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 (0.5g/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 (25-100000 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 2 steady-state results was found to be much shorter for electrical resistance measurements than for permeability measurements.

Transport Properties of Liquid Phase Percolation Cluster in Highly Permeable Glassy Polymers

“…The critical conductor fraction was determined by the Monte Carlo methods (Kirkpatrick, 1973;Vysotskii et al, 1995;McLachalan et al, 1993;Hsu et al, 1980), and it was found that this value is related to the size and the orientation of particles of both phases, and for three-dimensional systems. However, in experiments with a strong asymmetry of the conducting and non-conducting forms, the values can be even larger (Kirkpatrick, 1973;Hsu and Berzins, 1985;Yushkin et al, 2018). Thus, the values obtained agree with the literature data.…”

“…This created the observed hysteresis. It should also be noted that previously hysteresis phenomena were observed in various polymers with internal microporosity (Yushkin et al, 2018), and in hydrophilic cellophane .…”

“…The liquid permeability coefficient and the electrical conductivity are provided by the liquid phase inside the membrane and, therefore, the electrical resistance is a good criterion for predicting the transport properties of the membrane. As in (Yushkin et al, 2018), a hysteresis of the membrane properties was observed when the ethanol concentration in the surrounding solution changed upward and downward. One of the mechanisms of the observed hysteresis is related to the fact that during the initial filling of the free volume elements, the largest free volume elements are filled first, while the percolation cluster is formed at the ⁓30% ethanol concentration when the isolated elements begin to merge into a network after the smaller elements fill up.…”

“…The active membrane area in the cell was 1 cm 2 . It was shown in (Yushkin et al, 2018) that after the membrane is placed in the solution, it takes less than three hours to reach the stationary values of the membrane electrical conductivity. The membrane was placed in the solution 24 hours before measuring the impedance characteristics, and this ensured that the measured values were stationary.…”

The immobilisation and reactivity of Fe(CN)63−/4− in an intrinsically microporous polyamine (PIM-EA-TB)

“…1). The effects of "fractional free volume" in rigid microporous polymer structures on ion transport and conductivity have been considered [34]. In PIM-EA-TB, there are "free volume elements" providing multiple amine site, which after protonation allow anion binding into "cavities".…”