Stimuli-responsive epoxy coatings.

The design, formulation, and characterization of new epoxy coatings with built-in chemical and threshold temperature sensors are reported. The materials were prepared by dissolving a chromogenic, fluorescent oligo(p-phenylenevinylene) dye into a cross-linked epoxy resin by reacting monomer/cross-linker/dye mixtures at 180-200 degrees C and quenching the cured polymer to below its glass transition temperature (T(g)). Subjecting these kinetically trapped, thermodynamically unstable molecularly mixed epoxy/dye blends to temperatures above T(g) leads to aggregation of the dye molecules and causes permanent and pronounced changes of their optical absorption and fluorescence properties. Exposure of the materials to selected chemical stimuli, e.g., water, acid, base, and several organic compounds, also causes plasticization of the polymer matrix and leads to irreversible aggregation of dye molecules, concomitant with the pronounced fluorescence and absorption color change. This response is well described by standard kinetic models and can be controlled via the chemical structure and cross-link density of the resin and the dye content.