A PRELIMINARY FTIR-BASED EXPLORATION OF THE SURFACTANT PHASE SEPARATION PROCESS IN CONTEMPORARY MURAL PAINTINGS

This paper reports on a preliminary evaluation of a degradation process that may affect mural paintings created with emulsion products: the phase separation of paint additives towards film-environment and film-support interfaces. A number of mock-ups were prepared by brushing five acrylic, five vinyl and five styrene-acrylic paints on cement-lime mortar supports. A selection of these samples was stored under laboratory conditions to verify the appearance of exudation phenomena, and to compare the stability of paints having different chemical composition. Since water was suspected to influence the phase separation process, the remaining samples were deteriorated simulating the absorption of water into the mortar supports by capillary rise mechanism. This degradation process forced the paint layers to delaminate from the supports, allowing the exploration of the two interfaces (the one in contact with mortar and the one exposed to the environment) by mid-near FTIR reflection spectroscopy. According to the results, capillary rise seemed to promote surface exudation of non-ionic polyethoxylate type surfactants, but the process was also influenced by the chemical composition and the properties of the paint layers. No water-soluble paint components were detected at the film-support interface.