation technique. FFE is an analogous technique to capillary electrophoresis, with a comparable resolution, that can used for scientific questions, where semi-preparative and preparative amounts of samples are needed. It is used to quantitatively separate samples according to differences in charge or isoelectric point. Because of the versatility of the technique, a wide range of protocols for the separation of samples like rare metal ions, protein isoforms, multiprotein complexes, peptides, organelles, cells, DNA origami, blood serum and nanoparticles exist. The advantage of FFE is the fast and gentle separation of samples dissolved in a liquid solvent without any need of a matrix, like polyacrylamide in gel electrophoresis. This ensures a very high recovery rate since analytes do not adhere to any carrier or matrix structure. Because of its continuous nature and high volume throughput, this technique allows a fast separation of preparative amounts of samples with a very high resolution. Furthermore, the separations can be conducted under native or denaturing conditions. FFE was developed in the 1960s by Kurt Hannig at the Max-Planck-Institute in Germany. Until the 1980s, it was a standardized technology for the separation of cells and organelles, and FFE was even tested in space to minimize the sedimentation under zero gravity | https://en.wikipedia.org/wiki?curid=39537386 |
Free-flow electrophoresis As flow cytometry became the standard method for cell sorting, FFE developments focused on the separation of proteins and charged particles. Some groups are also working on miniaturized versions of FFE systems or micro FFEs. The separation chamber consists of a backplate and a front plate. The backplate usually consists of a cooled aluminum block, covered with a plastic covered glass mirror. The front plate is nowadays made of PMMA, in earlier times glass has been used. The distance between the front- and the backplate can be adjusted by spacers and is usually between 0.1 - 0.5 mm. The front plate also contains the inlets for the separation buffers and the sample, the outlets for the fractionation tubes and the platinum wires as electrodes. By applying different buffers over the multiple buffer inlets the operator is able to change pH, salt concentrations or composition and therefore the separation conditions over the width of the chamber. The separation buffers and the sample are applied by peristaltic pumps, to ensure a laminar flow. A high voltage electric field is applied perpendicular to the laminar flow. Analytes in the laminar flow can be separated by charge density and/or isoelectric point. Because of its highly versatile nature, this technique can make use of different modes of electrophoresis, like for example isotachophoresis, isoelectric focusing or (interval) zone electrophoresis | https://en.wikipedia.org/wiki?curid=39537386 |
Free-flow electrophoresis At the end of the separation cell, the separated sample is split up at the fractionation tubes and collected in microtiter plates. Afterwards the samples can be characterized by all major techniques like HPLC, LC-MS, mass spectrometry (ESI / MALDI, depending on the protocol used) or electrophoresis (IEF / SDS PAGE, 2D-PAGE). Standard application include the high-resolution separation of protein complexes, membrane proteins, protein and antibody isoforms, cells, subcellular compartments (like organelles, ribosomes) and liposomes. By making use of very flat pH-gradients, generated by ampholytes, it is possible to separate protein isoforms, that vary by less than 0.02 pH units, with a throughput of around 3 mg/h. It is also possible to add additives to the buffers, to increase the resolution or denature the samples. Typically concentrations of urea up to 8M, 0.1-1% of detergents like: CHAPS, CHAPSO, Digitonin, Dodecyl-ß-D-maltoside, Octyl-ß-D-glucoside, Triton-X-114 (IEF) and DTT up to 50 mM are tolerated. | https://en.wikipedia.org/wiki?curid=39537386 |
Sophorolipid A sophorolipid is a surface-active glycolipid compound that can be synthesized by a selected number of non-pathogenic yeast species.<ref </ref> They are potential bio-surfactants due to their biodegradability and low eco-toxicity. Sophorolipids are glycolipids consist of a hydrophobic fatty acid tail of 16 or 18 carbon atoms and a hydrophilic carbohydrate head sophorose, a glucose-derived di-saccharide with an unusual β-1,2 bond and can be acetylated on the 6′- and/or 6′′- positions. One terminal or sub terminal hydroxylated fatty acid is β-glycosidically linked to the sophorose module. The carboxylic end of this fatty acid is either free (acidic or open form) or internally esterified at the 4′′ or in some rare cases at the 6′- or 6′′-position (lactonic form). The physicochemical and biological properties of sophorolipids are significantly influenced by the distribution of the lactone vs. acidic forms produced in the fermentative broth. In general, lactone sophorolipids are more efficient in reducing surface tension and are better antimicrobial agents, whereas acidic sophorolipids display better foaming properties. Acetyl groups can also lower the hydrophilicity of sophorolipids and enhance their antiviral and cytokine stimulating effects. Sophorolipids are produced by various non pathogenic yeast species such as "Candida apicola", "Rhodotorula bogoriensis", "Wickerhamiella domercqiae", and "Starmerella bombicola" | https://en.wikipedia.org/wiki?curid=39564606 |
Sophorolipid Recent research has meant sophorolipids can be recovered during a fermentation using a gravity separator in a loop with the bioreactor, enabling the production of >770 g/l sophorolipid at a productivity 4.24 g/l/h, some of the highest values seen in a fermentation process Desirable properties of biosurfactants are biodegradability and low toxicity. Sophorolipids produced by several yeasts belonging to "candida" and the "starmerella" clade, and Rhamnolipid produced by "Pseudomonas aeruginosa" etc. Besides biodegradibility, low toxicity, and high production potential, sophorolipids have a high surface and interfacial activity. Sophorolipids are reported to lower surface tension (ST) of water from 72 to 30-35 mN/m and the interfacial tension (IT) water/hexadecane from 40 to 1 mN/m. In addition to this, sophorolipids are reported to function under wide ranges of temperatures, pressures and ionic strengths; and they also possess a number of other useful biological activities including Antimicrobial, virucidal, Anticancer, Immuno-modulatory properties. A detailed and comprehensive literature review on the various aspects of sophorolipids production (e.g. producing micro-organisms, bio-synthetic pathway, effect of medium components and other fermentation conditions and downstream process of sophorolipids is available in the published work of Van Bogaert et al | https://en.wikipedia.org/wiki?curid=39564606 |
Sophorolipid This work also discusses potential application of sophorolipids (and their derivatives) as well as the potential for genetic engineering strains to enhance sophorolipid yields. Researchers have focused on optimization of sophorolipid production in submerged fermentation, but some efforts have also investigated the possibility of sophorololipid production using solid state fermentation (SSF). The production process can be significantly impacted by the specific properties of the carbon and oil substrates used; and several inexpensive alternatives to more traditional substrates have been investigated. These potential substrates include: biodiesel by-product streams, waste frying oil, restaurant waste oil, industrial fatty acid residues, mango seed fat, and soybean dark oil. The use of most of these substrates have resulted in lower yields compared to traditional fermentation substrates. To enhance the performance of surfactant properties of natural sophorolipids, chemical modification methods have been actively pursued. Recently, researchers demonstrated the possibility of applying sophorolipids as building blocks via ring-opening metathesis polymerization for a new type of polymers, known as polysophorolipids which show promising potentials in biomaterials applications. | https://en.wikipedia.org/wiki?curid=39564606 |
Alizarine yellow may refer to: | https://en.wikipedia.org/wiki?curid=39568548 |
Oxygen compatibility is the issue of compatibility of materials for service in high concentrations of oxygen. It is a critical issue in space, aircraft, medical, underwater diving and industrial applications. Aspects include effects of increased oxygen concentration on the ignition and burning of materials and components exposed to these concentrations in service. Understanding of fire hazards is necessary when designing, operating, and maintaining oxygen systems so that fires can be prevented. Ignition risks can be minimized by controlling heat sources and using materials that will not ignite or will not support burning in the applicable environment. Some materials are more susceptible to ignition in oxygen-rich environments, and compatibility should be assessed before a component is introduced into an oxygen system. Both pertial pressure and concentration of oxygen affect the fire hazard. The issues of cleaning and design are closely related to the compatibility of materials for safety and durability in oxygen service. Fires occur when oxygen, fuel, and heat energy combine in a self-sustaining chemical reaction. In an oxygen system the presence of oxygen is implied, and in a sufficiently high partial pressure of oxygen, most materials can be considered fuel. Potential ignition sources are present in almost all oxygen systems, but fire hazards can be mitigated by controlling the risk factors associated with the oxygen, fuel, or heat, which can limit the tendency for a chemical reaction to occur | https://en.wikipedia.org/wiki?curid=39574992 |
Oxygen compatibility Materials are easier to ignite and burn more readily as oxygen pressure or concentration increase. so operating oxygen systems at the lowest practicable pressure and concentration may be enough to avoid ignition and burning. Use of materials which are inherently more difficult to ignite or are resistant to sustained burning, or which release less energy when they burn, can, in some cases, eliminate the possibility of fire or minimize the damage caused by a fire. Although heat sources may be inherent in the operation of an oxygen system, initiation of the chemical reaction between the system materials and oxygen can be limited by controlling the ability of those heat sources to cause ignition. Design features which can limit or dissipate the heat generated to keep temperatures below the ignition temperatures of the system materials will prevent ignition. An oxygen system should also be protected from external heat sources. The process of assessment of oxygen compatibility would generally include the following stages: Compatibility analysis would also consider the history of use of the component or material in similar conditions, or of a similar component. Oxygen service implies use in contact with high partial pressures of oxygen. Generally this is taken to mean a higher partial pressure than possible from compressed air, but also can occur at lower pressures when the concentration is high | https://en.wikipedia.org/wiki?curid=39574992 |
Oxygen compatibility Oxygen cleaning is preparation for oxygen service by ensuring that the surfaces that may come into contact with high partial pressures of oxygen while in use are free of contaminants that increase the risk of ignition. Oxygen cleaning is a necessary, but not always a sufficient condition for high partial pressure or high concentration oxygen service. The materials used must also be oxygen compatible at all expected service conditions. Aluminium and titanium components are specifically not suitable for oxygen service. In the case of diving equipment, oxygen cleaning generally involves the stripping down of the equipment into individual components which are then thoroughly cleaned of hydrocarbon and other combustible contaminants using non-flammable, non-toxic cleaners. Once dry, the equipment is reasssembled under clean conditions. Lubricants are replaced by specifically oxygen- compatible substitutes during reassembly. The standard and requirements for oxygen cleaning of diving apparatus varies depending on the application and applicable legislation and codes of practice. For scuba equipment, the industry standard is that breathing apparatus which will be exposed to concentrations in excess of 40% oxygen by volume should be oxygen cleaned before being put into such service. Surface supplied equipment may be subject to more stringent requirements, as the diver may not be able to remove the equipment in an accident | https://en.wikipedia.org/wiki?curid=39574992 |
Oxygen compatibility Oxygen cleaning may be required for concentrations as low as 23% Cleaning agents used range from heavy-duty industrial solvents and detergents such as liquid freon, trichlorethylene and anhydrous trisodium phosphate, followed by rinsing in deionised water. These materials are now generally deprecated as being environmentally unsound and an unnecessary health hazard. Some strong all-purpose household detergents have been found to do the job adequately. They are diluted with water before use, and used hot for maximum efficacy. Ultrasonic agitation, shaking, pressure spraying and tumbling using glass or stainless steel beads or mild ceramic abrasives are effectively used to speed up the process where appropriate. Thorough rinsing and drying is necessary to ensure that the equipment is not contaminated by the cleaning agent. Rinsing should continue until the rinse water is clear and does not form a persistent foam when shaken. Drying using heated gas – usually hot air – is common and speeds up the process. Use of a low oxygen fraction drying gas can reduce flash-rusting of the interior of steel cylinders. After cleaning and drying, and before reassembly, the cleaned surfaces are inspected and where appropriate, tested for the presence of contaminants. Inspection under ultraviolet illumination can show the presence of fluorescent contaminants, but is not guaranteed to show all contaminants | https://en.wikipedia.org/wiki?curid=39574992 |
