Web Release Date: February 16,
Functional Nanocavity Arrays via Amphiphilic Block Copolymer Thin Films
and
Department of Chemical Engineering, Department of Materials Science and Engineering, and Department of Biological Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139
Received August 28, 2007
Revised Manuscript Received November 29, 2007
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 reversible. Following cavitation, the nanopatterned regions of exposed PAA are available for conjugation chemistry, demonstrated here through selective linking of a fluorescently labeled protein.
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