SURFACTANT EXUDATION IN THE PRESENCE OF A COALESCING AID IN LATEX FILMS STUDIED BY ATOMIC-FORCE MICROSCOPY

We report atomic force microscopy images of surfactant (SDS) exudation in PBMA latex films, in the presence and the absence of a coalescing aid (TexanolTM, TPM). The exudates appear as hilly islets, and at time s as mountains, at the film surface. Their size and number increase up on annealing above the glass-transition temperature of the latex polym er. TPM was found to be a strong promoter of surfactant exudation at t he air-polymer interface. In the absence of TPM, annealing the films f or several hours at 70 degrees C led to very little migration of surfa ctant to the surface at most sites in the film. When the films with st ructures of SDS on their surface were immersed in water, these structu res disappeared. Pores, ranging in size from tens to hundreds of nm in diameter, were clearly visible in the surface of the films. These fil ms dry from the edges of the film inward, with a propagation front con centrating the water-soluble species into a turbid, moist region in th e center. At this site, the rate at which the surfactant comes to the surface is enormously enhanced over that at other sites in the film. T his is likely due to the high concentration of surfactant in this regi on, transported there by the drying process. (C) 1995 John Wiley & Son s, Inc.