Morphological Changes in Latex Films

Abstract

Abstract The mechanism of latex particle coalescence has been considered by a number of investigators. Dillon and coworkers and later Henson and coworkers discussed the role of surface tension forces and the applicability of Frenkel's model for coalescence of spheres by viscous flow. Later Brown postulated that capillary forces derived from the water and air interfacial tension, when the evaporation of the water forms small radii of curvature, provide the major driving force for film formation. Voyutskii stated that the surface tension and capillary forces alone cannot account for the ultimate physical properties observed in cast latex films. He postulated the contribution of autohesion, that is, mutual interdiffusion of the free polymer chain ends across the particle, particle interface in the dried film. According to his hypothesis, this diffusion knits the film into one coherent, continuous mass. It has often been observed that physical properties of latex films improve with aging at room conditions. This improvement occurs after practically all the water has evaporated and the films are transparent. Thus, the empirical observations of such properties as scrub resistance indicate that the dry latex films undergo some change upon aging. The autohesion hypothesis might explain these results. In this study the electron microscope was used to study morphological changes which occur as a latex film ages. The magnification of this instrument allows the observation of individual particles in the film surface and the changes with aging.