Osmotic Stresses and Wetting by Polymer Solutions

Polymer solutions do not wet the substrate, even when the solvent is wetting. It is suggested here that it becomes difficult to squeeze polymer molecules into thin films found near the contact line due to adverse changes in the polymer entropy. Models are used to show that as the film thins a potential barrier is encountered due to the entropy changes in the polymer. This is observed in the calculated values of disjoining pressure as a function of film thickness. Equations arising from force balances are used to predict the contact angles in terms of a model disjoining pressure. the results can vary with the nature of constraints on the system, and care has been exercised to be faithful to the experiments reported earlier. Qualitatively, the dependence of the contact angles on various parameters are correctly predicted