Abstract
Special, unexpected properties may arise from blending of polymer emulsions, depending on the miscibility and stability of the resulting dispersions on the one hand, and the morphology of the films obtained upon drying on the other hand. In the field of water‐repellent paints, blends of silicone and vinylacrylic copolymer emulsions have been previously shown to be a tricky means to associate binding ability and water permeability properties in the same material. It is currently assumed that the resulting morphology and physical properties of films obtained from these blends upon drying is partially controlled by the compatibility of the two kinds of polymers. In the present paper, the crucial problem of stability and compatibility in blends of silicone and vinylacrylic copolymer emulsions is investigated; more particularly, the effect of pH of the vinylacrylic copolymer latex, as well as the influence of the stabilizing system of both emulsions, on the stability of emulsion blends is qualitatively described. As regards the morphology of the films, the strong incompatibility of the two polymers is shown, which results in large macroscopic heterogeneities in the dried composite films. Furthermore, semi‐quantitative angle‐resolved ESCA measurements have evidenced a pronounced diffusion of the silicone species towards the surface of the samples. Investigations into different ways to increase compatibility of the two phases is presented. It is shown that phase separation at the macroscopic scale can be controlled either by lowering the interfacial tension between the two phases by grafting silane compatibilizers on to the latex particles, or by decreasing the molecular mobility of the silicone phase by cross‐linking. Diffusion of the silicone chains towards the surface of the composite films can only be significantly restricted by cross‐linking of this species.