Evaluation of liquid transport properties of hydrophobic polymers of intrinsic microporosity by electrical resistance measurement

Abstract

In this work, the electrical resistance method was used to get an insight of the liquid transport through the polymers with excess of fractional free volume. The dense films based on the first generation of polymers of intrinsic microporosity, disubstituted polyacetylenes PMP and PTMSP, were used; water-ethanol binary mixtures allowed to adjust the affinity of the liquid phase to selected polymers continuously. In this work, the liquid-membrane interaction was considered as a stepwise occupation of accessible free volume elements within the polymer, while the appearance of continuous (pseudo)liquid channels in the polymeric matrix, so-called percolation clusters, was required for formation of hydrodynamic liquid transport. Since the appearance of such percolation clusters might dramatically change the conductivity of hydrophobic materials, it was proposed to use the electrical resistance method to investigate the evaluation of selected polymers from being a barrier (water) to being permeable (ethanol) with respect to the liquid composition. To highlight the electrical resistance of the swollen films, all water/ethanol solutions contained NaCl (0.5 g/L). The steady-state values of liquid permeation, sorption/swelling, and electrical conductivity data were considered together and discussed. The electric resistance was significantly varied for 30 µm dense films of PMP (1–1300 kΩ) and PTMSP (0.15–910 kΩ) by the adjustment of ethanol content in water. The phase shift (25– 100,000 Hz) illustrated that the behavior of PTMSP and PMP membranes changed from mainly capacitive at low ethanol concentrations to the ion conductive as higher ethanol content. The very good quantitative agreement was found between the relative change of the membrane electrical resistance and the permeability as a function of the ethanol content in the liquid phase. Consequently, electrical resistance measurements could be used as an express method to determine the membrane permeability of low permeable materials, since the time required to get steady-state results was found to be much shorter for electrical resistance measurements than for permeability measurements.