SURFACE FORCES IN FOAM FILMS FROM ABA BLOCK-COPOLYMER - A DYNAMIC METHOD STUDY

The thinning of foam films from aqueous solutions of an ABA triblock c opolymer of polyethylene oxide and polypropylene oxide (average molecu lar weight 14,000 g/mol) is studied experimentally. The dependence of the surface forces on him thickness is obtained by the dynamic method of Scheludko and Exerowa. The total surface force measured in foam fil ms (radius approximate to 60-70 mu m) from 10(-5) M (0.014 wt%) polyme r solution with 0.1 M NaCl is positive at thicknesses from about 800 A ngstrom down to 460 Angstrom. The electrostatic repulsion is negligibl e while the contribution of van der Waals attraction is small (within 15%). Therefore a positive surface force component predominates. Most probably it arises from steric interactions between the hydrophilic po lyethylene oxide tails of the polymer. The dynamic method appears to b e a suitable technique for exploring the stabilization of foam films f rom ABA copolymers.