Structure of nanometric silica clusters in polymeric composite materials

Composite films were prepared from nanometric silica suspension and poly(vinyl alcohol) (PVA) solution. Both were mixed at increasing silica contents and left until complete evaporation of the solvent. Small angle neutron scattering (SANS) and transmission electron microscopy (TEM) were used to characterize the local and mean particle distribution of silica particles in the film. The interaction between the polymer and the surface was characterized through an adsorption isotherm. The SANS results were processed within the Percus-Yevick approximation. At a given drying stage, the colloidal system undergoes a microphase separation and submicron size clusters are produced. Both SANS and TEM showed the presence of dense and well-ordered clusters in the dry film. The size of the clusters and the surface-to-surface distance between the silica primary particles within the clusters both depend on the initial ionic strength.