| abstract |
The present invention provides a gel-matrix whose electrical and/or thermal conductivity undergoes a significant change in response to minor variations in one of several externally controlled thermodynamic parameters, such as temperature, pH, ionic strength, and solvent composition. The matrix is formed by at least three primary components: conductive particles, swellable and deswellable crosslinked particles, and a solvent system. In the de-swollen state, the gel particles occupy a relatively small volume fraction of the gel-matrix, allowing the conductive particles to be discrete, fully suspended, and free flowing in the solvent system. Upon switching to the swollen state, the interstitial volume between the crosslinked gel particles diminishes, forcing the conductive particles to come into intimate contact with one another, thus creating a conductive percolation network. As a result, the electrical and/or thermal conductivity of the matrix is increased appreciably, because the interparticle connectivity among the conductive particles governs the electrical and/or thermal conductivity of the composite article. The conductivities exceed prior formulations with similar rheological characteristics, making such composite articles ideal for a number of specialized applications. Temperature-, pH-, ionic-strength-, and solvent-composition-sensitive switchable media are therefore prepared. |