Structural studies of ideal organic-inorganic nanocomposites by high resolution diffractometry and NMR spectroscopy techniques

Hybrid organic-inorganic materials, silica-poly(ethylene glycol) (PEG) blen ds, were prepared by the sol-gel process from mixtures of tetraethoxysilane and PEG of low molecular mass. The synthesis scheme (acidic [HCl] or nucle ophilic [NH4F] catalysis) influences the structure of these materials and c onsequently their properties. Two different methods were used to investigat e the structure of these blends: a) X-ray diffraction techniques; b) (2)9Si NMR spectroscopy. A new x-ray diffractometry technique identifies precise interference functions and radial distribution functions of these blends. T he comparison of predicted radial distribution functions of the Bell and De an's physical model refined by Gaskell with the radial distribution functio n obtained from this technique is implemented to identify the structure of these blends. Analysis by amorphography has identified the existence of SiO 2 silica grains and provides only about the positional disorder of these gr ains in continuum random network. The NMR spectroscopy discriminates the di fferent silicon sites and demonstrates the changes of the morphology and st ructure when the nature of the catalyst is modified. These results indicate that the structure of non-crystalline SiO2 aggregates inside nanocomposite s differs from fused glass by their compositional disorders. These nanocomp osites could be described as an agglomerate of SiO2 objects with the pores filled by disordered polymer chains. When these materials are obtained unde r acidic conditions, the polymer chains are linked to the SiO2 grains formi ng an ideal composite. (C) 1999 Kluwer Academic Publishers.