Controlled aggregation of polymer latices part 2. Mechanism and hydrodynamics of the process

The possibility of obtaining narrowly dispersed particles through controlled aggregation of polymer latices has been investigated. Concentrated polystyrene and poly(styrene-co-acrylic acid) latices were aggregated through the addition of tetradecyl trimethyl ammonium bromide under stirring. A three-step mechanism for the aggregation process is proposed. This mechanism involves the formation of a 3-D network with a gel-like structure, formation of small, compact aggregates (termed primary aggregates) through the mechanical disruption of this network, and further aggregation of the primary aggregates into larger structures, termed secondary aggregates. Experimental evidence in support of this mechanism is presented. The influence of stirring rate on the size and size distribution of secondary aggregates is discussed in conjunction with the mechanism proposed. The trends observed in the aggregation of these latices were explained through calculations of the fundamental forces involved in this process. The method under investigation has been effective in obtaining 5-15 mum particles with a narrow size distribution and a strong control on the average size.