Sensors for liquids based on conductive immiscible polymer blends

The present paper discusses the application of conductive immiscible polymer blends as sensor materials for detection of organic liquid solvents and of their vapors. Immiscible polymer blends of high impact polystyrene (HIPS), ethylene vinyl acetate copolymer (EVA) and carbon black (CB), and compounds of EVA/CB have been used to produce a series of electrically conductive filaments by a capillary rheometer process. In these immiscible blends, HIPS serves as a matrix and EVA as the semi-crystalline dispersed phase. The enhancement of conductivity in these blends is due to the attraction of CB to EVA, giving rise to conductive networks. The de electrical resistivity of extruded filaments, produced at different shear levels, is found to be sensitive to various organic liquid solvents. The shear rate, at which the filaments are produced, has an important effect on the HIPS/EVA/CB filament's sensitivity. The compositions studied were close to the double-percolation structure believed to perform best as sensor materials. The HIPS/EVA interface seems to play an important role in the sensing process. In some cases, liquid contact/drying cycling of filaments indicates stabilization of the sensitivity change, making the sensing process reversible. Liquid transport principles are an important basis for interpretation of the sensing behavior of immiscible blend-based filaments in contact with liquids. (C) 2000 Published by Elsevier Science S.A. All rights reserved.