Preparation, fabrication and response behavior of a HTBN/TDI/MWCNT composite sensing film by in situ dispersed polymerization

A polyurethane inserted multi-wall carbon nanotube (MWCNT) composite conductive film was prepared by in situ dispersed polymerization reaction using hydroxyl-terminated poly(butadiene-acrylonitrile) liquid rubber as a linear diol, toluene diisocynate as a curative, ethylene glycol or glycerine or triethanolamine as a chain-extending agent and MWCNT as a conducive filler. The effect of various curing temperatures and chain-extending agents on vapor-induced electrical responsiveness of the conductive films was investigated. The structural characterization of the cured film was conducted by Fourier transformation infrared spectrophotometer (FTIR), differential scanning calorimeter (DSC), polarization microscope (POM) and wide angle X-ray diffraction (WAXD). The experimental results showed that the conductive composite film obtained in the present work exhibited a microphase separation resulting from the soft-hard segment domains, and possessed some crystalline behavior from the hard segment. The response intensity was enhanced with the curing temperature increased, while the reversibility could be improved at a relatively low curing temperature. The responsivity of the film produced by a linear difunctional group chain-extending agent was lower than that prepared by trifunctional group curatives, and the reversibility was vice versa. The experimental phenomena were explained from the viewpoint of the microphase separation, crystalline behavior, the structural characteristics of the soft-hard segment, and the electronic properties of multi-wall carbon nanotubes as well as a weak electrostatic or noncovalent interaction between polymer or analyte molecules and MWCNTs.