Crystal Structures of Monodisperse Colloidal Silica in Poly(methyl acrylate) Films

Abstract

Dispersions of 22.3 vol % of 153 nm diam. silica particles coated with 3-(trimethoxysilyl)propyl methacrylate in liq. Me acrylate (MA) as 264-528 mm thick films in glass cells spontaneously order into colloidal crystals and Bragg diffract visible light from lattice planes parallel to the film plane. Photopolymn. of the MA gives elastomeric poly(Me acrylate) (PMA) films with retention of the cryst. order. Swelling the films with more MA and further polymn. give colloidal cryst. composite films with larger lattice spacings. The crystal structures are modeled as fcc. for the monomer dispersions and rhombohedral for the polymer films. Layer spacings obsd. in scanning electron micrographs (SEM) of microtomed PMA films are used to calc. the (111) spacings and the lattice parameter a of the model. The layer spacings correlate well with the diffraction wavelengths from optical spectra. Ultrasmall angle X-ray diffraction also was performed to demonstrate the three-dimensional cryst. order. The SEM and optical spectra also fit hcp. (hcp) or mixed rhombohedral and hcp structures. [on SciFinder (R)]