ON THE MODEL OF COLLOID AGGREGATES AND AGGREGATING COLLOIDS

Computer simulations were used to investigate the power law dependence of the elastic compression modulus and the yield stress (is proportional to R(-gamma)) of two-dimensional (2D) and three-dimensional (3D) aggregates of special type (fractal trees without loops on square and simple cubic lattices) on the radius R of the aggregates. The elastic forces between particles were described by the Born model. Scaling exponent-gamma was found to be slightly dependent on the geometrical parameters of the aggregates internal structure and the parameters of interaction (it ranges in the limits 1.3-1.7 in 2D and 1.8-2.6 in 3D). If the interparticle forces are purely central, the internal structure of aggregates is not able to transmit any elastic stress. In this case simulations of the disaggregation process were carried out in 2D in free draining approximation. It was shown that the initial aggregate is broken into two or more secondary aggregates. The mean radius of these aggregates decreases as the shear rate increases. Relevance of these data for the microrheological models of aggregating colloids in shear flow is demonstrated. In terms of the mean field model, the viscosity of aggregating colloid is calculated as a function of shear rate. In this model aggregates are characterized by two exponents: fractal dimension and gamma. The values of gamma, which were obtained in our simulations, are found to be close to those values which are needed to find the best fit between the mean field model and the computer simulations data for aggregating colloids previously obtained by other authors.