Continuously responsive epoxy-amine cross-linked silicon sol–gel materials

Advanced materials capable of responding to their chemical environment have been synthesized from the highly tailorable combination of sol–gel chemistry and epoxy-amine cross-linking reactions. Several materials were prepared from tetramethoxysilane (TMOS), and 3-glycidoxypropyltrimethoxysilane (GPTMS), and polyamine cross-linking agents. These cross-linking agents included diethylenetriamine (DETA), N-(2-aminoethyl)-piperazine (AEPZ), 1-(2-aminoethyl)- piperidine (AEPD), and ethylenediamine (EDA). Selective release of the indicator 4-methylaminoazobezene- 4¢-sufonic acid from these materials was monitored using UV–visible spectroscopy. Studies of the release demonstrate that it is continuously pH responsive with the greatest release at extreme pHs. Release is triggered by changes in the electrostatic interactions between the molecular additive and the matrix. These interactions can be readily tuned by altering the cross-linking agent