Oxygen compatibility Design for oxygen service includes several aspects: As a general rule, oxygen compatibility is associated with a high ignition temperature, and a low rate of reaction once ignited. Organic materials generally have lower ignition temperatures than metals considered suitable for oxygen service. Therefore the use of organic materials in contact with oxygen should be avoided or minimised, particularly when the material is directly exposed to gas flow. When an organic material must be used for parts such as diaphragms, seals, packing or valve seats, the material with the highest ignition temperature for the required mechanical properties is usually chosen. Fluoroelastomers are preferred where large areas are in direct contact with oxygen flow. Other materials may be acceptable for static seals where the flow does not come into direct contact with the component. Only tested and certified oxygen compatible lubricants and sealants should be used, and in as small quantities as is reasonably practicable for effective function. Projection of excess sealant or contamination by lubricant into flow regions should be avoided. Commonly used engineering metals with a high resistance to ignition in oxygen include copper, copper alloys, and nickel-copper alloys, and these metals also do not normally propagate combustion, making them generally suitable for oxygen service | https://en.wikipedia.org/wiki?curid=39574992 |
Oxygen compatibility They are also available in free-cutting, castable or highly ductile alloys, and are reasonably strong, so are useful for a wide range of components for oxygen service. Aluminium alloys have a relatively low ignition temperature, and release a large amount of heat during combustion and are not considered suitable for oxygen service where they will be directly exposed to flow, but are acceptable for storage cylinders where the flow rate and temperatures are low. Hazards analyses are performed on materials, components, and systems; and failure analyses determine the cause of fires. Results are used in design and operation of safe oxygen systems. | https://en.wikipedia.org/wiki?curid=39574992 |
C5H8N2O3 The molecular formula CHNO (molar mass: 144.130 g/mol) may refer to: | https://en.wikipedia.org/wiki?curid=39575959 |
Graphite-like ZnO nanostructures Most of the synthesized Zinc oxide (ZnO) nanostructures in different geometric configurations such as nanowires, nanorods, nanobelts and nanosheets are usually in the wurtzite crystal structure. However, it was found from density functional theory calculations that for ultra-thin films of ZnO, the graphite-like structure was energetically more favourable as compared to the wurtzite structure. The stability of this phase transformation of wurtzite lattice to graphite-like structure of the ZnO film is only limited to the thickness of about several Zn-O layers and was subsequently verified by experiment. Similar phase transition was also observed in ZnO nanowire when it was subjected to uniaxial tensile loading. However, with the use of the first-principles all electron full-potential method, it was observed that the wurtzite to graphite-like phase transformation for ultra-thin ZnO films will not occur in the presence of a significant amount of oxygen vacancies (V) at the Zn-terminated (0001) surface of the thin film. The absence of the structural phase transformation was explained in terms of the Coulomb attraction at the surfaces. The graphitic ZnO thin films are structurally similar to the multilayer of graphite and are expected to have interesting mechanical and electronic properties for potential nanoscale applications | https://en.wikipedia.org/wiki?curid=39586666 |
Graphite-like ZnO nanostructures In addition, density functional theory calculations and experimental observations also indicate that the concentration of the V is the highest near the surfaces as compared to the inner parts of the nanostructures. This is due to the lower V defect formation energies in the interior of the nanostructures as compared to their surfaces. | https://en.wikipedia.org/wiki?curid=39586666 |
Mary Elvira Weeks (April 10, 1892, Lyons, Wisconsin– June 20, 1975, Detroit, Michigan) was an American chemist and historian of science. Weeks was the first woman to receive a Ph.D. in chemistry and the first woman to be a faculty member at the University of Kansas. Her book "Discovery of the Elements" is considered the "first connected narrative of how scientists unraveled the mysteries of matter" and a "Classic of chemistry". It went through seven editions and was published in multiple languages. Weeks also published "A History of the American Chemical Society" (1952) with Charles Albert Browne, completing it after his death in 1947. In 1913 Weeks earned a bachelor's in chemistry from Ripon College where she worked with Albert F. Gilman. In 1914 she received a master's degree from the University of Wisconsin–Madison, where she worked with Joseph Howard Mathews. For seven years (1914-1921), Weeks worked as a high school teacher and chemical technician. In 1921, she took a job as a college instructor, teaching quantitative analysis at the University of Kansas while continuing to study. She completed her Ph.D. at the University of Kansas in 1927, writing a thesis on "The role of hydrogen ion concentration in the precipitation of calcium and magnesium." Once she had her Ph.D. Weeks became an assistant professor and in 1937, an associate professor. She remained in Kansas for 22 years, carrying a heavy teaching load and doing a limited amount of laboratory research | https://en.wikipedia.org/wiki?curid=39587373 |
Mary Elvira Weeks Her research tended to be in the areas of physical and analytic chemistry. While in Kansas, she began researching and writing about the history of chemistry, and published "Discovery of the Elements" (1933). In 1944, Weeks left Kansas to become a research librarian at the Kresge-Hooker Science Library of Wayne State University in Detroit, Michigan. There she became head of the translation department. Weeks retired from Wayne State in 1954 and continued to live in Detroit. Weeks continued to be active as a translator and as an editor after her retirement, working with the "Record of Chemical Progress" (?-1971) and "Chymia" (1956-1967). Weeks was a member of the American Chemical Society, the American Association for Advancement of Science, the History of Science Society, the Special Libraries Association, the Swedish History of Science Society, Phi Beta Kappa, and Sigma Xi. Because her interests leaned to the humanities, Weeks was drawn to the history of chemistry. Initially, she wrote about the elements as a hobby. From 1932-1933, while at the University of Kansas, Weeks wrote a series of 21 articles on the discovery of the elements for the "Journal of Chemical Education". Due to demand for reprints, the articles were collected and published in book form in 1933. "Discovery of the Elements" went through multiple editions. Both book and the earlier articles were liberally illustrated with pictures of chemists from the collection of Frank B. Dains, an older Kansas colleague of Weeks | https://en.wikipedia.org/wiki?curid=39587373 |
Mary Elvira Weeks By 1968, "Discovery of the Elements" had appeared in seven editions, and had been updated to include the 94 elements that were discovered between 1524 and 1964. Editions included a wartime release in limited numbers due to restrictions on use of paper. The book had been translated into multiple languages. Weeks, who spoke French, German, Italian, Japanese, Spanish, Swedish, and Russian, focused on translation for much of her time at Wayne State University. The seventh edition was identifed as a "Classic of chemistry". It was hailed as "a new edition of an old favorite", a "definitive and unique work" whose "value is well established and recognized by all." Revised by Weeks and Henry M. Leicester, it contained 2,688 references and 373 illustrations. Her work was one of the inspirations for "The Lost Elements: The Periodic Table's Shadow Side" (2015). In 1946 or 1947, Weeks began collaborating with Charles A. Browne on a retrospective history of the American Chemical Society. Browne was responsible for the structure of the project and the first nine chapters. After Browne's death in 1947, Weeks brought the project to completion. "A History of the American Chemical Society—Seventy-five Eventful Years" was published in 1952. It was welcomed as avoiding the pitfalls common to commissioned histories. In 1967, Weeks won the Dexter Award for Outstanding Achievement in the History of Chemistry from the American Chemical Society. | https://en.wikipedia.org/wiki?curid=39587373 |
Alkaline water electrolysis has a long history in the chemical industry. It is a type of electrolyzer that is characterized by having two electrodes operating in a liquid alkaline electrolyte solution of potassium hydroxide (KOH) or sodium hydroxide (NaOH). These electrodes are separated by a diaphragm, separating the product gases and transporting the hydroxide ions (OH) from one electrode to the other. A recent comparison showed that state-of-the-art nickel based water electrolyzers with alkaline electrolytes lead to competitive or even better efficiencies than acidic polymer electrolyte membrane water electrolysis with platinum group metal based electrocatalysts. Electrolysis requires minerals to be present in solution. Tap, well, and ground water contains various minerals, some of which are alkaline while others are acidic. Water above a pH of 7.0 is considered alkaline; below 7.0 it is acidic. The requirement is that there must be ions in the water to conduct electricity for the water electrolysis process to occur. The electrodes are typically separated by a thin porous foil (with a thickness between 0.050 to 0.5 mm), commonly referred to as diaphragm or separator. The diaphragm is non-conductive to electrons, thus avoiding electrical shorts between the electrodes while allowing small distances between the electrodes. The ionic conductivity is supplied by the aqueous alkaline solution, which penetrates in the pores of the diaphragm. The state-of-the-art diaphragm is Zirfon, a composite material of zirconia and Polysulfone | https://en.wikipedia.org/wiki?curid=39592391 |
Alkaline water electrolysis The diaphragm further avoids the mixing of the produced hydrogen and oxygen at the cathode and anode, respectively. Typically, Nickel based metals are used as the electrodes for alkaline water electrolysis. Considering pure metals, Ni is the most active non-noble metal. The high price of good noble metal electrocatalysts such as platinum group metals and their dissolution during the oxygen evolution is a drawback. Ni is considered as more stable during the oxygen evolution. But, stainless steel has shown good stability and better catalytic activity than Ni at high temperatures during the Oxygen Evolution Reaction (OER). High surface area Ni catalysts can be achieved by dealloying of Nickel-Zinc or Nickel-Aluminium alloys in alkaline solution, commonly referred to as Raney Nickel. In cell tests the best performing electrodes thus far reported consisted of plasma vacuum sprayed Ni alloys on Ni meshes and hot dip galvanized Ni meshes. The latter approach might be interesting for large scale industrial manufacturing as it is cheap and easily scalable. In comparison to polymer electrolyte water electrolysis, the advantages of alkaline water electrolysis are mainly: | https://en.wikipedia.org/wiki?curid=39592391 |
Spherical surface acoustic wave (SAW) sensor Spherical surface acoustic wave sensors use a type of surface acoustic wave (SAW) that travels along the surface of a medium exhibiting elasticity with exponentially decaying amplitude along depth. MEMS-IDT technology allows the use of SAW waves to sense various gases. Sensitivity up to 10 ppm of hydrogen using a spherical Ball SAW device is obtained. Conventional planar SAW sensors are based on principle that the parameters such as amplitude, speed and phase of Surface acoustic wave changes on adsorption of gas molecules. Limitation of planar SAW based sensors is that the change in above mentioned parameters is very small due to limited path offered to Surface acoustic wave by planar sensor. In case of Spherical sensors surface acoustic wave make several round trips along the equator of a ball as shown in fig, which offer longer paths to Surface acoustic wave hence even smaller change in parameters is amplified with multiple turns, which increases the sensitivity of the sensor considerably. | https://en.wikipedia.org/wiki?curid=39594285 |
C9H9NO4 The molecular formula CHNO may refer to: | https://en.wikipedia.org/wiki?curid=39608703 |
Hafnium tetrafluoride is the inorganic compound with the formula HfF. It is a white solid. It adopts the same structure as zirconium tetrafluoride, with 8-coordinate Hf(IV) centers. | https://en.wikipedia.org/wiki?curid=39612594 |
Hydrogel encapsulation of quantum dots The behavior of quantum dots (QDs) in solution and their interaction with other surfaces is of great importance to biological and industrial applications, such as optical displays, animal tagging, anti-counterfeiting dyes and paints, chemical sensing, and fluorescent tagging. However, unmodified quantum dots tend to be hydrophobic, which precludes their use in stable, water-based colloids. Furthermore, because the ratio of surface area to volume in a quantum dot is much higher than for larger particles, the thermodynamic free energy associated with dangling bonds on the surface is sufficient to impede the quantum confinement of excitons. Once solubilized by encapsulation in either a hydrophobic interior micelle or a hydrophilic exterior micelle, the QDs can be successfully introduced into an aqueous medium, in which they form an extended hydrogel network. In this form, quantum dots can be utilized in several applications that benefit from their unique properties, such as medical imaging and thermal destruction of malignant cancers. Quantum dots (QDs) are nano-scale semiconductor particles on the order of 2-10 nm in diameter. They possess electrical properties between those of bulk semi-conductors and individual molecules, as well as optical characteristics that make them suitable for applications where fluorescence is desirable, such as medical imaging. Most QDs synthesized for medical imaging are in the form of CdSe(ZnS) core(shell) particles | https://en.wikipedia.org/wiki?curid=39619984 |
