A STUDY OF COLLOIDAL PARTICLE BROWNIAN AGGREGATION BY LIGHT-SCATTERING TECHNIQUES

Aggregation kinetics and aggregate structure are studied for monodispe rse polystyrene latex particles of diameter 60 and 140 nm. The experim ental part consists of measurements over a rather broad range of elect rolyte concentrations (0.1 to 0.8 M NaCl) and for particle volume frac tions 10(-6) to 10(-5), using dynamic and static light scattering tech niques. The aggregation kinetics data obtained can be fitted into a si ngle curve with a proper scaling of time and size for both particle si zes. For relatively long times, we observe power-law type kinetics, ch aracteristic of diffusion limited aggregation (DLA). Fractal dimension s in all cases are close to 1.7 (as expected for DLA). The light scatt ering behavior of aggregates of arbitrary size is also studied numeric ally by employing computer simulations, and existing models (Lin et at , 1990. J. Colloid Interface Sci. 137, 263) are tested and improved fo r certain conditions (large angles and/or large particles). The shape of the experimental kinetics curves is successfully described with num erical simulations, further suggesting that (under the conditions test ed) DLA aggregation prevails for short times as well. (C) 1997 Academi c Press.