On the dynamics of mobilization in swelling-dissolving polymeric systems

Abstract

The dynamics of the swelling-dissolution process in a rubbery polymer has been probed at a microscopic level for the first time by doing in situ NMR measurements. Some preliminary experiments on swelling-dissolution of polyisoprene have been performed. The appearance of an intermediate plateau in the mobility vs time plot in this system is highly suggestive of "pseudoequilibrium" swelling, which persists for a surprisingly long time before any substantial dissolution can take place. Based on these microscopic observations, a mathematical model for the swelling-dissolution process has been developed which treats the swelling process and the dissolution process as distinct decoupled processes. "Disengagement" of polymer chains at the interface due to the hydrodynamic forces on the polymer chains dangling into the liquid has been postulated to be responsible for the increased dissolution rates under shearing conditions. The simple model developed is able to correctly predict the existence of the plateau under stagnant conditions as well as the disappearance of the plateau in a hydrodynamic field.