Triggered release of molecular additives from epoxy-amine sol-gel coatings

Two coatings capable of responding to their chemical environment have been synthesized using a combination of sol-gel techniques and epoxy-amine cross-linking reactions. These triggered release materials were prepared from tetramethoxysilane (TMOS), 3-glycidoxypropyltrimethoxysilane (GPTMS), methyltrimethoxysilane (MTMOS) and cross-linked with diethylenetriamine (DETA). Studies of the release of a molecular additive were performed in solutions ranging in pH from 2.5 to 11.0, over a 90-min period. The coating response is shown to be pH dependent with the greatest release occurring at the extreme pHs. Zeta potential measurements of the 1:3 coating were used to approximate the isoelectric point of the coating. Extreme-moderate pH cycling experiments were performed to determine the effect of matrix decomposition on the release of molecular additive from each of the coatings. These experiments indicate that electrostatic interactions and not coating decomposition is the major component of the release mechanism.