Hydrogel encapsulation of quantum dots CdSe QDs have been shown to possess optical properties superior to organic dyes. The ZnS shell has a two-fold effect: Despite their potential for use as contrast agents for medical imaging techniques, their use in vivo is hindered by the cytotoxicity of Cadmium. To address this issue, methods have been developed to “wrap” or “encapsulate” potentially-toxic QDs in bio-inert polymers to facilitate use in living tissue. While Cd-free QDs are commercially available, they are unsuitable for use as a substitute for organic contrasts. Another issue with CdSe(ZnS) nanoparticles is significant hydrophobicity, which hinders their ability to enter solution with aqueous media, such as blood or spinal fluid. Certain hydrophilic polymers could be used to render the dots water-soluble. One notable quantum dot encapsulation technique involves utilizing a double fluoroalkyl-ended polyethylene glycol molecule (R-PEG) as a surfactant, which will spontaneously form micellular structures at its critical micelle concentration (CMC). The critical micelle concentration of the R-PEG depends on the length of the PEG portion of the polymer. This molecule consists of a hydrophilic PEG backbone with two hydrophilic terminal groups (CF-CHCHO) attached via isophorone diurethane. It is synthesized by dehydrating a solution of 1,3-dimethyl-5-fluorouracil and PEG, mixing them in the presence of heavy water (DO) via a sonicator to combine then | https://en.wikipedia.org/wiki?curid=39619984 |
Hydrogel encapsulation of quantum dots At the appropriate Krafft temperature and critical micelle concentration these molecules will form individual tear-drop loops, where the hydrophobic ends are attracted to one another, to other molecules, and also to the similarly hydrophobic QDs. This forms a loaded micelle with a hydrophilic outer shell and a hydrophobic core. When encapsulating hydrophobes in this way it is important to ensure the particle size is appropriate for the PEG backbone being utilized, as the number of PEG mer units (generally with a MW of 6K or 10K Daltons) determines the maximum particle size that can be successfully contained at the core of the micelle. To determine the average diameter, D, of the QDs, the following empirical equation is used: Where It is during encapsulation that the ZnS shell plays an especially important role, in that it helps prevent the agglomeration of CdSe particles that had no shell by occupying the previously-mentioned bonds on the dot’s surface; however, clumping can still occur through secondary forces that arise from common hydrophobicity. This can result in multiple particles within each micelle, which may negatively impact overall resolution. For this reason multiple combinations of PEG chain length and particle diameter are necessary to achieve optimal imaging properties | https://en.wikipedia.org/wiki?curid=39619984 |
Hydrogel encapsulation of quantum dots After initial encapsulation the remaining molecules form connections between the individual micelles to form a network within the aqueous media called a hydrogel, creating a diffuse and relatively constant concentration of the encapsulated particle within the gel. The formation of hydrogels is a phenomenon observed in superabsorbent polymers, or "slush powders," in which the polymer, often in the form of a powder, absorbs water, becoming up to 99% liquid and 30-60 times larger in size. The diffusivity of spherical particles in a suspension is approximated by the Stokes-Einstein equation: Typical R-PEG hydrogel diffusivities for 2 nm quantum dots are on the order of 10 m/s, so suspensions of quantum dots tend to be very stable. Hydrogel viscosity can be determined by using rheological techniques. When encapsulating hydrophobic or potentially toxic materials it is important that the encapsulant remain intact while inside the body. Studying the rheological properties of the micelles permits identification and selection of the polymer that is most appropriate for use in long-term biological applications. R-PEG exhibits superior rheological properties when used "in vivo". The properties of the polymer are influenced by the chain length. The correct chain length ensures that the encapsulant is not released over time. Avoiding the release of QDs and other toxic particles is critical to prevent unintentional cell necrosis in patients | https://en.wikipedia.org/wiki?curid=39619984 |
Hydrogel encapsulation of quantum dots The length of the polymer is controlled by two factors: Increasing the PEG length increases the solubility of the polymer. However, if the PEG chain is too long the micelle will become unstable. It has been observed that a stable hydrogel can only be formed with PEG backbones weighing between six and ten thousand Daltons. On the other hand, increasing the length of the hydrophobic terminal groups decreases aqueous solubility. For a given PEG weight, if the hydrophobe is too short the polymer will just dissolve into the solution, and if it is too long the polymer won’t dissolve at all. Generally, two end groups result in the highest conversion into micelles (91%): At molecular weights between 6 thousand and 10 thousand Daltons the R-PEG hydrogel acts as a Maxwell material, which means the fluid has both viscosity and elasticity. This is determined by measuring the plateau modulus, the elastic modulus for a viscoelastic polymer is constant or "relaxed" when deformed, at a range of frequencies via oscillatory rheology. Plotting the first- vs second-order integrals of the modulus values, a Cole-Cole plot is obtained, which, when fitted to a Maxwell model, provides the following relationship: Where Based on the Maxwellian behavior of the hydrogel and observations of erosion via surface plasmon resonance (SPR), the following data results for 3 common R-PEG types at their specified concentrations: XKCY denotes X thousand Daltons of molecular mass and Y carbon atoms | https://en.wikipedia.org/wiki?curid=39619984 |
Hydrogel encapsulation of quantum dots These values can give us information on the degree of entanglement (or degree of cross linking, depending on what polymer is being considered). In general, higher degrees of entanglement leads to higher time required for the polymer to return to the undeformed state or relaxation times. Hydrogel encapsulation of the QDs opens up a new range of applications, such as: | https://en.wikipedia.org/wiki?curid=39619984 |
Surface chemistry of paper The surface chemistry of paper is responsible for many important paper properties, such as gloss, waterproofing, and printability. Many components are used in the paper-making process that affect the surface. Coating components are subject to particle-particle, particle-solvent, and particle-polymer interactions. Van der Waals forces, electrostatic repulsions, and steric stabilization are the reasons for these interactions. Importantly, the characteristics of adhesion and cohesion between the components form the base coating structure. Calcium carbonate and kaolin are commonly used pigments. Pigments support a structure of fine porosity and form a light scattering surface. The surface charge of the pigment plays an important role in dispersion consistency. The surface charge of calcium carbonate is negative and not dependent on pH, however it can decompose under acidic conditions. Kaolin has negatively charged faces while the charge of its laterals depend on pH, being positive in acidic conditions and negative in basic conditions with an isoelectric point at 7.5. The equation for determining the isoelectric point is as follows: where formula_2 is the interfacial tension between the solid and the liquid, formula_3 is the interfacial tension between the liquid and the vapor, and formula_4 is the interfacial tension between the solid and the vapor. An ideal oleophilic surface would have a contact angle of 0° with oil, therefore allowing the ink to transfer to the paper and be absorbed | https://en.wikipedia.org/wiki?curid=39620647 |
Surface chemistry of paper The hydrocarbon plasma coating provides an oleophilic surface to the paper by lowering the contact angle of the paper with the oil in the ink. The hydrocarbon plasma coating increases the non-polar interactions while decreasing polar interactions which allow paper to absorb ink while preventing dampening water absorption. Printing quality is highly influenced by the various treatments and methods used in creating paper and enhancing the paper surface. Consumers are most concerned with the paper-ink interactions which vary for certain types of paper due to different chemical properties of the surface. Inkjet paper is the most commercially used type of paper. Filter paper is another key type of paper whose surface chemistry affects its various forms and uses. The ability of adhesives to bond to a paper surface is also affected by the surface chemistry. Co-styrene-maleic anhydride and co-styrene acrylate are common binders associated with a cationic starch pigment in Inkjet printing paper. Table 1 shows their surface tension under given conditions. There have been several studies that have focused on how the paper printing quality is dependent on the concentration of these binders and ink pigment. Data from the experiments are congruent and stated in Table 2 as the corrected contact angle of water, the corrected contact angle of black ink, and the total surface energy. The contact angle measurement has proven to be a very useful tool to evaluate the influence of the sizing formulation on the printing properties | https://en.wikipedia.org/wiki?curid=39620647 |
Surface chemistry of paper Surface free energy has also shown to be very valuable in explaining the differences in sample behavior. Various composite coatings were analyzed on filter paper in an experiment done by Wang et al. The ability to separate homogenous liquid solutions based on varying surface tensions has great practical use. Creating superhydrophobic and superoleophilic filter paper was achieved by treating the surface of commercially available filter paper with hydrophobic silica nanoparticles and polystyrene solution in toluene. Oil and water were successfully separated through the use of the filter paper created with an efficiency greater than 96%. In a homogenous solution the filter paper was also successful in separating the liquids through differentiating for surface tensions. Although with a lower efficiency, aqueous ethanol was also extraced from the solution when tested on the filter paper. | https://en.wikipedia.org/wiki?curid=39620647 |
Deep Carbon Observatory The (DCO) is a global research program designed to transform understanding of carbon's role in Earth. DCO is a community of scientists, including biologists, physicists, geoscientists and chemists, whose work crosses several traditional disciplinary lines to develop the new, integrative field of deep carbon science. To complement this research, the DCO's infrastructure includes public engagement and education, online and offline community support, innovative data management, and novel instrumentation development. In December 2018, researchers announced that considerable amounts of life forms, including 70% of bacteria and archea on Earth, comprising up to 23 billion tonnes of carbon, live up to at least deep underground, including below the seabed, according to a ten-year project. In 2007, Robert Hazen, a Senior Staff Scientist at the Carnegie Institution’s Geophysical Laboratory (Washington, DC, USA) spoke at the Century Club in New York, on the origins of life on Earth and how geophysical reactions may have played a critical role in the development of life on Earth. Jesse Ausubel, a faculty member at Rockefeller University and Program Director at the Alfred P. Sloan Foundation, was in attendance and later sought out Hazen's book, "Genesis: The Scientific Quest for Life’s Origins". After two years of planning and collaboration, Hazen and colleagues officially launched the (DCO) in August 2009, with its secretariat based at the Geophysical Laboratory of the Carnegie Institution of Washington, DC | https://en.wikipedia.org/wiki?curid=39621288 |
Deep Carbon Observatory Hazen and Ausubel, along with input from over 100 scientists invited to participate in the Deep Carbon Cycle Workshop in 2008, expanded their original idea. No longer focused solely on the origin of life on Earth, the group instead clarified their position to further human understanding of Earth, carbon, that critical element, had to take center stage. The Deep Carbon Observatory's research considers the global carbon cycle beyond Earth's surface. It explores high-pressure and extreme temperature organic synthesis, complex interactions between organic molecules and minerals, conducts field observations of deep microbial ecosystems and of anomalies in petroleum geochemistry, and constructs theoretical models of lower crust and upper mantle carbon sources and sinks. The is structured around four science communities focused on the topics of reservoirs and fluxes, deep life, deep energy, and extreme physics and chemistry. The Reservoirs and Fluxes Community explores the storage and transport of carbon in Earth's deep interior. The subduction of tectonic plates and volcanic outgassing are primary vehicles for carbon fluxes to and from deep Earth, but the processes and rates of these fluxes, as well as their variation throughout Earth's history, remain poorly understood | https://en.wikipedia.org/wiki?curid=39621288 |
