Reversible and irreversible evincing of Rehbinder effect in polymer systems

Abstract

Changing polyethyleneterephthalate film properties by means of their treatment with solvents comprising crystallizing and non-crystallizing components has been studied. It has been found that under the influence of the solvent a microheterogeneous defect structure (and in a narrow range of modifying solvent concentrations, microporous structure) appears. Studying the structure is of a special interest because it opens up an opportunity to intensify transmembrane fluxes. The cause of micropore appearance is developing of internal stretching tensions locally exceeding material’s strength lowered by the adsorption active medium. Permeability and selectivity autooscillations have been detected in the process of evaporation of binary mixtures of low molecular weight solvents through an asymmetric polyvinyltrimethylsilane membrane. The autooscillations were caused by a reversible evincing of Rehbinder effect: periodic emergence and collapse of micropores in the membrane’s active layer. Reversible structural transitions play the role of a feed-back relay controlling switching the fluxes in the pores on and off. Conductometric measurements of swelling of chitosan in water vapour have been carried out. Gradual evolution of kinetic instabilities and macrofluctuations (stochastic autooscillations) of local (belonging to infinite clusters) sorbate concentrations were observed as variations of electrical current. The phenomenon is connected with a course of relaxation processes resulting in induced porosity genesis. There were no macrofluctuations if the polymer had a relaxed structure. Wavelet analysis was applied for characterization of the swelling dynamics.