A Study of Colloidal Particle Brownian Aggregation by Light Scattering Techniques

Aggregation kinetics and aggregate structure are studied for monodisperse polystyrene latex particles of diameter 60 and 140 nm. The experimental part consists of measurements over a rather broad range of electrolyte concentrations (0.1 to 0.8 M NaCl) and for particle volume fractions 10(-6) to 10(-5), using dynamic and static light scattering techniques. The aggregation kinetics data obtained can be fitted into a single curve with a proper scaling of time and size for both particle sizes. For relatively long times, we observe power-law type kinetics, characteristic of diffusion limited aggregation (DLA). Fractal dimensions in all cases are close to 1.7 (as expected for DLA). The light scattering behavior of aggregates of arbitrary size is also studied numerically by employing computer simulations, and existing models (Lin et al., 1990. J. Colloid Interface Sci. 137, 263) are tested and improved for certain conditions (large angles and/or large particles). The shape of the experimental kinetics curves is successfully described with numerical simulations, further suggesting that (under the conditions tested) DLA aggregation prevails for short times as well. Copyright 1997 Academic Press. Copyright 1997Academic Press