Sensor properties of SBS block copolymer and carbon composite film structures

Abstract

Carbon composite thin films were prepared from a styrene butadiene styrene (SBS) block copolymer matrix with dispersed graphitic carbon as the second phase. Precursor solutions in the viscosity range of 150–200 cps were developed from codispersion of SBS–carbon in toluene as solvent base. Film coatings were prepared by spin coat onto glass, alumina or silicon substrates at 2000 rev min−1 followed by drying and vacuum heat treatment at ∼80°C. Characterisation of the films was carried out using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and SEM techniques. Degree of crystallinity in the composite film structures was correlated with the strong positive temperature coefficient (PTC) effect. These composite thin films also showed high resistance sensitivity to temperature in the range from 2 90 to −90 to +90°C. A unique feature of the resistance/temperature response was the observed negative temperature coefficient (NTC) behaviour below ∼0°C combined with a strong PTC response above ∼0°C. When exposed to various organic vapours, the composite films showed high selectivity, indicated by sensitive change in resistivity values.