Redispersing aggregated latexes made with switchable surfactants

Amidine-based switchable surfactants can be used as stabilizers during emulsion polymerization, and the resulting latexes can then be destabilized simply by the removal of CO 2 . Polystyrene and poly(methyl methacrylate [MMA]) latexes have been successfully redispersed by reintroducing CO 2 to the latex, as shown by recovery of primary particle size, but an input of energy was required. Sonication is the most effective method of energy input, but lower-energy methods, such as rotor–stators and a blender, are successful in redispersing some aggregated latexes. Colloidal stability was found to be reversible for at least three aggregation/redispersion cycles, and redispersibility was achieved even after the removal of water and addition of fresh water. The traditional method of aggregating latexes involves addition of salts, acids or bases, which result in a contaminated wastewater stream. Furthermore, aggregated latexes cannot usually be redispersed. This approach could enable dewatering of latexes prior to transport followed by redispersion at the point of use, yielding significantly reduced transportation costs and energy consumption.