The aggregation of dense colloidal solutions has been investigated by means of low-angle static light scattering. We show that the scattered pattern exhibits a finite-^-vector peak, whose intensity and position q m change with time. We find that the intensity distributions scale according to S(q/q m ,t) -q m (t) ~dF(q/q m )y in agreement with the scaling law for spinodal decomposition. While

No abstract

We show that the two point intensity correlation in the near field of the scattered light is directly related to the two point density correlation g(r). Preliminary measurements on two sets of calibrated random pinholes of 140 and 300 &mgr;m diameters, and on aqueous solutions of latex spheres of 5, 10, and 40 &mgr;m are reported. A discussion on the desirability of the technique as a simple and powerful alternative to low angle scattering will be presented.

We investigate the kinetics and fractal morphology of aggregating polystyrene latex in an intermediate region between diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation (RLCA). The measurements are made by means of a low-angle elastic-light-scattering setup covering two decades in scattering wave vectors. For each aggregation run, the salt concentration c is changed and the samples are prepared under isopycnic conditions, to avoid differential sedimentation. The average cluster mass is found to grow according to a power law with an exponent z varying in a continuous fashion in the range of salt concentration used. At high c (DLCA), we find for the fractal morphology df =1.65. For lower concentrations, df is at first larger than 2 and therefore close to the typical RLCA fractal dimension, but then it gradually reverts to lower values not far from those typical of DLCA. This behavior is also exhibited at the lowest values of c explored, although the decay to DLCA is much slower. An interpretation of the results is presented on the basis of the available theories and simulation work on the cluster morphology in the intermediate regimes.

No abstract