Selective adsorption of amphiphilic block copolymers on weak polyelectrolyte multilayers

In this study, an amphiphilic block copolymer, polystyrene-block-poly(acrylic acid) (PS-PAA), was adsorbed from tetrahydrofuran (THF) solution onto self-assembled weak polyelectrolyte multilayer surfaces of poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH). The short hydrophilic PAA block adsorbs to the multilayer surface as an anchor block and the long hydrophobic PS block then dangles out from the surface. Several different PAA/PAH multilayer systems generated by controlling the processing pH conditions were investigated in an attempt to find the optimal multilayer platforms for PS-PAA adsorption. We found that PS-PAA adsorption in this system is driven by mostly secondary interactions such as hydrogen-bonding. By regulating the nature of the multilayer surfaces, we were able to manipulate multilayer platform surfaces to be either highly promoting or highly blocking for PS-PAA adsorption. In the former case, contact angle measurements showed that, upon PS-PAA adsorption, a hydrophilic multilayer surface turned into a hydrophobic surface with contact angle values similar to those of a pure PS surface.