The production or handling of colloidal particles is relevant to a great deal of industrial areas, such as food, plastics, paints, coatings and paper treatment. A key feature of colloidal particles is their kinetic stability: the dispersed particle phase eventually phase-separates from the continuous one it is suspended into. This process is mediated by the formation of aggregates exhibiting a self-similar (i.e. fractal) nature, with fractal dimensions regulated by the conditions in which the destabilization occurs. For instance, open clusters are formed in fully destabilized systems where the cluster aggregation is diffusion limited (DLCA), whereas in reaction-limited cluster aggregation (RLCA) more compact clusters are formed, as not every aggregation event is an effective one due to typically charge-induced particles stability. This picture changes when the aggregating particles are soft enough for coalescence to occur in a comparable timescale as aggregation. Indeed, coalescence leads to an interpenetration of the particles constituting a cluster, therefore compacting the cluster itself and increasing its fractal dimension. As a result, the aggregation rate is affected: compact clusters tend to aggregate slower than more open aggregates (of the same mass) and the probability of encountering and aggregating with another cluster is larger for an open cluster which presents a larger collision radius compared to a more compact aggregate. [1,2]
In this frame, the aim of the present work is to shed further light on the aggregation-coalescence process for polymer particles along the following lines: i) developing a computationally effective population balance equation (PBE) based model able to account for both aggregation and coalescence, ii) develop the necessary equations to relate the PBE results with light scattering quantities (e.g. the hydrodynamic and gyration radii) and, iii) compare the model predictions with experimental results. To this end, polymeric particles with different glass transition temperatures were prepared and their aggregation behavior was studied in stagnant DLCA conditions (at different temperatures and particles concentrations) by means of light scattering techniques. The obtained experimental results were then compared with the model predictions, requiring solely one fitting parameter, based on the coalescence characteristic time. Despite of its simplicity, the model predictions along with the newly derived light scattering correlations were able to well-describe the observed experimental data.
 Cosgrove, T., Colloid science principles, methods and applications. 2nd ed.; Wiley: Chichester, U.K., 2010
[2 ]Berg, J. C., An introduction to interfaces & colloids - the bridge to nanoscience. World Scientific: Hackensack, 2010