Comparison of different polymer-like structures in the confined geometry of foam films

Recent studies by a thin him balance of free standing thin liquid films con taining polyelectrolytes result in jump-like discontinuities in the film th ickness with increasing pressure. These jumps correspond to an oscillation of the disjoining pressure. They are correlated to a network-like chain str ucture in the film similar to that one found in aqueous semi-dilute polyele ctrolyte solutions. The results presented in this paper show that the appli cation of the theory for polyelectrolytes in bulk solutions to the behaviou r in the confined geometry of foam films is generally valid. A surfactant w hich forms worm-like micelles and two different polyelectrolytes were studi ed. Though the systems are very different, in all cases the oscillation per iod of the disjoining pressure scales as 1/root(c) over bar with the concen tration c. It is assumed that there is a network of polyelectrolyte chains and worm-like micelles respectively in the foam film and that the oscillati on period corresponds to the meshsize (correlation length) of the network. The correlation length calculated by the theory for semi-dilute polyelectro lyte solutions corresponds to the measured jump size at a fixed polyelectro lyte concentration. (C) 2001 Elsevier Science B.V. All rights reserved.