Fractal aggregation of polystyrene spheres in the crossover region between DLCA and RLCA

Abstract

We investigate both kinetics and fractal morphology of aggregating polystyrene latex, by means of a low-angle static light-scattering setup, covering two decades in scattering wavevectors. — The reactions are induced by adding various salt concentrations ranging from a value typical of diffusion limited colloid aggregation (DLCA) to one close to reaction limited colloid aggregation (RLCA). — The data show that the time evolution of the weight average molecular weight of the clusters is power law, with an exponent z varying in a continous fashion with the salt concentration c. — Measurements of the fractal dimension d _f are performed for each run. At high c (DLCA) the results are in good agreement with previous works: d _f is stable in time and equal to 1.65. For lower concentrations, however, d _f gradually decreases in time from 2, a value typical of RLCA, to lower values, close to the DLCA one. It should be pointed out that decreasing the salt concentration d _f becomes higher and more stable in time. — The data are interpreted consistently with both theoretical and simulation works presently available.