Deep Carbon Observatory In addition DCO research on primitive chondritic meteorites indicates that Earth is relatively depleted in highly volatile elements compared to chondrites, though DCO's research is further examining whether large reservoirs of carbon may be hidden in the mantle and core. Members of the Reservoirs and Fluxes Community are conducting research as a part of the Deep Earth Carbon Degassing Project to make tangible advances towards quantifying the amount of carbon outgassed from the Earth's deep interior (core, mantle, crust) into the surface environment (e.g. biosphere, hydrosphere, cryosphere, atmosphere) through naturally occurring processes. The Deep Life Community documents the extreme limits and global extent of subsurface life in our planet, exploring the evolutionary and functional diversity of Earth's deep biosphere and its interaction with the carbon cycle. The Deep Life Community maps the abundance and diversity of subsurface marine and continental microorganisms in time and space as a function of their genomic and biogeochemical properties, and their interactions with deep carbon. By integrating "in situ" and "in vitro" assessments of biomolecules and cells, the Deep Life Community explores the environmental limits to the survival, metabolism and reproduction of deep life. The resulting data informs experiments and models that study the impact of deep life on the carbon cycle, and the deep biosphere's relation to the surface world | https://en.wikipedia.org/wiki?curid=39621288 |
Deep Carbon Observatory Members of the Deep Life Community are conducting research as a part of the Census of Deep Life, which seeks to identify the diversity and distribution of microbial life in continental and marine deep subsurface environments and to explore mechanisms that govern microbial evolution and dispersal in the deep biosphere. In December 2018, researchers announced that considerable amounts of life forms, including 70% of bacteria and archea on Earth, comprising up to 23 billion tonnes of carbon, live up to at least deep underground, including below the seabed, according to a ten-year project. The Deep Energy Community is dedicated to quantifying the environmental conditions and processes from the molecular to the global scale that control the origins, forms, quantities and movements of reduced carbon compounds derived from deep carbon through deep geologic time. The Deep Energy Community uses field-based investigations of approximately 25 globally representative terrestrial and marine environments to determine processes controlling the origin, form, quantities and movements of abiotic gases and organic species in Earth's crust and uppermost mantle. Deep Energy also uses DCO-sponsored instrumentation, especially revolutionary isotopologue measurements, to discriminate between the abiotic and biotic methane gas and organic species sampled from global terrestrial and marine field sites | https://en.wikipedia.org/wiki?curid=39621288 |
Deep Carbon Observatory Another research activity of Deep Energy is to quantify the mechanisms and rates of fluid-rock interactions that produce abiotic hydrogen and organic compounds as a function of temperature, pressure, fluid and solid compositions. As a result of a series of workshops, the DCO initiated an additional Science Community to examine the physics and chemistry of carbon under extreme conditions. The overarching goal of the Extreme Physics and Chemistry Community is to improve the understanding of the physical and chemical behavior of carbon at extreme conditions, as found in the deep interiors of Earth and other planets. Extreme Physics and chemistry research explores thermodynamics of carbon-bearing systems, chemical kinetics of chemical deep carbon processes, high-pressure biology and biophysics, physical properties of aqueous fluids, theoretical modeling for carbon and its compounds at high pressures and temperatures, and solid-fluid interactions under extreme conditions. The Extreme Physics and Chemistry Community also seeks to identify possible new carbon-bearing materials in Earth and planetary interiors, to characterize the properties of these materials and to identify reactions at conditions relevant to Earth and planetary interiors. As the DCO nears its completion in 2020, it is integrating the discoveries made by its research communities into an overarching model of carbon in Earth, as well as other models and products aimed at both the scientific community and wider public | https://en.wikipedia.org/wiki?curid=39621288 |
Deep Carbon Observatory Research highlights to date include: "Carbon in Earth" is Volume 75 of "Reviews in Mineralogy and Geochemistry" ("RiMG"). It was released as an open access publication on March 11, 2013. Each chapter of "Carbon in Earth" synthesizes what is known about deep carbon, and also outlines unanswered questions that will guide future DCO research. The encourages open access publication, and is striving to become a leader in Earth sciences in this regard. DCO funding can be used to defray the costs of open access publication. Recent advances in data generation techniques lead to increasingly complex data. At the same time, science and engineering disciplines are rapidly becoming more and more data driven with the ultimate aim of better understanding and modeling the dynamics of complex systems. However complex data requires integration of information and knowledge across multiple scales and spanning traditional disciplinary boundaries. Significant advances in methods, tools and applications for data science and informatics over the last five years can now be applied to multi- and inter-disciplinary problem areas. Given these challenges, it is clear that each DCO Research Community faces diverse data science and data management needs to fulfill both their overarching objectives and their day-to-day tasks | https://en.wikipedia.org/wiki?curid=39621288 |
Deep Carbon Observatory The Data Science Team handles the data science and data management needs for each DCO program and for the DCO as a whole, using a combination of informatics methods, use case development, requirements analysis, inventories and interviews. A list of some of the scientists involved in the Deep Carbon Observatory: On 11 April 2020, the Australian Broadcasting Corporation's "Science Show" broadcast a 37 minute radio documentary on the DCO. | https://en.wikipedia.org/wiki?curid=39621288 |
C26H38O2 The molecular formula CHO may refer to: | https://en.wikipedia.org/wiki?curid=39630333 |
C23H34O3 The molecular formula CHO may refer to: | https://en.wikipedia.org/wiki?curid=39630350 |
C25H38O3 The molecular formula CHO may refer to: | https://en.wikipedia.org/wiki?curid=39630505 |
Indirect immunoperoxidase assay (IPA) is a laboratory technique used to detect and titrate viruses that do not cause measurable cytopathic effects and cannot be measured by classical plaque assays. These viruses include human coronavirus 229E and OC43. Susceptible cells are inoculated with serial logarithmic dilutions of samples in a 96-well plate. After viral growth, viral detection by IPA yields the infectious virus titer, expressed as tissue culture infectious dose (TCID50). This represents the dilution of a virus-containing sample at which half of a series of laboratory wells contain replicating viruses. This technique is a reliable method for the titration of human coronaviruses (HCoV) in biological samples (cells, tissues, or fluids). It is also reliable in the detection of antibodies to human cytomegalovirus. | https://en.wikipedia.org/wiki?curid=39630507 |
C25H36O2 The molecular formula CHO may refer to: | https://en.wikipedia.org/wiki?curid=39630660 |
Self-assembly of nanoparticles The empirical definition of self-assembly is typically given as a phenomenon where the components of a system assemble themselves to form a larger functional unit. This spontaneous organization can be due to direct specific interaction, collective effects, and/or occur indirectly through their environment. This definition mirrors the one provided by Nature.com and is applicable to a variety of components regardless of their dimensions. The thermodynamics-based definition of self-assembly was introduced by Nicholas A. Kotov and describes self-assembly as a process where components of the system acquire non-random spatial distribution with respect to each other and the boundaries of the system. This definition allows one to account for mass and energy fluxes taking place in the self-assembly processes and is specifically applicable to the processes of spontaneous organization of nanoparticles with each other and with the boundaries of the system. Due to the proliferation of nanoparticle synthesis techniques, the study and design of nanoparticle self-assembly has become widespread. The spatial arrangements of these self-assembled nanoparticles can be potentially used to build increasingly complex structures leading to a wide variety of materials that can be used for different purposes. At the molecular level, intermolecular force hold the spontaneous gathering of molecules into a well-defined and stable structure together | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles In chemical solutions, self-assembly is an outcome of random motion of molecules and the affinity of their binding sites for one another. In the area of nanotechnology, developing a simple, efficient method to organize molecules and molecular clusters into precise, pre-determined structure is crucial. In 1959, physicist Richard Feynman gave a talk titled “"There’s Plenty of Room at the Bottom"] to the American Physical Society. He imagined a world in which “we could arrange atoms one by one, just as we want them.” This idea set the stage for the bottom-up synthesis approach in which constituent components interact to form higher-ordered structures in a controllable manner. The study of self-assembly of nanoparticles began with recognition that some properties of atoms and molecules enable them to arrange themselves into patterns. A variety of applications where the self-assembly of nanoparticles might be useful. For example, building sensors or computer chips. Nanoparticles have been observed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction] to self-assemble in real-time. Definition Self-assembly is defined as a process in which individual units of material associate with themselves spontaneously into a defined and organized structure or larger units with minimal external direction. Self-assembly is recognized as a highly useful technique to achieve outstanding qualities in both organic and inorganic nanostructures | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles Importance Self assembly of nanomaterials is currently considered broadly for nano-structuring and nano-fabrication because of its simplicity, versatility and spontaneity. Exploiting the properties of the nano assembly holds promise as a low-cost and high-yield technique for a wide range of scientific and technological applications and is a key research effort in nanotechnology, molecular robotics, and molecular computation. A summary of benefits of self-assembly in fabrication is listed below: Challenges There exist several outstanding challenges in self-assembly, as it is a relatively new field in nanotechnology. Currently self-assembly is difficult to control on large scales, and to be widely applied we will need to ensure high degrees of reproducibility at these scales. The fundamental thermodynamic and kinetic mechanisms of self-assembly are poorly understood - the basic principles of atomistic and macroscale processes can be significantly different than those for nanostructures. Concepts related to thermal motion and capillary action influence equilibrium timescales and kinetic rates that are not well defined in self-assembling systems. Top-down vs bottom-up synthesis A bottom up approach for nano-assembly is a primary research target for nano-fabrication because top down synthesis is expensive (requiring external work) and is not selective on very small lengthscales, but is currently the primary mode of industrial fabrication | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles Generally,the maximum resolution of the top-down products is much coarser than those of bottom-up; therefore, an accessible strategy to bridge “bottom-up” and “top-down,” is realizable by the principles of self-assembly [23]. By controlling local intermolecular forces to find the lowest-energy configuration, self-assembly can be guided by templates to generate similar structures to those currently fabricated by top-down approaches. This so-called bridging will enable fabrication of materials with the fine resolution of bottom-up methods and the larger range and arbitrary structure of top-down processes.