RESUMO
Poly(styrene-co-acrylamide) (PS-AAM) latex was prepared, fractionated by sedimentation under gravity, and characterized by PCS, infrared spectra, secondary and backscattered electron imaging in the scanning electron microscope, and electron spectroscopy imaging in an analytical transmission electron microscope. Three latex fractions were obtained. The lower fraction was opalescent and its particles were the more uniform, concerning size, chemical composition, and topochemical features. This lower fraction was still further fractionated by zonal centrifugation in a density gradient, yielding two fractions with similar macrocrystal-forming abilities but different sizes and chemical compositions. These results confirm those previously obtained for the PS-HEMA latex. Copyright 2000 Academic Press.
RESUMO
Latex exposure to solvent vapors leads to highly specific changes in latex stability as well as on the morphologies of the particle association products, depending on the latex and solvent used. Examples of solvent vapor-induced aggregation are given: surface films are obtained on two PS latexes; in one case, the film surface is mirror-reflective and very flat, 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 conditions. This latex yields a highly porous foam-like structure, in which particles are strongly coalesced but form percolating patches around the pores. The same latex but under other conditions produces a coagulum of large numbers of aggregated particles with a raspberry-like morphology. Density centrifugation experiments show that the effect of solvents on different latex fractions is not uniform, and some fractions show larger density changes than others, thus evidencing a variability in their swelling ability. Copyright 2000 Academic Press.
