Heteroaggregation in colloidal dispersions

The theory of heteroaggregation is an important concept for the understanding of many natural and industrial processes. It relates to any process where particles differ. It is based on an expansion of the DLVO theory, and now involves highly mathematical computation. Heteroaggregation has been continually developed to extend the use of a formula to encapsulate all particle type variations. McCormack et al. [29] have reported such an equation, and it is necessary for these complex equations to be related to experimental conditions. f the early forms of the theory of heteroaggregation were based on the use of assumptions such as constant surface potential, constant surface charge conditions and that surfaces are smooth. This is now known to cause anomalies in the theoretical predictions when compared to the experimental situation, as the situation of a discrete surface charge is more applicable for colloidal particles due to the heterogeneous nature of the surface [41]. Furthermore, particle surfaces are rarely smooth. Another problem highlighted is that the theoretical predictions are influenced by particle size, and yet when assessed experimentally no such dependence was recognised [58]. This inconsistency is attributed to the inability of the DLVO theory to consider the dynamics of particle-particle interactions. eview has focused on aqueous systems, although work has been reported in non-aqueous environments, for example toluene, in which the heteroflocculation of non-aqueous silica dispersions were investigated by Skuse et al. [85]. In this example, adsorption was controlled by strong Lewis acid-base interactions. Deflocculation was achieved by the addition of strong acid or base, which is in contrast to aqueous systems where high concentrations of electrolytes are used to induce desorption. eview also defines both Brownian and shear coagulation mechanisms, although most of the theories stated relate to Brownian coagulation. Shear coagulation introduces new mathematical equations and system parameters. Wang [2] and Adler [73] have reported in-depth studies in this field. aggregation in colloidal particles is therefore, an important concept for both a fundamental and for an applied understanding in colloidal science which, from a theoretical point of view, is still in its infancy when considering the sophistication and accuracy of the models developed to describe experimentally observed behaviour. A challenge, therefore, exists to advance this field in an attempt to gain a clearer picture of the often complex interactions which exist between unlike particles.