Electrical and humidity sensing properties of carbon nanotubes-SiO2-poly(2-acrylamido-2-methylpropane sulfonate) composite material

Alkali salts of poly(2-acrylamido-2-methylpropane sulfonate) (PAMPS)-SiO2 and single-walled carbon nanotubes (SWCNTs)-SiO2-PAMPS were used as composite materials to make a humidity sensor. The impedances of these composite materials were measured at various humidities and temperatures in the frequency range of 1–100 kHz. The results indicated that the H+ form of the PAMPS-SiO2 composite film had the highest electrical conductance. For practical use, a humidity sensor, which was a low-resistance device, commonly required for electronic circuit compatibility, was prepared from SWCNTs-SiO2-PAMPS composites. The sensing mechanism of the SWCNTs-SiO2-PAMPS composite films were explained by considering the observed impedance plot and activation energy compared with a SiO2-PAMPS composite film. At low relative humidity (RH), new conductive paths were formed, whereas with increasing RH, the ionic contribution became prevalent. Other sensing properties of the SWCNTs-SiO2-PAMPS composite films such as effects of applied frequency, ambient temperature and hysteresis were also investigated.