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

The possibility of obtaining narrowly dispersed particles through controlle d aggregation of polymer latices has been investigated. Concentrated polyst yrene 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 invo lves the formation of a 3-D network with a gel-like structure, formation of small, compact aggregates (termed primary aggregates) through the mechanic al disruption of this network, and further aggregation of the primary aggre gates into larger structures, termed secondary aggregates. Experimental evi dence 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 agg regation of these latices were explained through calculations of the fundam ental forces involved in this process. The method under investigation has b een effective in obtaining 5-15 mum particles with a narrow size distributi on and a strong control on the average size.