STRUCTURAL MODELS FOR HOMOGENEOUS ORGANIC-INORGANIC HYBRID MATERIALS - SIMULATIONS OF SMALL-ANGLE X-RAY-SCATTERING PROFILES

Two morphological models have been proposed to describe small-angle x-ray scattering from organic-inorganic composite (OIC) materials. The first model invokes the idea of a liquid-like arrangement among noninterpenetrating fractal clusters, and the second employs an empirical correlation function that would be expected for a bicontinuous two-phase (B2P) picture with the inorganic portion exhibiting fractal characteristics. Simulated scattering profiles have been generated for direct comparison with experimental data. The samples studied were a triethoxysilane-endcapped bisphenol A epoxide resin (EAS) reacted in the presence of tetraethoxysilane (TEOS) under slightly basic conditions, and a random trimethoxysilane-functionalized copolymer of poly(methyl methacrylate) (MMA-TMS) with added tetramethoxysilane (TMOS), reacted in an acidic medium. Each morphology model qualitatively simulates the broad scattering maximum and limiting high-angle slope commonly seen in SAXS profiles. It is concluded that the inorganic phase in the EAS hybrid exhibits particle-like characteristics at length scales less than approximately 250 Angstrom, acid the organic and inorganic components are bicontinuous at larger distances. The MMA-TMS composite is better described by bicontinuous organic and inorganic phases with a periodic fluctuation of about 40 Angstrom. The scattering maximum arises either from the mean separation of pal-tides or a dominant wavelength in a concentration fluctuation, similar to that observed for spinodal decomposition. In either case, the SAXS peak position is related to the distance between junction points of the crosslinked organic polymer. (C) 1995 John Wiley and Sons, Inc.