Assessment of the Aggregation Dynamics of Latex Particles

Original experimental and modeling methods are proposed to evaluate the colloidal stability of latex particles. The first experimental method employs a rheometer operating under controlled shear rates in a laminar regime to induce particle aggregation. This approach is suitable for concentrated latex samples, however the change in the particle size distribution (PSD) is measured offline. The second method uses a laser diffraction granulometer, which introduces higher shear forces due to mixing and pumping. In this case, changes in PSD are measured in real time, but the latex must be diluted. In both methods, the observed coagulation mechanism consists of a very small fraction of the latex particles aggregating directly into very large clusters, with a progressive increase in the aggregation fraction (not size) with time. This behavior contrasts with common aggregation models, where usually binary aggregation is assumed, and is applied to all particles. While the observed mechanism in these devices may differ from that occurring in a reactor, both methods proved useful for qualitatively assessing the aggregation dynamics of the latex, thus informing on its stability. A simplified model was then developed to quantify the latex stability under various conditions. This approach helps evaluate the shear levels (rate and duration) that induce particle coagulation, thus offering useful information for reaction design and product formulation.