Pyridinium surfactants can modulate the UV response of methyl green dye-doped polymeric films for sensor development

Abstract

Concerns about ultraviolet radiation (UV-R) are increasing due to climate change. The effects of UV-R on living organisms depend on exposure duration and intensity, making it crucial to monitor UV-R levels. In this study, we investigated the role of surfactants as photosensitizing or stabilizing agents in a colorimetric sensor based on a polymeric film doped with methyl green dye. The films were synthesized using the casting technique from a filmogenic solution containing either carboxylated polyvinyl alcohol (P1) or hydroxylated polyvinyl alcohol (P2). We evaluated the impact of surfactant structure (dodecylpyridinium chloride, C12; hexadecylpyridinium chloride, C16; or sodium dodecyl sulfate, SDS) and concentration on the colorimetric response of the films to UV-R. Color changes were monitored using the CIELab system. The results showed that, under UV-R exposure for up to 5 h, films without surfactants did not lose their blue hue (negative b* parameter in CIELab). While SDS stabilized the dye in the polymeric matrix, films containing pyridinium surfactants (C12 or C16) changed color from blue to pale yellow (positive b* parameter in CIELab). The color change, which was modulated by surfactant concentration, was attributed to radical reactions involving the pyridinium surfactants, influenced by their hydrophobicity and the polymer structure. These results represent a significant advancement in colorimetric sensors for UV-R, as they allow for the modulation of the sensor's response time through surfactant concentration in the polymeric film.