Absorption and diffusion measurements of water in acrylic paint films by single-sided NMR

Artists’ acrylic paint surfaces can accumulate surface grime. Aqueous surface cleaning of these paints can be particularly problematic because they swell upon exposure to water and because of the presence of water extractable additives. Research to determine the parameters of water penetration and swelling as well as the role of the water soluble additives in these phenomena is important in order to understand the leaching mechanism and possibly describe the best conditions for removal of water soluble grime. In this work, the penetration and molecular dynamics of water with different salt concentrations in films of artists’ waterborne acrylic paint were studied for the first time in situ using noninvasive single-sided nuclear magnetic resonance (NMR). This novel approach demonstrated that the absorption of water in the acrylic film is independent of the salt concentration, whereas the absorption of water in water-washed acrylic paints, after the water soluble components have been removed, is not only 15% less than unwashed paint films but it also decreases with increasing salt concentration. In addition, the self-diffusion coefficients of water within the acrylic polymeric network were determined and analyzed. The diffusion coefficients of water depend only slightly on the salt concentration and are only marginally influenced by the amount of incorporated surfactants. Thus the diffusion rate of water within the acrylic polymer film appears to be almost independent of the salt concentration or the surfactant content.