Amphiphilic Block Copolymer Films: Phase Transition, Stabilization, and Nanoscale Templates

A morphological transition of asymmetric poly(styrene-b-acrylic acid) (PS-b-PAA) films is observed by in situ scanning probe microscopy (SPM) in aqueous media. Upon initial exposure to buffer solution at pH 74, spherical PAA domains swell through a glassy PS surface layer to form negatively charged mushroom caps. With further exposure, the PAA caps coalesce to produce a smooth, highly wettable surface. However, if films are exposed to a buffer Solution containing 3-aminopropyltriethoxysilane (APTES) for I h, the PAA domain swelling is greatly reduced and the mushroom caps stabilize at a diameter of 33 nm. This stabilization results from a cross-linking reaction between PAA and APTES, which also converts the PAA domains from a net negative to net positive charge. By varying molecular weights of PAA block in PS-b-PAA, the feature size and spacing can he tuned. To demonstrate air application for this template with positively charged domains, a cytoskeletal filament. F-Actin with a net negative charge, is organized on the PS-b-PAA template via electrostatic interactions under physiological conditions. F-Actin shows a tendency to align along the modified PAA mushroom caps.