# Coagulation kinetics in concentrated dispersions

For a number of reasons, the traditional theories of coagulation kinetics are considered rather inappropriate in the case of highly concentrated dispersions. Therefore, there is a need to overcome the limitations in these existing theories so that a theoretical framework evolves for predicting the dynamics of coagulation in concentrated dispersions. Addressing this problem is not trivial because of the complexities related with the estimation of particle diffusivity in concentrated dispersions and the multiparticle interactions that control their colloidal stability. To complicate the matter further, the experimental measurement of coagulation kinetics is also a difficult task due to instrumental limitations In view of the above, an attempt is made in the study presented in this dissertation to develop a theory for predicting the dynamics of coagulation in concentrated dispersions. Alongside, efforts are undertaken to design an experimental procedure for measuring the same. The theory proposed in this research employs basic principles of statistical mechanics and the kinetic theory of gases. It also incorporates certain geometrical models for estimating the energies of multiparticle colloidal interactions that are pertinent for concentrated dispersions and which govern their coagulation behavior. The specific interactions considered are the electrical double layer and the van der Waals interactions The experimental procedure employs dynamic light scattering for measuring coagulation rates in concentrated dispersions. Coagulation is initiated in a concentrated polystyrene latex suspension by adding an electrolyte to it. Coagulation rate, the rate of decrease of total particle count with time, is then monitored by measuring the transient change in particle size distribution The experimental coagulation rates are then compared with the predicted values, thereby enabling verification of the validity of the developed theory. In such comparison, Hamaker constant is used as the fitting parameter. The value of Hamaker constant required in this theory to match the experimental results is an order of magnitude greater than the maximum value reported in literature. The use of the latter Hamaker constant value, however, leads to complete disagreement between the theory and the experiments