Pervaporation separation of alcohol/water mixtures using self-assembled polyelectrolyte multilayer membranes of high charge density

The alcohol/water separation of polyelectrolyte multilayer membranes of high charge density prepared upon electrostatic layer-by-layer (LBL) adsorption of cationic and anionic polyelectrolytes is described. Polyvinylamine (PVA) was used as the cationic polyelectrolyte, and polyvinylsulfonate (PVSu), polyvinylsulfate (PVS) and polyacrylate (PAA) were used as anionic polyelectrolytes; the separation was studied under pervaporation conditions. At low water content in the feed (<20 wt.%), the strongly hydrophilic PVA/PVSu membrane is best suited for separation, while at higher water content the less hydrophilic PVA/PAA membrane exhibits the best separation. Membranes prepared at pH 1.7 with no salt present in the polyelectrolyte solution exhibit a substantially worse separation capability than membranes prepared at pH 1.7 in the presence of NaCl, or at pH 6.8 in the absence of salt. Use of PAA of low molecular weight (m.w. 5000) leads to membranes of much lower total flux than use of PAA of molecular weight 250,000.