Organic vapor sensing behaviors of conductive thermoplastic polyurethane–graphene nanocomposites
Conductive thermoplastic polyurethane (TPU) nanocomposites filled with graphene were fabricated and tested for organic vapor sensing. The observed finely dispersed graphene in the TPU matrix benefited from the formation of efficient conductive paths and the generation of stable electrical signals. Organic vapor sensing behaviors of the conductive polymer composites (CPCs) were evaluated using four kinds of organic vapors possessing different polarities (p), including cyclohexane (p = 0.1), tetrachloromethane (CCl4, p = 1.6), ethylacetate (p = 4.3) and acetone (p = 5.4). Unlike conventional CPCs that only respond to certain specific groups of organic vapors, the current CPCs showed a novel negative vapor coefficient (NVC) effect for all tested vapors. This observed NVC was due to both the inherent microphase segregation structure of TPU containing soft and hard segments and the wrinkled structure of graphene. In successive immersion-drying runs (IDRs) at 30 °C, fast response, good reversibility and reproducibility were observed for the non- and low- polar vapors (cyclohexane and CCl4), but residual resistance was observed for polar organic vapors (ethylacetate and acetone) after their desorption. The temperature dependent vapor sensing behaviors indicated that the vapor sensing responsivity increased with increasing the temperature due to higher absorption activation energy at higher temperature. This study provides guidelines for the fabrication of organic vapor sensors using CPCs possessing fast response, good discrimination ability and reproducibility.