TRANSPORT PROPERTIES OF LIQUID PHASE PERCOLATION CLUSTER IN HIGHLY PERMEABLE GLASSY POLYMERS

Abstract

Porosity, permeability, and conductivity of PTMSP membranes in ethanol-water mixtures were determined by analyzing the impedance characteristics. The critical volume fraction of porosity at which through conductivity channels are formed was calculated. When the alcohol content in the solution increases, it was 0.29; when it decreases, it was 0.17. The obtained dependencies indicate that the transfer of matter in the membrane occurs the liquid phase elements, forming a percolation cluster as the amount of sorbed liquid increases. The hysteresis effect was observed in the measured values of porosity, permeability, conductivity, and capacity. The porous structure of a dry PTMSP membrane consists of free volume elements that are unconnected to each other. At ⁓30% alcohol concentration, through channels, begin to form, connecting both sides of the membrane. In this case, both permeability and electrical conductivity increase as a power function, in contrast to the porosity that increases linearly. Lichtenecker and Rother’s formula helped to calculate the volume fractions of the conducting and non-conducting phases in the system. The obtained values of the amount of liquid in the membrane at various spatial arrangements of the channels made it possible to establish the structure of the liquid-filled channels. The best agreement with the experimental values was obtained for the chaotic structure. This is consistent with the existing ideas about the structure of the studied membranes and confirms the assumption that the percolation cluster is formed from free volume elements filled with the liquid phase. The observed low values of the zeta potential and, consequently, the low values of the electrostatic component of the wedging pressure indicate that the increase in the size or the number of transport channels is associated with non-electrostatic forces.