Conductive polymer composites as gas sensors with size-related molecular discrimination capability

To prepare a novel gas sensor with selective sensitivity, waterborne β-cyclodextrin-block-polydiethylene glycol hexandioic ester copolymer was synthesized and blended with carbon black (CB). It was found that electric resistance of the composites remarkably increased upon exposure to vapors of low permittivity (like chloroform and tetrahydrofuran), while nearly no response can be detected to vapors of high permittivity (like water and methanol). What is more interesting is that the composite maximum responsivity was correlated to the molecular size of vapors of low permittivity on a half-logarithmic scale. With increasing the molecular size of the low permittivity gaseous analytes, the composite responsiveness gradually decreases. On the basis of this feature, molecular discrimination can be easily conducted. Mechanism study indicated that β-cyclodextrin rather than polydiethylene glycol hexandioic ester in the matrix polymer played the leading role in this aspect, which was explained from the viewpoint of host–guest chemistry and the hydrophobicity of the β-cyclodextrin cavities as well.