Electrokinetic properties, colloidal stability and aggregation kinetics of polymer colloids

The purpose of this article is to present some important advances in the electrokinetic and colloidal characterization of polymer colloids. Special attention is paid to the new electrokinetic techniques: diffusiophoresis, dielectric dispersion and electro-acoustic. Also the most recent theoretical approaches are reviewed with respect to the electrokinetic properties of polymer colloids. Recently there has been intense discussion concerning electrokinetic processes and the theories used for data interpretation. Several concerns have been raised relating to the inability of the different processes and theories to yield the same electrokinetic potential. The most important explanations (shear plane expansion, preferential ion adsorption, osmotic swelling, crossing of the mobility/zeta-potential and anomalous surface conductance) to the electrokinetic behaviour of polymer colloids are discussed and analyzed. Also the effect of heat treatment on the electrokinetic properties of different types of polymer colloids is extensively considered. With regard to the colloidal stability of polymer colloids, three- and two-dimensional aggregations are presented. First, the stability factor W is introduced using the classical theory DLVO and the values obtained of Hamaker constant compared with the theoretical values estimated from the Lifshitz theory. The differences usually found by several authors are explained as due to the hydrodynamic interaction. Special attention is paid to the extended DLVO theory for studying homocoagulation of polymer colloids in three dimensions and to the new expressions for the van der Waals, electrostatic and structural forces that must be deduced to study the colloidal stability of polymer colloids in two dimensions. Also, the heterocoagulation of polymer colloids with different sign of surface charge density and particle size is reviewed, and a new definition of the heterocoagulation stability factor is given. The aggregation kinetics of polymer colloids in three dimensions is analyzed using the Smoluchowski theory (in terms of the reaction kernels k(ij)) in the cases where the Smoluchowski's equation is analytically solvable (constant, sum, product kernel and linear combinations thereof). The dynamic scaling in aggregation phenomena with polymer colloids is studied using the classification scheme for homogeneous kernels due to Van Dongen and Ernst based on the relative probabilities of large clusters sticking to large clusters, and small clusters sticking to large clusters. The techniques (multiparticle and single particle detection) enabling us to provide cluster-size distribution of aggregating polymer colloids are also presented. Finally, the aggregation kinetics of two dimensional aggregation of polymer colloids is studied on the basis of the fractal dimension of the aggregates. The different scaling theories for two-dimensional aggregation are also considered.