Physics

NONCONTACT DETERMINATION OF SURFACE TENSION IN A SMALL FLUID SAMPLE BY LASER INTERFEROMETRY, C. Pawlak, D. Eivins, F. Behroozi*, University of Northern Iowa, Department of Physics, Cedar Falls, IA 50614, behroozi@uni.edu

We describe a non-contact method for determining the surface tension of a small fluid sample. The method exploits standing wave patterns on the surface of a fluid in a cylindrical well of volume less than 2 cm3. To generate the waves on the surface of the fluid, the well is driven by a piezoelectric transducer. The wave amplitude is monitored by a miniature laser interferometer as the driving frequency is increased. When the system is driven at a resonant frequency, the amplitude of the wave attains a maximum. The experimentally measured resonance frequencies and the associated wave numbers are then used in the dispersion relation to determine the surface tension of the fluid. Any curvature of the fluid surface increases the effective radius of the well. By plating the well with gold, we obtain a flat fluid surface. Surface tension data on pure water, water with 5% acetone, water with 10% acetone, and water with 20% glycerol are presented to show the effectiveness of this system in measuring the surface tension of liquids with a wide range of viscosity and surface tension.