CHEMICALLY ACTUATED ELECTRONIC SWITCH

A new liquid phase chemical sensor is described based on the swelling of an electrically conductive polymer composite, where the polymer matrix serves as the chemical sensing element, and a conductive filler is used solely to achieve film volume resistivities, ρ, of less than c. 10 ohm cm in an unswollen state. In the presence of a solvent with a large solvent-polymer interaction coefficient the polymer swells to such an extent that electrical conduction is highly impeded, i.e. ρ > 109 ohm cm, by the increased separation between conducting microstructures. A typical system is demonstrated for the detection of low molecular weight hydrocarbons using a carbon black/silicone elastomer composite. For such systems the swelling is reversible upon elimination of solvent; and, switching times < 1 s are commonly observed for a thin-film sensor. The response is also discussed for two component mixtures comprised of swelling and non-swelling agents. © 1990.