Latex surface and bulk coagulation induced by solvent vapors

Latex exposure to solvent vapors leads to highly specific changes in latex stability as well as on the morphologies of the particle association produc ts, depending on the latex and solvent used. Examples of solvent vapor-indu ced aggregation are given: surface films are obtained on two PS latexes; in one case, the film surface is mirror-reflective and very hat, as evidenced by AFM. Another PS latex coagulates under exposure to acetone vapors, and the morphologies of the coagula are highly sensitive to the exposure condit ions. This latex yields a highly porous foam-like structure, in which parti cles are strongly coalesced but form percolating patches around the pores. The same latex but under other conditions produces a coagulum of large numb ers of aggregated particles with a raspberry-like morphology. Density centr ifugation experiments show that the effect of solvents on different latex f ractions is not uniform, and some fractions show larger density changes tha n others, thus evidencing a variability in their swelling ability. (C) 2000 Academic Press.