Pervaporation performance of polystyrene membrane surface with perfluoroalkyl groups

Research on the effect of various chemical groups on the pervaporation performance of membranes was very important for understanding the separation phenomenon. In this article, a polystyrene membrane with CF 3 groups on its surface was prepared by casting normal polystyrene (PS‐H) solution with small‐molecular‐weight α,ω‐fluoroalkyl‐terminated polystyrene (S‐PS‐(CF 3 ) 2 ) on a glass plate. The amount of CF 3 groups on the surface was adjusted by changing S‐PS‐(CF 3 ) 2 content, which was documented by X‐ray photoelectron spectroscopy analysis, surface energy, and contact angle measurements. The effect of S‐PS‐(CF 3 ) 2 content on separation performance of S‐PS‐(CF 3 ) 2 /PS‐H blend membranes for ethanol/water mixture was investigated. The results showed that water concentration in the permeate decreased with increasing S‐PS‐(CF 3 ) 2 content; however, the permeation rate did not change until the S‐PS‐(CF 3 ) 2 content was increased to 1 wt %. The reason for this was attributed to the fact that a small amount of S‐PS‐(CF 3 ) 2 enables a simple surface modification of the membrane keeping its inner structure relatively unchanged. This was confirmed by swelling degree measurements and other experiments. Comparison with our previous work showed that the CF 3 groups on the surface lowers the water permselectivity of the polystyrene membranes, whereas the COOH groups enhance the water permselectivity. However, neither hydrophobic CF 3 nor hydrophilic groups on the membrane surface appeared to have any influence on flux. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007