Membrane structure and permeation properties of poly(vinyl chloride)/liquid crystal composite membrane

Abstract

Abstract A series of polymer/liquid crystal composite membranes, at several weight ratios, was prepared casting from a tetrahydrofuran solution of poly(vinyl chloride) (PVC) with N ‐(4‐ethoxy‐benzylidene)‐4′‐butylaniline (EBBA). From the thermal analysis, microscopic observation, mechanical property, and gas permeation studies, the properties for a series of PVC/EBBA composite membranes were derived. DSC showed that PVC and EBBA were quite miscible and EBBA in composite membranes at below 30 wt % was molecularly dispersed without forming crystal domains. Morphological observations exhibited that EBBA molecules interpenetrated in a continuous phase among the 3‐dimensional spongy networks of PVC matrix in the case of the 40/60 (PVC/EBBA, in wt %) composite membrane. Stable retention of EBBA in the composite membrane and its high mechanical durability might arise from such an aggregation structure. The permeability coefficients to oxygen gas, P 02 and nitrogen one, P N2 through the 40/60 (PVC/EBBA) composite membrane showed a discontinuous jump with a several–tenfold increase in the vicinity of the crystal–nematic transition temperature T KN of EBBA. The magnitudes of P 02 and the separation factors P 02 / P N2 above T KN were of the order of 10 −9 cm 3 (STP) cm −1 s −1 cm Hg −1 and 2–3, respectively. The value of P 02 / P N2 reached a maximum just above T KN . The P 02 − P 02 / P N2 relationship above T KN exhibited an unusual behavior as P 02 / P N2 increased with an increase in P 02 .