AXISYMMETRICAL DROP SHAPE-ANALYSIS AS A FILM BALANCE

A pendent drop experiment is used to demonstrate the possibility of using a surface tension measurement technique, axisymmetric drop shape analysis-profile (ADSA-P), as a film balance. Owing to the fact that both the values of the surface tension and the surface area are outputs of ADSA-P, a continuous measurement of the surface tension as a function of the surface area is possible using a motor-driven syringe to change the drop volume. In the case of an insoluble monolayer on the drop surface, the surface tension as a function of the surface area constitutes de facto film balance measurements. As an illustration, such ''film-balance'' measurements on a monolayer of octadecanol are presented and compared with conventional him balance measurements. It is shown that the results found by ADSA-P are in good agreement with those from the conventional film balance measurements. As a film balance, ADSA-P offers a range of possibilities which are discussed briefly.