Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE ABSTRACT
Building on a quartz crystal microbalance with dissipation monitoring (QCM-D), fouling in emulsion polymerization was compared between acrylate dispersions stabilized with a mobile, anionic surfactant and dispersions of poly(vinyl acetate-co-vinyl neodecanoate), PVAc, stabilized with polyvinyl alcohol, PVOH. The PVOH chains covalently graft themselves to the PVAc chains as the reaction proceeds. Polyacrylate dispersions induce compact fouling layers with a thickness of a few particle diameters, while PVAc dispersions induce soft, extended layers. Those differences become evident in QCM experiments in the form of the ratio between the shift in half-bandwidth, ΔΓ, and the negative frequency shift, −Δf. Compact layers lead to ΔΓ/(−Δf) ≪ 1, while semi-infinite samples lead to ΔΓ/(−Δf)≈1. Presumably, polyacrylate particles coalesce to form a film. Surfactant is exuded to the top and creates a charged surface, which repels newly arriving particles. This mechanism limits the thickness of the layer. PVAc particles cannot merge and compactify in the same way because the emulsifier is covalently attached and can therefore not be displaced from the surface. Also, vinyl acetate is rather well soluble in the water phase, which allows for chemical reactions stabilizing the open and porous structure.