[15] Furthermore, in some cases components are too small for top-down synthesis, so self-assembly principles are required to realize these novel structures. Classification Nanostructures can be organized into groups based on their size, function, and structure; this organization is useful to define the potential of the field. By size: Among the more sophisticated and structurally complex nanostructures currently available are organic macromolecules, wherein their assembly relies on the placement of atoms into molecular or extended structures with atomic-level precision. It is now known that organic compounds can be conductors, semiconductors, and insulators, thus one of the main opportunities in nanomaterials science is to use organic synthesis and molecular design to make electronically useful structures | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles Structural motifs in these systems include colloids, small crystals, and aggregates on the order of 1-100 nm. By function: Nanostructured materials can also be classed according to their functions, for example nanoelectronics and information technology (IT). Lateral dimensions used in information storage are shrinking from the micro- to the nanoscale as fabrication technologies improve. Optical materials are important in the development of miniaturized information storage because light has many advantages for storage and transmission over electronic methods. Quantum dots - most commonly CdSe nanoparticles having diameters of tens of nm, and with protective surface coatings - are notable for their ability to fluoresce over a broad range of the visible spectrum, with the controlling parameter being size. By structure: Certain structural classes are especially relevant to nanoscience. As the dimensions of structures become smaller, their surface area-to-volume ratio increases. Much like molecules, nanostructures at small enough scales are essentially "all surface". The mechanical properties of materials are strongly influenced by these surface structures. Fracture strength and character, ductility, and various mechanical moduli all depend on the substructure of the materials over a range of scales. The opportunity to redevelop a science of materials that are nanostructured by design is largely open. Self-assembly is an equilibrium process, i.e. the individual and assembled components exist in equilibrium | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles In addition, the flexibility and the lower free energy conformation is usually a result of a weaker intermolecular force between self-assembled moieties and is essentially enthalpic in nature. The thermodynamics of the self-assembly process can be represented by a simple Gibbs free energy equation: where if formula_2 is negative, self-assembly is a spontaneous process. formula_3 is the enthalpy change of the process and is largely determined by the potential energy/intermolecular forces between the assembling entities. formula_4 is the change in entropy associated with the formation of the ordered arrangement. In general, the organization is accompanied by a decrease in entropy and in order for the assembly to be spontaneous the enthalpy term must be negative and in excess of the entropy term. This equation shows that as the value of formula_5 approaches the value of formula_3 and above a critical temperature, the self-assembly process will become progressively less likely to occur and spontaneous self-assembly will not happen. The self-assembly is governed by the normal processes of nucleation and growth. Small assemblies are formed because of their increased lifetime as the attractive interactions between the components lower the Gibbs free energy. As the assembly grows, the Gibbs free energy continues to decrease until the assembly becomes stable enough to last for a long period of time | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles The necessity of the self-assembly to be an equilibrium process is defined by the organization of the structure which requires non-ideal arrangements to be formed before the lowest energy configuration is found. Kinetics The ultimate driving force in self-assembly is energy minimization and the corresponding evolution towards equilibrium, but kinetic effects can also play a very strong role. These kinetic effects, such as trapping in metastable states, slow coarsening kinetics, and pathway-dependent assembly, are often viewed as complications to be overcome in, for example, the formation of block copolymers. Amphiphile self-assembly is an essential bottom-up approach of fabricating advanced functional materials. Self-assembled materials with desired structures are often obtained through thermodynamic control. Here, we demonstrate that the selection of kinetic pathways can lead to drastically different self-assembled structures, underlining the significance of kinetic control in self-assembly. Self-assembled structure contain defects. Dislocations caused during the assembling of nanomaterials can majorly affect the final structure and in general defects are never completely avoidable. Current research on defects is focused on controlling defect density.[23] In most cases, the thermodynamic driving force for self-assembly is provided by weak intermolecular interactions and is usually of the same order of magnitude as the entropy term | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles In order for a self-assembling system to reach the minimum free energy configuration, there has to be enough thermal energy to allow the mass transport of the self-assembling molecules. For defect formation, the free energy of single defect formation is given by: The enthalpy term, formula_8 does not necessarily reflect the intermolecular forces between the molecules, it is the energy cost associated with disrupting the pattern and may be thought of as a region where optimum arrangement does not occur and the reduction of enthalpy associated with ideal self-assembly did not occur. An example of this can be seen in a system of hexagonally packed cylinders where defect regions of lamellar structure exist. If formula_9 is negative, there will be a finite number of defects in the system and the concentration will be given by: N is the number of defects in a matrix of N self-assembled particles or features and formula_11 is the activation energy of defect formation. The activation energy, formula_12, should not be confused with formula_8. The activation energy represents the energy difference between the initial ideally arranges state and a transition state towards the defective structure. At low defect concentrations, defect formation is entropy driven until a critical concentration of defects allows the activation energy term to compensate for entropy. There is usually an equilibrium defect density indicated at the minimum free energy | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles The activation energy for defect formation increases this equilibrium defect density. Intermolecular forces govern the particle interaction in self-assembled systems. The forces tend to be intermolecular in type rather than ionic or covalent because ionic or covalent bonds will “lock” the assembly into non-equilibrium structures. The types intermolecular forces seen in self-assembly processes are van der Waals, hydrogen bonds, and weak polar forces, just to name a few. In self-assembly, regular structural arrangements are frequently observed, therefore there must be a balance of attractive and repulsive between molecules otherwise an equilibrium distance will not exist between the particles. The repulsive forces can be electron cloud-electron cloud overlap or electrostatic repulsion. The processes by which nanoparticles self-assemble are widespread and important. Understanding why and how self-assembly occurs is key in reproducing and optimizing results. Typically, nanoparticles will self-assemble for one or both of two reasons: molecular interactions and external direction. Nanoparticles have the ability to assemble chemically through covalent or noncovalent interactions with their capping ligand. The terminal functional group(s) on the particle are known as capping ligands. As these ligands tend to be complex and sophisticated, self-assembly can provide a simpler pathway for nanoparticle organization by synthesizing efficient functional groups | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles For instance, DNA oligomers have been a key ligand for nanoparticle building blocks to be self-assembling via sequence-based specific organization. However, to deliver precise and scalable (programmable) assembly for a desired structure, a careful positioning of ligand molecules onto the nanoparticle counterpart should be required at the building block (precursor) level, such as direction, geometry, morphology, affinity, etc. The successful design of ligand-building block units can play an essential role in manufacturing a wide-range of new nano systems, such as nanosensor systems, nanomachines/nanobots, nanocomputers, and many more uncharted systems. Nanoparticles can self-assemble as a result of their intermolecular forces. As systems look to minimize their free energy, self-assembly is one option for the system to achieve its lowest free energy thermodynamically. Nanoparticles can be programmed to self-assemble by changing the functionality of their side groups, taking advantage of weak and specific intermolecular forces to spontaneously order the particles. These direct interparticle interactions can be typical intermolecular forces such as hydrogen bonding or Van der Waals forces, but can also be internal characteristics, such as hydrophobicity or hydrophilicity. For example, lipophilic nanoparticles have the tendency to self-assemble and form crystals as solvents are evaporated | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles While these aggregations are based on intermolecular forces, external factors such as temperature and pH also play a role in spontaneous self-assembly. As nanoparticle interactions take place on a nanoscale, the particle interactions must be scaled similarly. Hamaker interactions take into account the polarization characteristics of a large number of nearby particles and the effects they have on each other. Hamaker interactions sum all of the forces between all particles and the solvent(s) involved in the system. While Hamaker theory generally describes a macroscopic system, the vast number of nanoparticles in a self-assembling system allows the term to be applicable. Hamaker constants for nanoparticles are calculated using Lifshitz theory, and can often be found in literature. The natural ability of nanoparticles to self-assemble can be replicated in systems that do not intrinsically self-assemble. Directed self-assembly (DSA) attempts to mimic the chemical properties of self-assembling systems, while simultaneously controlling the thermodynamic system to maximize self-assembly. External fields are the most common directors of self-assembly. Electric and magnetic fields allow induced interactions to align the particles. The fields take advantage of the polarizability of the nanoparticle and its functional groups. When these field-induced interactions overcome random Brownian motion, particles join to form chains and then assemble | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles At more modest field strengths, ordered crystal structures are established due to the induced dipole interactions. Electric and magnetic field direction requires a constant balance between thermal energy and interaction energies. Common ways of incorporating nanoparticle self-assembly with a flow include Langmuir-Blodgett, dip coating, flow coating and spin coating. Macroscopic viscous flow fields can direct self-assembly of a random solution of particles into ordered crystals. However, the assembled particles tend to disassemble when the flow is stopped or removed. Shear flows are useful for jammed suspensions or random close packing. As these systems begin in nonequilibrium, flow fields are useful in that they help the system relax towards ordered equilibrium. Flow fields are also useful when dealing with complex matrices that themselves have rheological behavior. Flow can induce anisotropic viseoelastic stresses, which helps to overcome the matrix and cause self-assembly. Large amplitude oscillatory shear (LAOS) is most effective for particles that are 100 nm-1 µm in size. Hard and soft shears can order in steady shear. However, this assembly strongly relies on particle volume fraction, particle interaction potentials, polydisterity, and shear rate and strain. The large amount of directing factors can cause complications in directing self-assembly by LAOS. Diblock copolymer micells have been studied in regard to structuring nanoparticles in bulk | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles The most effective self-assembly director is a combination of fields. If the fields and conditions are optimized, self-assembly can be permanent and complete. When a field combination is used with nanoparticles that are tailored to be intrinsically responsive, the most complete assembly is observed. Combinations of fields allow the benefits of self-assembly, such as scalability and simplicity, to be maintained while being able to control orientation and structure formation. Field combinations possess the greatest potential for future directed self-assembly work. Nano-particles can self-assemble on solid surfaces after applying external forces (like magnetic, electric, and flow) as mentioned in the above section. Templates made of microstructures like carbon nanotubes or block polymers can also be used to assist in self-assembly; they cause directed self-assembly (DSA) in which active sites are embedded to selectively induce nanoparticle deposition. Such templates are considered as any object onto which different particles can be arranged into a structure with a morphology similar to that of the template. Carbon nanotubes (microstructures), single molecules, or block copolymers are common templates. Nanoparticles are often shown to self-assemble within distances of nanometers and micrometers, but block copolymer templates can be used to form well-defined self-assemblies over macroscopic distances | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles By incorporating active sites to the surfaces of nanotubes and polymers, the functionalization of these templates can be transformed to favor self-assembly of specified nanoparticles. Pickering and Ramsden explained the idea of pickering emulsions when experimenting with paraffin-water emulsions with solid particles like iron oxide and silicon dioxide. They observed that the micron-sized colloids generated a resistant film at the interface between the two immiscible phases, inhibiting the coalescence of the emulsion drops. These Pickering emulsions, as shown in the figure below, are formed from the self-assembly of colloidal particles in two-part liquid systems, such as oil-water systems. The desorption energy, which is directly related to the stability of emulsions depends on the particle size, particle-particle interaction and, of course, particle-water and particle-oil interactions. A decrease in total free energy was observed to be a result from