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Heterocoagulation behavior in concentrated mixtures of two rubbery latices of poly(styrene-co-butadiene) (SBR) and poly(butyl acrylate) (PBA) was studied as a function of the weight fraction of SBR φSBR. The latices are polymerized by an emulsion polymerization and they are similar in size, shape, and surface charge. Heterocoagulation was induced by the reduction of pH and its process was investigated in terms of the particle size distribution and the internal morphology of aggregates. The resulting aggregates consist of not only the primary particles of SBR but also composite aggregates including SBR and PBA. Their size, volume fraction, and morphology depend on φSBR. Formation of the intermediate aggregates with a core (SBR) – shell (PBA) morphology was confirmed by transmission electron microscopy (TEM). An aggregation mechanism consisting of the following successive two steps was proposed: step I, the formation of core–shell intermediates by preferential aggregation between the different primary particles and step II, further growth of the aggregates by a mutual aggregation between the intermediates. |
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