Conversion of colloidal crystals to polymer nets: Turning latex particles inside out

Copolymer latexes of styrene and 5-10 mol % 2-hydroxyethyl methacrylate (HEMA) with narrow polydispersity produce films of colloidal crystals on glass by evaporative deposition. Treatment with vapors of styrene or toluene followed by drying transforms the morphology of the film to a porous polymer net with hexagonally ordered holes on the surface. We propose that the conversion takes place by swelling of styrene into the polystyrene-rich cores of the particles, which expand and engulf the polyHEMA-rich shells, leaving the polystyrene-rich phase on the surface and the polyHEMA-rich phase inside after the styrene evaporates. Evidence for the polyHEMA-rich surface of the colloidal crystal and the polystyrene-rich surface of the net is provided by contact angle measurements that show the surface of the net to be more hydrophobic than the colloidal crystal and by X-ray photoelectron spectroscopic measurements that show a higher oxygen content on the surface of the colloidal crystal than on the surface of the net.