the assembly of nanoparticles at an oil/water (O/W) interface. This is shown in the following equation in which a particle with radius r at an interface between oil (O) and water (W) results in a decrease of the initial interfacial energy E to E; this difference in energy is ΔE. At a fixed γ, γ, and γ, the equation shows that the stability of a particle assembly is determined by the radius square. When moving to the interface, particles reduce the unfavorable contact between the immiscible fluids and decrease the interfacial energy | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles The decrease in total free energy for microscopic particles is much larger than that of thermal energy; this results in an effective confinement of large colloids to the interface. They are irreversibly bound to the interface. Nanoscopic particles are restricted to the interface by an energy reduction comparable to thermal energy. Thus, nanoparticles are easily displaced from the interface. A constant particle exchange then occurs at the interface; the rate of this exchange depends on particle size. The thermally activated escape of small particles occurs more often than larger particles. For the equilibrium state of assembly, the total gain in free energy is smaller for smaller particles. Thus, large nanoparticles assemblies are more stable. This size dependence allows nanoparticles to self-assemble at the interface to attain its equilibrium structure. Micrometer- size colloids, on the other hand, may be confined in a non-equilibrium state. The interfacial tension and the wettability of a particle surface affect the desorption energy. The contact angle θ between the solid and the oil/water interface determines its wettability. As shown in the figure below, a contact angle θ greater than 90° favors a water-in-oil emersion while a contact angle θ less than 90° favors oil-in-water emulsion. These contact angles affect the stability of the emulsion. A maximum desorption energy peak is observed at a contact angle of 90° | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles When the contact angle is greater than or less than this point, the desorption energy gradually decreases; thus, the stability of the emulsion decreases as well. Material that consists with nano-particles is called "nanostructured material". The phase of "nanostructured material" implies two important ideas: Self-assembly of nanoscale structures from functional nanoparticles has provided a powerful path to developing small and powerful electronic components. The difficulty of applied nanostructure material is nanoscale objects have always been difficult to manipulate because they cannot be characterized by molecular techniques and they are too small to observe optically. 2D self-assembly monodisperse particle colloids has a strong potential in dense magnetic storage media. Each colloid particle has the ability to store information as known as binary number 0 and 1 after applying it to a strong magnetic field. In the meantime, it requires a nanoscale sensor or detector in order to selectively choose the colloid particle. Block copolymers are a well-studied and versatile class of self-assembling materials characterized by chemically distinct polymer blocks that are covalently bonded. This molecular architecture of the covalent bond enhancement is what causes block copolymers to spontaneously form nanoscale patterns. These copolymers are a well-studied and versatile class of self-assembling materials characterized by chemically distinct polymer blocks that are covalently bonded | https://en.wikipedia.org/wiki?curid=39631094 |
Self-assembly of nanoparticles This molecular architecture of the covalent bond enhancement, is what causes block copolymers to spontaneously form nanoscale patterns. These copolymers offer the ability to self-assemble into uniform, nanosized micelles and accumulate in tumors via the enhanced permeability and retention effect. Polymer composition can be chosen to control the micelle size and compatibility with the drug of choice. The challenges of this application are the difficulty of reproducing or controlling the size of self-assembly nano micelle, preparing predictable size-distribution, and the stability of the micelle with high drug load content. Magnetic nanochains are a class of new magnetoresponsive and superparamagnetic nanostructures with highly anisotropic shapes (chain-like) which can be manipulated using magnetic field and magnetic field gradient. The magnetic nanochains possess attractive properties which are significant added value for many potential uses including magneto-mechanical actuation-associated nanomedicines in low and super-low frequency alternating magnetic field and magnetic drug delivery. | https://en.wikipedia.org/wiki?curid=39631094 |
Excimer lamp An excimer lamp (or excilamp) is a source of ultraviolet light produced by spontaneous emission of excimer (exciplex) molecules. Excimer lamps are quasimonochromatic light sources operating over a wide range of wavelengths in the ultraviolet (UV) and vacuum ultraviolet (VUV) spectral regions. Operation of an excimer lamp is based on the formation of exci"ted" dimers (excimers), which spontaneously transiting from the excited state to the ground state result in the emission of UV-photons. The spectral maximum of excimer lamp radiation is specified by a working excimer molecule (see table below).<br> <br> Wavelength and photon energy of excimer lamp radiation. Excimers are diatomic molecules (dimers) or polyatomic molecules that have stable excited electronic states and an unbound or weakly bound (thermally unstable) ground state. Initially, only homonuclear diatomic molecules with a stable excited state but a repulsive ground state were called excimers (exci"ted" dimers). The term "excimer" was later extended to refer any polyatomic molecule with a repulsive or weakly bound ground state. One can also come across the term "exciplex", meaning an exci"ted" complex. It is also an excimer molecule but not a homonuclear dimer. For instance, Xe*, Kr*, Ar* are excimer molecules, while XeCl*, KrCl*, XeBr*, ArCl*, XeCl* are referred to exciplex molecules. Dimers of rare gases and rare gas-halogen dimers are the most spread and studied excimers | https://en.wikipedia.org/wiki?curid=39632612 |
Excimer lamp Rare gas-halide trimers, metal excimers, metal-rare gas excimers, metal-halide excimers, and rare gas-oxide excimers are also known, but they are rarely used. An excimer molecule can exist in an excited electronic state for a limited time, as a rule from a few to a few tens of nanoseconds. After that, an excimer molecule transits to the ground electronic state, while releasing the energy of internal electronic excitation in the form of a photon. Owing to a specific electronic structure of an excimer molecule, the energy gap between the lowest bound excited electronic state and the ground state amounts from 3.5 to 10 eV, depending on a kind of an excimer molecule and provides light emission in the UV and VUV spectral region. A typical spectral characteristic of excimer lamp radiation consists mainly of one intense narrow emission band. About 70-80% of the whole radiation power of an excimer lamp is concentrated in this emission band. The full-width at half maximum of the emission band depends on a kind of an excimer molecule and excitation conditions and ranges within 2 to 15 nm. In fact, excimer lamps are sources of quasimonochromatic light. Therefore, such sources are suitable for spectral-selective irradiation and can even replace lasers in some cases. Radiation is produced owing to the spontaneous transition of an excimer molecule from an excited electronic state to the ground state. Excimer and exciplex molecules are not long-living formations | https://en.wikipedia.org/wiki?curid=39632612 |
Excimer lamp They rapidly decompose typically within a few nanoseconds, releasing their excitation energy in the form of a UV photon: emission of an excimer molecule: emission of an exciplex molecule: where "Rg*" is an excimer molecule, "RgX*" is an exciplex molecule, "Rg" is an atom of rare gas, and "X" is an atom of halogen. It is convenient to generate excimer molecules in a plasma. Electrons play an important role in a plasma and, in particular, in the formation of excimer molecules. To be able generating efficiently excimer molecules, the working medium (plasma) should contain sufficient concentration of electrons with energies that are high enough to produce the precursors of the excimer molecules, which are mainly excited and ionized rare gas atoms. Introduction of power into a gaseous mixture results in the formation of excited and ionized rare gas atoms as follows: electron excitation direct electron ionization stepwise ionization where "Rg*" is a rare gas atom in an excited electronic state, "Rg" is a rare gas ion, and "e" is an electron. When there are enough excited rare gas atoms accumulated in a plasma, the excimer molecules are formed by the following reaction: where "Rg*" is an excimer molecule, and "M" is a third particle carrying away the excess energy to stabilize an excimer molecule. As a rule, it is a rare gas atom of the working medium | https://en.wikipedia.org/wiki?curid=39632612 |
Excimer lamp Analyzing this three-body reaction, one can see that the efficiency of the production of excimer molecules is proportional to the concentration of excited rare gas atoms and the square of the concentration of rare gas atoms in the ground state. From this point of view, the concentration of rare gas in the working medium should be as high as possible. A higher concentration of rare gas is achieved by increasing gas pressure. However, an increase in the concentration of rare gas also intensifies the collisional quenching of excimer molecules, resulting in their radiationless decay: The collisional quenching of excimer molecules is negligible while the mean time between collisions is much higher than the lifetime of an excimer molecule in an excited electronic state. In practice, the optimal pressure of a working medium is found experimentally, and it amounts approximately to one atmosphere. A mechanism underlying the formation of exciplex molecules (rare gas halides) is a bit more complicated than the mechanism of excimer molecule formation. The formation of exciplex molecules occurs in two main ways. The first way is due to a reaction of ion-ion recombination, i.e., recombination of a positive rare gas ion and a negative halogen ion: where "RgX*" is an exciplex molecule, and "M" is a collisional third partner, which is usually an atom or molecule of a gaseous mixture or buffer gas. The third particle takes the excess energy and stabilizes an exciplex molecule | https://en.wikipedia.org/wiki?curid=39632612 |
Excimer lamp The formation of a negative halogen ion results from the interaction of a low-energy electron with a halogen molecule in a so-called process of the dissociative electron attachment: where "X" is a halogen atom. The pressure of a gaseous mixture is of great importance for efficient production of exciplex molecules due to the reaction of ion-ion recombination. The fact is that the reaction of ion-ion recombination is a process of a three-body collision, and the probability of a triple collision increases with pressure. At low pressures of a gaseous mixture (several tens of torrs), the reaction of ion-ion recombination is of little efficiency, while it is quite productive at pressures above 100 Torr. The second way of the formation of exciplex molecules is a harpoon reaction. In this case, a halogen molecule or halogen-containing compound captures a weakly bound electron of an excited rare gas atom, and an exciplex molecule in an excited electronic state is formed: Since the harpoon reaction is a process of a two-body collision, it can proceed productively at a pressure significantly lower than that required for a three-body reaction. Thus, the harpoon reaction makes possible the efficient operation of an excimer lamp at low pressures of a gaseous mixture. The collisional quenching of exciplex molecules at low pressures of a gaseous mixture is much lower than at pressures required for productive proceeding the reaction of ion-ion recombination | https://en.wikipedia.org/wiki?curid=39632612 |
Excimer lamp Due to this, a low-pressure excimer lamp ensures the maximum efficiency in converting the pumping energy to UV radiation. It should be mentioned that both the harpoon reaction and reaction of ion-ion recombination proceed simultaneously. The dominance of the first or second reaction is mainly determined by the pressure of a gaseous mixture. The harpoon reaction predominates at low pressures (below 50 Torr), while the reaction of ion-ion recombination prevails at higher pressures (above 100 Torr). The kinetics of reactions proceeding in a plasma is diverse and is not limited to the processes considered above. The efficiency of producing exciplex molecules depends on the composition of a gaseous mixture and conditions of its excitation. Type of a halogen donor plays an important role. The most effective and widely used halogen-carriers are homonuclear diatomic halogen molecules. More complex halogen compounds such as hydrogen halides, metal halides, and interhalogens are also used as a halogen-carrier but to a lesser extent. A noteworthy halogen-carrier is alkali halide. A feature of alkali halides is a similarity of their chemical bond with that of exciplex molecules in excited electronic states. Exciplex molecules in excited electronic states are characterized by the ionic bond as well as alkali halides in the ground state | https://en.wikipedia.org/wiki?curid=39632612 |
