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

A polystyrene (PS) latex prepared by redox initiation is coagulated by expo sure 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 alcoh ols and many other solvents. Latex particle size determinations by PCS, und er various exposure conditions, show that the vapor-induced coagulation tak es place at the liquid latex surface, rather than within the liquid, but th e 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 S EM examination of dry coaguli formed under ethanol vapor. (C) 2000 Elsevier Science B.V. All rights reserved.