Mobility and distribution of silicone additives in coatings; a spectroscopic study

The concentration of four prepared silicone/poly(ether) additives at the film-air (F-A) and film-substrate (F-S) interfaces of films prepared on glass and poly(ethylene) substrates is characterized via quantitative attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy. Three different coating systems, an acrylic/melamine solvent based system, an acrylic/isocyanate solvent based system, and an aqueous poly(urethane) suspension, were examined. It is found that the nature of the substrate, the mechanism of film formation, and the inherent coating/additive compatibility are all factors which may significantly influence additive behavior. Also the acrylic/melamine system generally reveals a slight degree of enrichment of both additive components to the F-A interface, but the acrylic/isocyanate system exhibits a more pronounced concentration gradient due to a lesser degree of compatibility. In contrast, the water-based poly(urethane) exhibits a more complex behavior, with the poly(ether) component revealing significant enrichment to the F-A interface, and the siloxane component exhibiting a decreased concentration as the interface is approached. Here, the mechanism of film formation involves a water flux passing out of the film which may serve to transport the water soluble poly(ether) components to the F-A interface. At the F-S interface, it is demonstrated that the nature of the substrate may influence additive behavior, and it is found that the concentration of the more polar poly(ether) components generally exhibits a lesser degree of enrichment to a poly(ethylene) substrate, relative to glass.