Excimer lamp It opens up alternative mechanisms for the formation of exciplex molecules, namely substitution reactions: where "AX" is an alkali halide molecule, "A" is an alkali metal atom, and "A" is an alkali metal ion. These mechanisms of the formation of exciplex molecules are fundamentally different from the reaction of ion-ion recombination and harpoon reaction. An exciplex molecule is formed simply by replacing an atom/ion of alkali metal from an alkali halide molecule by an excited atom/ion of rare gas. An advantage of using alkali halides is that both the substitution reactions can simultaneously proceed at low pressures with comparable productivity. Moreover, both excited atoms and ions of rare gas are effectively used in the production of exciplex molecules in contrast to excimer lamps using other halogen-carriers. It is of importance because the ionization and excitation of rare gas consume most of the introduced energy. Since the reaction of ion-ion recombination and harpoon reaction dominate depending on the pressure of a gaseous mixture, the generation of rare gas ions is unprofitable at low pressures, while the excitation of rare gas is unreasonable at high pressures. A drawback of using alkali halides is high temperatures required for providing the necessary concentration of alkali halide molecules in a gaseous mixture. Despite this, the use of alkali halides as a halogen-carrier is especially promising in the development of exciplex lasers operating at low pressures | https://en.wikipedia.org/wiki?curid=39632612 |
Excimer lamp One of the widely used ways to excite emission of excimer molecules is an electric discharge. There are a lot of discharge types used for pumping excimer lamps (some of them are a glow discharge, pulsed discharge, capacitive discharge, longitudinal and transverse discharges, volume discharge, spark discharge, microhollow discharge, etc.). Currently, excimer lamps with capacitive discharge type of excitation, namely dielectric barrier discharge, are the most widely spread. Excimer lamps using this type of discharge are the most common commercially available. A benefit of the DBD excimer lamps is that the electrodes are not in direct contact with the active medium (plasma). Absence of interaction between the electrodes and the discharge eliminates electrode corrosion as well as contamination of the active medium by sputtered electrode material that considerably increases the lifetime of the DBD excimer lamps in comparison with others. Moreover, a dielectric barrier discharge ensures effective excitation of a gas mixture in a wide range of working pressures from a few torrs to the atmosphere and higher. Excimer lamps can be made in any desired shape of the radiating surface, satisfying requirements of a specific task. The main advantages of excimer lamps over other sources of UV and VUV radiation are as follows: Light sources emitting in the UV spectral region are widely used in techniques involving photo-chemical processes, e.g | https://en.wikipedia.org/wiki?curid=39632612 |
Excimer lamp , drying up adhesive or printing-inks, photolithography, UV induced growth of dielectrics, UV induced surface modification, and cleaning or material deposition. Incoherent sources of UV radiation have some advantages over laser sources because of their lower cost, a huge area of irradiation, and ease of use, especially when large-scale industrial processes are envisaged. Mercury lamps (λ = 253.7 nm) are widely spread UV sources, but their production, use, and disposal of old lamps pose a threat to human health and environmental pollution. Comparing with commonly used mercury lamps, excimer lamps have a number of advantages. A specific feature of an excimer molecule is the absence of a strong bond in the ground electronic state. Thanks to this, high-intensity UV radiation can be extracted from a plasma without significant self-absorption. This makes possible to convert efficiently energy deposited to the active medium into UV radiation. Excimer lamps are referred to cold sources of UV radiation since the radiating surface of excimer lamps remains at relatively low temperatures in contrast with traditional UV lamps like a mercury one. Owing to the absence of necessity for heating, excimer lamps attain the operating conditions practically at once after turning on the power. Rare gas and rare gas-halide excimer lamps generally radiate in the ultraviolet (UV) and vacuum-ultraviolet (VUV) spectral regions (see table) | https://en.wikipedia.org/wiki?curid=39632612 |
Excimer lamp Their unique narrow-band emission characteristics, high quantum efficiency, and high-energy photons make them suitable for applications such as absorption spectroscopy, UV curing, UV coating, sterilization, ozone generation, destruction of gaseous organic waste, photo-etching and photo-deposition and more other applications. Light sources emitting photons in the energy range of 3.5-10 eV find applications in many fields due to the ability of high-energy photons to cleave most chemical bonds and kill microbes destroying nucleic acids and disrupting their DNA. Examples of excimer lamp applications include purification and disinfection of drinking water, pool water, air, sewage purification, decontamination of industrial waste, photochemical synthesis and degradation of organic compounds in flue gases and water, photopolymerization of organic coatings and paints, and photo-enhanced chemical vapor deposition. In all cases UV photons excite species or cleave chemical bonds, resulting in the formation of radicals or other chemical reagents, which initiate a required reaction. An excimer lamp has selective action. UV radiation of a given wavelength can selectively excite species or generate required radicals. Such lamps can be useful for photophysical and photochemical processing such as UV curing of paints, varnishes, and adhesives, cleansing and modifying surface properties, polymerization of lacquers and paints, and photo-degradation of a variety of pollutants | https://en.wikipedia.org/wiki?curid=39632612 |
Excimer lamp Photo-etching of polymers is possible using different wavelengths: 172 nm by xenon excimer, 222 nm by krypton chloride, and 308 nm by xenon chloride. Excimer UV sources can be used for microstructuring large-area polymer surfaces. XeCl-excimer lamps (308 nm) are especially suitable to get tan. Fluorescence spectroscopy is one of the most common methods for detecting biomolecules. Biomolecules can be labeled with fluoroprobe, which then is excited by a short pulse of UV light, leading to re-emission in the visible spectral region. Detecting this re-emitted light, one can judge the density of labeled molecules. Lanthanide complexes are commonly used as fluoroprobes. Due to their long lifetime, they play an important role in Forster resonance energy transfer (FRET) analysis. At present, excimer lamps are coming into use in ecology, photochemistry, photobiology, medicine, criminalistics, petrochemistry, physics, microelectronics, different engineering tasks, wide-ranging technologies, science, various branches of industry including the food industry, and many others. Mercury lamps are the most common source of UV radiation due to their high efficiency. However, the use of mercury in these lamps poses disposal and environmental problems. On the contrary, excimer lamps based on rare gases are absolutely non-hazardous and excimer lamps containing halogen are more environmentally benign than mercury ones. | https://en.wikipedia.org/wiki?curid=39632612 |
Surface chemistry of neural implants As with any material implanted in the body, it is important to minimize or eliminate foreign body response and maximize effectual integration. Neural implants have the potential to increase the quality of life for patients with such disabilities as Alzheimer's, Parkinson's, epilepsy, depression, and migraines. With the complexity of interfaces between a neural implant and brain tissue, adverse reactions such as fibrous tissue encapsulation that hinder the functionality, occur. Surface modifications to these implants can help improve the tissue-implant interface, increasing the lifetime and effectiveness of the implant. Intracranial electrodes consist of conductive electrode arrays implanted on a polymer or silicon, or a wire electrode with an exposed tip and insulation everywhere that stimulation or recording is not desired. Biocompatibility is essential for the entire implant, but special attention is paid to the actual electrodes since they are the site producing the desired function. One main physiological issue that current long-term implanted electrodes suffer from are fibrous glial encapsulations after implantation. This encapsulation is due to the poor biocompatibility and biostability (integration at the hard electrode and soft tissue interface) of many neural electrodes being used today. The encapsulation causes a reduced signal intensity because of the increased electrical impedance and decreased charge transfer between the electrode and the tissue | https://en.wikipedia.org/wiki?curid=39636406 |
Surface chemistry of neural implants The encapsulation causes decreased efficiency, performance, and durability. Electrical impedance is the opposition to current flow with an applied voltage, usually represented as "Z" in units of ohms (Ω). The impedance of an electrode is especially important as it is directly related to its effectiveness. A high impedance causes poor charge transfer and thus poor electrode performance for either stimulating or recording the neural tissue. Electrode impedance is related to surface area at the interface between the electrode and the tissue. At electrode sites, the total impedance is controlled by the double-layer capacitance. The capacitance value is directly related to the surface area. Increasing the surface area at the electrode-tissue interface will increase the capacitance and thus decrease the impedance. The equation below describes the inverse relationship between the capacitance and impedance. Proteins are typically added to the material surface via self-assembled monolayer (SAM) formation. | https://en.wikipedia.org/wiki?curid=39636406 |
Self-healing hydrogels are a specialized type of polymer hydrogel. A hydrogel is a macromolecular polymer gel constructed of a network of crosslinked polymer chains. Hydrogels are synthesized from hydrophilic monomers by either chain or step growth, along with a functional crosslinker to promote network formation. A net-like structure along with void imperfections enhance the hydrogel's ability to absorb large amounts of water via hydrogen bonding. As a result, hydrogels, self-healing alike, develop characteristic firm yet elastic mechanical properties. Self-healing refers to the spontaneous formation of new bonds when old bonds are broken within a material. The structure of the hydrogel along with electrostatic attraction forces drive new bond formation through reconstructive covalent dangling side chain or non-covalent hydrogen bonding. These flesh-like properties have motivated the research and development of self-healing hydrogels in fields such as reconstructive tissue engineering as scaffolding, as well as use in passive and preventive applications. A variety of different polymerization methods may be utilized for the synthesis of the polymer chains that make up hydrogels. Their properties depend to an important extent on how these chains are crosslinked. Crosslinking is the process of joining two or more polymer chains. Both chemical and physical crosslinking exists | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels In addition, both natural polymers such as proteins or synthetic polymers with a high affinity for water may be used as starting materials when selecting a hydrogel. Different crosslinking methods can be implemented for the design of a hydrogel. By definition, a crosslinked polymer gel is a macromolecule that solvent will not dissolve. Due to the polymeric domains created by crosslinking in the gel microstructure, hydrogels are not homogenous within the selected solvent system. The following sections summarize the chemical and physical methods by which hydrogels are crosslinked. Hydrogen bonding is a strong intermolecular force that forms a special type of dipole-dipole attraction. Hydrogen bonds form when a hydrogen atom bonded to a strongly electronegative atom is around another electronegative atom with a lone pair of electrons. Hydrogen bonds are stronger than normal dipole-dipole interactions and dispersion forces but they remain weaker than covalent and ionic bonds. In hydrogels, structure and stability of water molecules are highly affected by the bonds. The polar groups in the polymer strongly bind water molecules and form hydrogen bonds which also cause hydrophobic effects to occur. These hydrophobic effects can be exploited to design chemically crosslinked hydrogels that exhibit self healing abilities | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels The hydrophobic effects combined with the hydrophilic effects within the hydrogel structure can be balanced through dangling side chains that mediates the hydrogen bonding that occurs between two separate hydrogel pieces or across a ruptured hydrogel. A dangling side chain is a hydrocarbon chain side chains that branch off of the backbone of the polymer. Attached to the side chain are polar functional groups. The side chains "dangle" across the surface of the hydrogel, allowing it to interact with other functional groups and form new bonds. The ideal side chain would be long and flexible so it could reach across the surface to react, but short enough to minimize steric hindrance and collapse from the hydrophobic effect. The side chains need to keep both the hydrophobic and hydrophilic effects in balance. In a study performed by the University of California San Diego to compare healing ability, hydrogels of varying side chain lengths with similar crosslinking contents were compared and the results showed that healing ability of the hydrogels depends nonmonotonically on the side chain length. With shorter side chain lengths, there is limited reach of the carboxyl group which decreases the mediation of the hydrogen bonds across the interface. As the chain increases in length, the reach of the carboxyl group becomes more flexible and the hydrogen bonds can mediated | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels However, when a side chain length is