Dynamic light scattering is used to study the dependence of the aggregation kernel homogeneity A. on the aggregant concentration [HClj for aqueous gold sols. We find the cluster growth kinetics are well described by a powerlaw, R,p"-t', where R, » is the measured apparent radius, D the cluster fractal dimension, and z =1/(1 -A, ) for all aggregant concentrations. The values for the dynamic exponent z, and hence the homogeneity k, are functions of HC1 concentration. %'e find the larger HC1 concentrations yield a fast-aggregation regime characterized by A. = -0.6. Smaller HC1 concentrations yield a continuum of aggregation regimes characterized by homogeneities evolving from A. = -0.6 towards 1.0. Our results do not support the view that aggregation in gold colloids is based on two limiting regimes, diffusion-limited and reaction-limited aggregation.

The growth and morphology of crystals of hard colloidal spheres is monitored by a special photographic technique. Crystals are observed to grow in size and increase in number density, initially. This is followed by a decrease in size and an increase to saturation in the number density. During the growth stage the crystals evidence irregular rectangular shapes, and an internal substructure is evident within the larger crystals. The observed size decrease suggests a breakup of crystals to a length scale of the internal structure. A simple model for surface roughening, which has been used to classify crystal morphology, is examined for hard sphere crystals. Hard sphere crystals should be classified as “rough” and subject to growth instabilities. The length scale for simple planar and spherical instabilities is examined for hard sphere crystals and is found to be smaller than the observed length scales.

A detailed investigation of the molecular weight dependence of silica growth in in situ filled polydimethylsiloxane/tetraethylorthosilicate (PDMS/TEOS) materials was conducted using small angle neutron scattering (SANS). Composite materials were produced by using TEOS to simultaneously produce the glassy filler phase and to crosslink linear, hydroxyl terminated PDMS of variable molecular weight, M. Correlated domains of glassy filler were produced. The morphology of the in situ filled material showed a definite dependence on the molecular weight of the precursor polymer. The scale, R, of the glassy domains follows de Gennes' description of phase separation in a crosslinked system (R ∝ M1/2).

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