Influence of the aminothiol structure on pervaporation dehydration of poly(thiol ester amide) composite membranes

In this study, poly(thiol ester amide) composite membranes were prepared via interfacial polymerization by reacting trimesoyl chloride (TMC) with 4-aminobenzenethiol (ABTH) or 2-aminoethanethiol (AETH) on the surface of a modified polyacrylonitrile (mPAN) membrane (ABTH–TMC/mPAN and AETH–TMC/mPAN). Pervaporation separation of an aqueous ethanol solution with poly(thiol ester amide) composite membranes was investigated as a function of aminothiol structure. To correlate variations in the free volume of poly(thiol ester amide) active layers with pervaporation performance, positron annihilation spectroscopy (PAS) experiments were performed with a variable mono-energy slow positron beam. The affinity of the poly(thiol ester amide) active layer for an aqueous ethanol solution increased upon introduction of a phenyl ring onto the poly(thiol ester amide) backbone. The active layer of AETH–TMC/mPAN composite membranes was thicker and possessed smaller pores (τ3) and a lower concentration (I3) of free volume than the active layer of ABTH–TMC/mPAN composite membranes did. Solution effects dominated the separation behavior of hydrated ethanol in all poly(thiol ester amide) composite membranes. Furthermore, ABTH–TMC/mPAN composite membranes possessed a higher permeation rate than AETH–TMC/mPAN membranes.