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

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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, P02 and nitrogen one, PN2 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 TKN of EBBA. The magnitudes of P02 and the separation factors P02/PN2 above TKN were of the order of 10−9 cm3 (STP) cm−1 s−1 cm Hg−1 and 2–3, respectively. The value of P02/PN2 reached a maximum just above TKN. The P02 − P02/PN2 relationship above TKN exhibited an unusual behavior as P02/PN2 increased with an increase in P02.