The salt-, pH- and oxidant-responsive pervaporation behaviors of weak polyelectrolyte multilayer membranes

The layer-by-layer (LbL) assembled polyelectrolyte multilayer has recently been recognized as a new class of promising membrane material for various separation uses. However, there is a lack of understanding about the influences of separation mixtures on the adsorbed polyelectrolytes. Therefore, clear understanding on it would be very important for the design and application of a type of new functional composite membrane. In this paper, the multilayer of weak polyelectrolytes polyethyleneimine and polyacrylic acid was constructed onto a hydrolyzed hollow fiber polyacrylonitrile support membrane under a negative pressure condition. The salt-, pH- and oxidant-responsive pervaporation behaviors of polyelectrolyte multilayer membranes were evaluated by post-treating with sodium chloride, hydrochloric acid, sodium hydroxide and sodium hypochlorite aqueous solutions, respectively. The pervaporation performances for separation of ethanol/water were compared before and after post-treatments. Scanning electron microscopy and atomic force microscopy confirmed the microtopographical changes of membrane surfaces. Optical microscopy was also used to real-time observe surface morphologies of polyelectrolyte multilayers deposited on the quartz substrates. Finally, the comparison of zeta potential values of inner surface before and after post-treatment also demonstrated the changes of surface electrical property.