Intercation Forces in Foam Films

Foam Films Stabilized by A-B-A Block Copolymers. Brush-to-Brush Interacrtion 

A general test for the presence of electrostatic interaction in a film is the influence of the electrolyte concentration. The equivalent film thickness h of foam films from Pluronic F108 aqueous solutions decreases with increasing electrolyte concentration [CgiJ [4]. Above the so-called critical concentration, Ufi — 3x10 mol dm NaCl, h remains constant. There is a plateau in the H ,(Cei) curve. The concentration Cei cr distinguishes the electrostatic interaction from the steric interaction and shows the transition between them. 

Direct experimental measurement of disjoining pressure vs thickness isotherms, Il(h ), is very informative in establishing surface forces in films from polymeric 

For PEO-PPO-PEO triblock copolymers it was found that the poly(ethylene oxide) chain is in the brush configuration ifD Rj D is the lateral distance between the chains, Rj is the radius of gyration). When h 2hi a brush-to-brush interaction appears, which can be described by the scaling theory of de Gennes [39,40[, according to which the steric disjoining pressure is given by 

7 X 10 mol dm F108 + mol dm NaCl aqueous solution [4], with Cei being 

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