In situ synthesized composite thin films of MWCNTs/PMMA doped with KOH as a resistive humidity sensor

In situ synthesized multi-walled carbon nanotubes (MWCNTs), methyl methacrylate (MMA) and KOH composite thin films on an alumina substrate were used to fabricate resistive humidity sensors. The thin films were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and Fourier transform infrared spectroscopy (FT-IR). The electrical characteristics of PMMA to which various amounts of MWCNTs were added were measured in detail as a function of relative humidity (RH), to elucidate the contribution of MWCNTs to the humidity-sensing capacity. The humidity-sensing mechanism of the MWCNTs/PMMA composite thin films with various amounts of MWCNTs were explained by considering the composition and microstructures. The charge-transportation by the ions formed by electrolytic dissociation, their interactions with polymers, and the dimensions of the channels through which ions migrated were used to explain the sensing mechanism of the composite thin films of MWCNTs/PMMA doped with KOH. Other sensing characteristics, including linearity, sensitivity, response and recovery time, hysteresis and stability, were also investigated.