Probing the Cleaning of Polymeric Coatings by Nanostructured Fluids: A QCM-D Study

Complex fluids composed of water, an organic solvent, and a surfactant have been recently employed as cleaning systems to remove hydrophobic materials, such as polymeric coatings, from solid surfaces. The simultaneous presence of surfactants and an organic solvent with good affinity for the polymer was proven necessary for the polymer's removal, but the comprehension of the cleaning mechanism is poorly understood. In this Article, we investigated the mechanism of removal, highlighting the specific role of each component in the interaction with the polymer film. In particular, the results from quartz crystal microbalance with dissipation monitoring (QCM-D) were compared with those obtained by using confocal microscopy to follow in situ the effect of a nanostructured fluid, i.e., a ternary formulation containing water, 2-butanone (MEK) as a good solvent for the polymer, and a nonionic surfactant (C_9-11 ethoxylated alcohol, BR) on acrylic copolymer films (Paraloid B72). The results indicate a two-step process: (i) the penetration of the good solvent across the film causes the swelling of the polymer, the weakening of polymer-polymer interactions, and an increase of molecular mobility, followed by (ii) the slow adsorption of amphiphilic aggregates promoting the film detachment from the solid substrate. A different behavior is observed in the presence of similar formulations containing an anionic surfactant (sodium dodecyl sulfate, SDS), where the adsorption of SDS micelles on the surface of the polymeric film hinders solvent access into the polymer layer, rather than promoting its detachment from the solid substrate.