FOAM AND WETTING FILMS FROM AMPHIPHILIC BLOCK COPOLYMERS: ISOELECTRIC STATE AND STABILITY$AFOAM AND WETTING FILMS FROM AMPHIPHILIC BLOCK COPOLYMERS ISOELECTRIC STATE AND STABILITY

摘要

Using microinterferometric method the foam and wetting films from PEO-PPO-PEO triblock copolymers Syn-peronic P85 and F108 were studied under the identical conditions. The background electrolyte concentration range where DLVO forces (electrostatic and van der Waals) and non-DLVO forces (steric) act in the films was determined. It is unanimously shown through the film thickness vs. pH dependence that electrostatic interactions (i.e., the potential and the surface charge) in foam and wetting films from non-ionic polymer surfactants arise from preferential adsorption of OH~ ions at the solution/air interface. The films obtained below the critical pH values are sterically stabilized, i.e., decreasing pH induces a transition from electrostatic to steric stabilization. Three-layer models are designed for both types of films that allow calculating the electrostatic disjoining pressure, Oel. The values of % potential of the foam film are used to calculate nel in wetting films. A relation between isoelectric state of foam and wetting films and their stability is found to exist in the range of pH corresponding to electrostatic stabilization. Methastable films, film rupture or the transition to sterically stabilized films were also found.