Abstract
Dynamic light scattering is used to study the dependence of the aggregation kernel homogeneity \ensuremath{\lambda} on the aggregant concentration [HCl] for aqueous gold sols. We find the cluster growth kinetics are well described by a powerlaw, ${R}_{\mathrm{app}\mathrm{\ensuremath{\sim}}{t}^{z/D}}$, where ${R}_{\mathrm{app}}$ is the measured apparent radius, D the cluster fractal dimension, and z=1/(1-\ensuremath{\lambda}) for all aggregant concentrations. The values for the dynamic exponent z, and hence the homogeneity \ensuremath{\lambda}, are functions of HCl concentration. We find the larger HCl concentrations yield a fast-aggregation regime characterized by \ensuremath{\lambda}\ensuremath{\simeq}-0.6. Smaller HCl concentrations yield a continuum of aggregation regimes characterized by homogeneities evolving from \ensuremath{\lambda}\ensuremath{\simeq}-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.
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