0-3 composites consisting of carbon black and vanadium oxide conductive fillers in polyethylene, a polyurethane, and polyvinyl alcohol have been developed for use as chemical sensors. Polymer matrices loaded with conductive filler near the percolation threshold swell reversibly in the presence of liquid and gaseous solvents, disrupting the conductive pathways and proportionally increasing the resistance. The magnitude of the swelling (which usually dominates the magnitude of ΔR) depends on the solubility of a given solvent in the polymer. For non-polar materials, the swelling can be predicted by considering the difference in solubility parameters of polymer and solvent, although the overall magnitude of ΔR may also be influenced by particle morphology, the percolation behavior for the system of interest, and other undefined solvent/polymer/filler interactions. The response time of the sensor is determined primarily by the sample thickness and the diffusion of the solvent through the polymer. Response times will play a role in determining the selection of a sensor for a particular application.
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