too long, the interruption between the interaction of the carboxyl and amide groups that help to mediate the hydrogen bonds. It can also accumulate and collapse the hydrogel and prevent the healing from occurring. Most self-healing hydrogels rely on electrostatic attraction to spontaneously create new bonds. The electrostatic attraction can be masked using protonation of the polar functional groups. When the pH is raised the polar functional groups become deprotonated, freeing the polar functional group to react. Since the hydrogels rely on electrostatic attraction for self-healing, the process can be affected by electrostatic screening. The effects of a change in salinity can be modeled using the Gouy-Chapman-Stern theory Double Layer . To calculate the Gouy-Chapmanm potential, the salinity factor must be calculated. The expression given for the salinity factor is as follows: These effects become important when considering the application of self-healing hydrogels to the medical field. They will be affected by the pH and salinity of blood. These effects also come into play during synthesis when trying to add large hydrophobes to a hydrophilic polymer backbone. A research group from the Istanbul Technical University has shown that large hydrophobes can be added by adding an electrolyte in a sufficient amount. During synthesis, the hydrophobes were held in micelles before attaching to the polymer backbone | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels By increasing the salinity of the solution, the micelles were able to grow and encompass more hydrophobes. If there are more hydrophobes in a micelle, then the solubility of the hydrophobe increases. The increase in the solubility lead to an increase in the formation of hydrogels with large hydrophobes. The surface tension (γ) of a material is directly related to its intramolecular and intermolecular forces. The stronger the force, the greater the surface tension. This can be modeled by an equation: Where ΔU is the energy of vaporization, N is Avogadro's number, and a is the surface area per molecule. This equation also implies that the energy of vaporization affects surface tension. It is known that the stronger the force, the higher the energy of vaporization. Surface tension can then be used to calculate surface energy (u). An equation describing this property is: Where T is temperature and the system is at constant pressure and area. Specifically for hydrogels, the free surface energy can be predicted using the Flory–Huggins free energy function for the hydrogels. For hydrogels, surface tension plays a role in several additional characteristics including swelling ratio and stabilization. Hydrogels have the remarkable ability to swell in water and aqueous solvents. During the process of swelling surface instability can occur. This instability depends on the thickness of the hydrogel layers and the surface tension | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels A higher surface tension stabilizes the flat surface of the hydrogel, which is the outer-most layer. The swelling ratio of the flat layer can be calculated using the following equation derived from the Flory–Huggins theory of free surface energy in hydrogels: Where λ is the swelling ratio, μ is the chemical potential, p is pressure, k is Boltzmann's constant, and χ and N are unitless hydrogel constants. As swelling increases, mechanical properties generally suffer. The surface deformation of hydrogels is important because it can result in self-induced cracking. Each hydrogel has a characteristic wavelength of instability (λ) that depends on elastocapillary length. This length is calculated by dividing the surface tension (γ) by the elasticity (μ) of the hydrogel. The greater the wavelength of instability, the greater the elastocapillary length of instability, which makes a material more prone to cracking. The characteristic wavelength of instability can be modeled by: formula_11 Where H is the thickness of the hydrogel. Some hydrogels are able to respond to stimuli and their surrounding environments. Examples of these stimuli include light, temperature, pH, and electrical fields. Hydrogels that are temperature sensitive are known as thermogels. Thermo-responsive hydrogels undergo reversible, thermally induced phase transition upon reaching either the upper or lower critical solution temperature. By definition, a crosslinked polymer gel is a macromolecule that cannot dissolve | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels Due to the polymeric domains created by crosslinking, in the gel microstructure, hydrogels are not homogenous within the solvent system in which they are placed into. Swelling of the network, however, does occur in the presence of a proper solvent. Voids in the microstructure of the gel where crosslinking agent or monomer has aggregated during polymerization can cause solvent to diffuse into or out of the hydrogel. The microstructure of hydrogel therefore are not constant, and imperfections occur where water from outside of the gel can accumulate these voids. This process is temperature dependent, and solvent behavior depends on whether the solvent-gel system has reached, or surpassed, the critical solution temperature (LCST). The LCST defines a boundary between which a gel or polymer chain will separate solvent into one or two phases. The spinodial and binodial regions of a polymer-solvent phase diagram represent the energetic favorability of the hydrogel becoming miscible in solution or separating into two phases. encompass a wide range of applications. With a high biocompatibility, hydrogels are useful for a number of medical applications. Areas where active research is currently being conducted include: Hydrogels are created from crosslinked polymers that are water-insoluble. Polymer hydrogels absorb significant amounts of aqueous solutions, and therefore have a high water content. This high water content makes hydrogel more similar to living body tissues than any other material for tissue regeneration | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels Additionally, polymer scaffolds using self-healing hydrogels are structurally similar to the extracellular matrices of many of the tissues. Scaffolds act as three-dimensional artificial templates in which the tissue targeted for reconstruction is cultured to grow onto. The high porosity of hydrogels allows for the diffusion of cells during migration, as well as the transfer of nutrients and waste products away from cellular membranes. Scaffolds are subject to harsh processing conditions during tissue culturing. These include mechanical stimulation to promote cellular growth, a process which places stress on the scaffold structure. This stress may lead to localized rupturing of the scaffold which is detrimental to the reconstruction process. In a self-healing hydrogel scaffold, ruptured scaffolds have the ability for localized self-repair of their damaged three-dimensional structure. Current research is exploring the effectiveness of using various types of hydrogel scaffolds for tissue engineering and regeneration including synthetic hydrogels, biological hydrogels, and biohybrid hydrogels. In 2019, researchers Biplab Sarkar and Vivek Kumar of the New Jersey Institute of Technology developed a self-assembling peptide hydrogel that has proven successful in increasing blood vessel regrowth and neuron survival in rats affected by Traumatic Brain Injuries (TBI) | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels By adapting the hydrogel to closely resemble brain tissue and injecting it into the injured areas of the brain, the researchers’ studies have shown improved mobility and cognition after only a week of treatment. If trials continued to prove successful, this peptide hydrogel may be approved for human trials and eventual widespread use in the medical community as a treatment for TBIs. This hydrogel also has the potential to be adapted to other forms of tissue in the human body, and promote regeneration and recovery from other injuries. Synthetic Hydrogels: Polyethylene glycol(PEG) polymers are synthetic materials that can be crosslinked to form hydrogels. PEG hydrogels are not toxic to the body, do not elicit an immune response, and have been approved by the US Food and Drug Administration for clinical use. The surfaces of PEG polymers are easily modified with peptide sequences that can attract cells for adhesion and could therefore be used for tissue regeneration. Poly (2-hydroxyethyl methacrylate) (PHEMA) hydrogels can be combined with rosette nanotubes (RNTs). RNTs can emulate skin structures such as collagen and keratin and self-assemble when injected into the body. This type of hydrogel is being explored for use in skin regeneration and has shown promising results such as fibroblast and keratinocyte proliferation. Both of these cell types are crucial for the production of skin components | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels Biological Hydrogels: Biological hydrogels are derived from preexisting components of body tissues such as collagen, hyaluronic acid (HA), or fibrin. Collagen, HA, and fibrin are components that occur naturally in the extracellular matrix of mammals. Collagen is the main structural component in tissues and it already contains cell-signaling domains that can promote cell growth. In order to mechanically enhance collagen into a hydrogel, it must be chemically crosslinked, crosslinked using UV light or temperature, or mixed with other polymers. Collagen hydrogels would be nontoxic and biocompatible. Hybrid Hydrogels: Hybrid hydrogels combine synthetic and biological materials and take advantage of the best properties of each. Synthetic polymers are easily customizable and can be tailored for specific functions such as biocompatibility. Biological polymers such as peptides also have adventitious properties such as specificity of binding and high affinity for certain cells and molecules. A hybrid of these two polymer types allows for the creation of hydrogels with novel properties. An example of a hybrid hydrogel would include a synthetically created polymer with several peptide domains. Peptide-based self-healing hydrogels may be selectively grown onto nanofiber material which can then incorporated into the desired reconstructive tissue target. The hydrogel framework is then chemically modified to promote cell adhesion to the nanofiber peptide scaffold | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels Because the growth of the extracellular matrix scaffold is pH dependent, the materials selected must be factored for pH response when selecting the scaffolding material. The swelling and bioadhesion of hydrogels can be controlled based on the fluid environment they are introduced to in the body. These properties make them excellent for use as controlled drug delivery devices. Where the hydrogel adheres in the body will be determined by its chemistry and reactions with the surrounding tissues. If introduced by mouth, the hydrogel could adhere to anywhere in the gastrointestinal tract including the mouth, the stomach, the small intestine, or the colon. Adhesion in a specifically targeted region will cause for a localized drug delivery and an increased concentration of the drug taken up by the tissues. Smart hydrogels in drug delivery: Smart hydrogels are sensitive to stimuli such as changes in temperature or pH. Changes in the environment alter the swelling properties of the hydrogels and can cause them to increase or decrease the release of the drug impregnated into the fibers. An example of this would be hydrogels that release insulin in the presence of high glucose levels in the bloodstream. These glucose sensitive hydrogels are modified with the enzyme glucose oxidase. In the presence of glucose, the glucose oxidase will catalyze a reaction that ends in increased levels of H | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels These H ions raise the pH of the surrounding environment and could therefore cause a change in a smart hydrogel that would initiate the release of insulin. Although research is currently focusing on the bioengineering aspect of self-healing hydrogels, several non-medical applications do exist, including: Dangling type side chain self-healing hydrogels are activated by changes in the relative acidity of solution they are in. Depending on user specified application, side chains may be selectively used in self-healing hydrogels as pH indicators. If a specified functional group chain end with a low pKa, such as a carboxylic acid, is subject to a neutral pH conditions, water will deprotonate the acidic chain end, activating the chain ends. Crosslinking or what is known as self-healing will begin, causing two or more separated hydrogels to fuse into one. Research into the use self-healing hydrogels has revealed an effective method for mitigating acid spills through the ability to selectively crosslink under acidic conditions. In a testing done by the University of California San Diego, various surfaces were coated with self healing hydrogels and then mechanically damaged with 300 micrometer wide cracks with the coatings healing the crack within seconds upon exposure of low pH buffers. The hydrogels also can adhere to various plastics due to hydrophobic interactions. Both findings suggest the use of these hydrogels as a sealant for vessels containing corrosive acids | https://en.wikipedia.org/wiki?curid=39638268 |
Self-healing hydrogels No commercial applications currently exist for implementation of this technology. Drying of hydrogels under controlled circumstances may yield xerogels and aerogels. A xerogel is a solid that retains significant porosity (15-50%) with a very small pore size (1–10 nm). In an aerogel, the porosity is somewhat higher and the pores are more than an order of magnitude larger, resulting in an ultra-low-density material with a low thermal conductivity and an almost translucent, smoke-like appearance. | https://en.wikipedia.org/wiki?curid=39638268 |
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