I. Transition regions, line tensions and contact angles in soap films

Abstract

An analysis is given of the thickness profile of a circular soap film and its Plateau border. It shows that in principle the thickness as a function of the radial distance, h(r), for a single film, can provide details of the interaction free energy ΔF(h) over a large range of h. The transition region between film and Plateau border where h(r) rapidly changes from microscopic to macroscopic values contains most information. With a simple model of ΔF(h), the profile and extension of the transition region is calculated for some “first black” soap films.

It is shown that to complete the macroscopic description of a liquid sheet. a line tension must be introduced. A theoretical expression for this line tension is given and its physical meaning is discussed. Some values are calculated using the same ΔF(h) as before.