Latex coagulation induced by alcohol vapors: an unusual factor for colloidal instability

A polystyrene (PS) latex prepared by redox initiation is coagulated by exposure to the vapors of lower alcohols (methanol to 2-butanol) as well as to alcohol-water ( > 30% w/w) solutions, but not to the vapors of higher alcohols and many other solvents. Latex particle size determinations by PCS, under various exposure conditions, show that the vapor-induced coagulation takes place at the liquid latex surface, rather than within the liquid, but the effect of co-solvent alcohols on particle diameters under non-coagulating concentrations is significant (similar to 10%). Two major fractions of the latex are discerned by centrifugation in density gradients as well as by SEM examination of dry coaguli formed under ethanol vapor. (C) 2000 Elsevier Science B.V. All rights reserved.