Functional Nanocavity Arrays via Amphiphilic Block Copolymer Thin Films

Abstract

The amphiphilic block copolymer polystyrene-block-poly(acrylic acid) (PS-b-PAA) forms micelles in toluene that can be cast onto a planar substrate to create quasi-hexagonal arrays of spherical PAA domains in a PS matrix. Treatment of these ultrathin films with an appropriate selective solvent swells the PAA domains and fractures open (cavitates) the PS matrix, thereby exposing the PAA chains to solution. Here we have investigated the conditions required for this cavitation process to occur and the end-state polymer morphology of close-packed films of PS-b-PAA micelles following treatment with a series of short alkyl chain alcohols or aqueous solutions of varying pH and ionic strength. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were employed to characterize the morphologies of the precursor and solvent-treated films. In addition to the effects of solvent conditions, we show that the cavitation process is influenced by the molecular weight of the PS block and is thermally rever...