Relaxation experiments of polymeric systems confined in very narrow gaps

Abstract

A new way of investigating the relaxation processes of polymeric systems confined between solid surfaces is presented here. The test is based on draining experiments by means of a surface force apparatus and consists in monitoring the hydrodynamic force release following a drainage motion. Experiments carried out with solutions of high polymers exhibit two distinct relaxation processes. The longest one is connected to the relaxation of the chains adsorbed onto the solid surfaces and which are pinned in the area of closest distance between the solid surfaces. Its variations as a function of spacing are consistent with the bridging of some macromolecules. The fastest process is connected to the flow of the solvent molecules through the pseudonetwork formed by the adsorbed layers carried by the solid surfaces. These results have been compared favorably with those obtained by oscillatory measurements as far as relaxation time and viscosity are concerned. The accuracy of the experimental relaxation function is not sufficient for describing reasonably the viscoelastic behavior of the confined fluid. © 1996 John Wiley & Sons, Inc.