SURFACE-TENSION FROM PENDANT DROP CURVATURE

A basic property of the curvature of pendant drops and computer spline s have been used to develop a simple and highly reliable method for th e determination of interfacial tension of fluid-fluid interfaces using a drop shape technique. Solutions to the Laplace-Young equation for p endant drops predict a linearly varying curvature as a function of ele vation. Plotting the mean curvature of the pendant drop versus elevati on renders a straight line with slope a = -DELTArho g/sigma, where DEL TArho is the difference in densities of the two fluids, g is the accel eration of gravity, and sigma is the interfacial tension. Numerical di fferentiation of experimental data, however, is nearly impossible when any level of noise is present. Computer-generated spline functions we re used to represent the experimental data to a prescribed degree of s moothness. In turn, derivatives of the spline functions provide an acc urate and reliable way to determine the curvature of the drop image. T he method has been tested with the computer-generated image of a water drop and with experimental data for five hydrocarbons as well as decy l alcohol.