Experimental study of colloidal aggregation in two dimensions. I. Structural aspects

Abstract

The morphology of structures formed during the two-dimensional aggregation of colloidal particles at a liquid surface has been studied. The aggregation was induced by adding ${\mathrm{CaCl}}_2$ solution to the aqueous subphase, the electrolyte concentration being varied to change the growth conditions. Under all conditions the clusters displayed self-similarity, the fractal dimension D determined by three independent methods concurring. For low subphase molarities the measured values of D were in accord with predictions for reaction-limited cluster-cluster aggregation, whereas at high molarities D agreed well with expectation for the diffusion-limited case. The cluster anisotropy was greater in the former regime than in the latter, again in accord with theoretical expectation. The change from one regime to the other occurred over a rather narrow range of electrolyte concentration.