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 (∼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.