Fabrication and characterization of micro-patterned PDMS composite membranes for enhanced ethanol recovery

Bio-ethanol recovery via pervaporation process has drawn growing attention in the past few decades, however, its large-scale industry application remains limited due to the relatively low separation efficiency, especially in flux. In view of this, surface patterned nonporous PDMS (Polydimethylsiloxane) composite membranes with enhanced ethanol recovery efficiency were fabricated in this work. Line and space pattern was first printed on two-layer PVDF (Polyvinylidene fluoride) substrate using phase separation micromolding followed by modified immersion precipitation. And then PDMS solution prepared with three kinds of crosslinking agents (TEOS, Tetraethyl orthosilicate; VTES, Triethoxyvinylsilane; p-TTES, p-tolyltriethoxysilane) were cast atop the as-prepared patterned substrate as selective layer. Morphology, topography and surface chemistry were thoroughly characterized and results indicated that PDMS cross linked with TEOS showed the largest pattern size, while for membranes prepared with VTES and p-TTES, pattern size appeared to be smoothed. This can be mainly ascribed to the higher steric effect introduced by vinyl and phenmethyl groups, which increased the rigidity of polymer and thereby reduced the pattern size. Pervaporation performance for both patterned and non-patterned composite membranes under varied feed concentration and temperature were also evaluated. Evidence supported that permeate flux of patterned membranes cross linked with TEOS reached 977.73 g m⁻² h⁻¹ (45 °C, 2 wt% ethanol concentration) and are generally 2.11 times as high as that of non-patterned one. In addition, although increased the permeate flux, surface patterning exerted no adverse effect on membrane selectivity. The overall findings of this work provide a promising platform for nonporous composite membrane preparation to achieve high permeate flux without losing selectivity.