In situ monitoring of sorption and drying of polymer films and coatings: self-referencing, nearly temperature-independent fluorescence sensors

Sorption and drying processes were monitored in situ in polymer films by a fluorescence rotor probe, 4-tricyanovinyl-[N-(2-hydroxyethyl)-N-ethyl]aniline (TC1), a solvatochromatic fluorescence probe, 4-(N,N-dimethylamino)-4′-nitrostilbene (DANS), and pyrene. Taking advantage of an intensity ratio to monitor sorption, these fluorescence probes were found to serve as self-referencing sensors of water sorption in polyvinylacetate, with DANS being the most sensitive followed by TC1 and pyrene. Additionally, the shapes of the emission spectra (and thus intensity ratios) for TC1 and DANS were independent of temperature over a range of reasonable expected use temperatures. Covalent attachment of these fluorescence dyes was shown to enable the determination of sorbate levels within particular layers of multilayer films or coatings. Finally, these probes were also shown to provide sensitivity to desorption or drying of both water and organic sorbates.