Structure of latex-silica nanocomposite films:: A small-angle neutron scattering study

We report on the synthesis and structure of silica-filled latex films. The main stage of the synthesis consists of physicochemical manipulations of colloidal solutions of nanosilica and nanolatex beads, followed by drying and filmification. Hence, no mechanical energy which might contribute to building or destruction of aggregates of silica beads is supplied to the samples. We have analyzed the structure of the resulting filled latex films by means of small-angle neutron scattering. The scattered intensity varies enormously with the physicochemical parameters, indicating considerable structural modifications. To rationalize these results, we present a unified description of the data which successfully accounts for the main characteristics of the scattered intensity: the form factor of beads at large q vectors, the position of the intra- and interaggregate structure factor peaks, the small-q upturn observed in some cases, and the overall intensity in absolute units. This allows us to quantify the degree of aggregation of the silica in the matrix. It is found that the latter can be varied in a systematic manner by changing pH, silica volume fraction, and quantity of added salt. In one extreme case, for example, the aggregation number changes by a factor of about 1000 at constant silica volume fraction.