Composite Bilayer Polymer Membranes with Hydrophobic Layers

Bilayer composite membranes (CMs) are prepared by depositing a polymer layer onto track-etched polypropylene (PP) membrane by using plasma polymerization of hexamethyldisilazane (HMDSN). The chemical structure, wetting properties, and morphological characteristics of the prepared CMs are investigated. By depositing the plasma-polymerized polymer, we obtain CMs with two hydrophobic layers, of which one is the initial PP membrane, serving as a matrix. This layer has a water contact angle of 120°. The other layer, which was formed during plasma polymerization of HMDSN, contains nitrogen-containing functional groups, along with minor amounts of oxygen-containing, mainly carboxylic, groups. The water contact angle of this layer is ~98°. Deposition of a polymer film by plasma-assisted polymerization results in smoothing surface asperities of the initial (matrix) membrane, a considerable decrease in pore diameter, and alteration of pore shape; namely, the pores acquire an asymmetric (conical) profile.