Measurement of the interface tension of smectic membranes in water.

A simple method is proposed to measure the interfacial tension of a smectic liquid crystal (LC) in freely suspended film geometry in aqueous environment. The method is based upon the evaluation of the deformation of smectic bubbles by the buoyancy of a trapped air volume. The advantages over classical suspended smectic droplet experiments in water are the considerably shorter equilibration times, and most important, the much larger density differences between the fluids. The latter allow a much more accurate force determination. Bulk elastic force contributions can be practically neglected in the thin smectic films. Values for a smectic C mixture of two disubstituted phenylpyrimidines are reported.