PEDOT multilayer LB films and their gas sensitivity based on quartz crystal microbalance

Multilayer ultrathin films of poly(3,4-ethylenedioxythiophene) (PEDOT)/stearic acid (SA) were fabricated using a modified Langmuir–Blodgett (LB) technique. The formation of LB ultrathin film was confirmed by UV–vis–NIR absorption spectrum and X-ray photoelectron spectroscopy (XPS) technique. The morphology of multilayer PEDOT/SA LB film was characterized by scanning electron microscopy (SEM). The results showed that small PEDOT grains were distributed in the polymeric LB film. The electrical conductivity of 40 layers as-prepared composite LB film was about 0.52 S cm−1, and conductivity varied from 10 to ca. 10−4 S cm−1 after the films were treated by HCl and NH3 gas alternately. The interaction or response of film coated QCM to NH3 has been investigated, which indicates that the QCM coated with composite film has fast response and recovery time to 10 ppm NH3 with good reversibility and recovery performance. At identical analyte concentration QCM sensitivity was enhanced with the increasing layer of LB film less than 80 layers, and the decrease of QCM sensitivity was observed in the case of layer number over 80 layers.