Preparation and Properties of Conducting Polymeric Ultrathin Films

A multilayer ultrathin film of poly(3,4-ethylene dioxythiophene) (PEDOT) was first prepared by a modified Langmuir- Blodgett (LB) technique. The polymerization of PEDOT monomer occurred in a multilayer as-prepared LB film by exposing the film to EDOT vapor. The formation of PEDOT particles in the LB film was confirmed by UV-Vis-near IR (UV-Vis-NIR) absorption spectrum and X-ray photoelectron spectroscopy (XPS). By using scanning electron microscopy (SEM), investigation on the film surface exhibited small PEDOT particles distributed in stearic acid (SA) LB films. Secondary ion mass spectrometry (SIMS) was employed to analyze the location of PEDOT formed and the results showed that PEDOT was well confirmed in the multilayer structure. A 60-layer PEDOT LB film had higher conductivity (2.6 S·cm−1) than a conventional PEDOT film, and exhibited excellent doping/dedoping characteristics. An investigation on the relationship between film conductivity and exposure time on EDOT ambience revealed that the film obtained steady conductivity after 120 min and it was concluded that lower oxidizer density in LB film might slow the polymerization speed of EDOT. In a study of sensitive characteristics, the PEDOT film showed faster and nonlinear responses to analyte gas in a lower concentration (ϕ<30×10−6), and exhibited a linear response to analyte in a higher concentration (ϕ=(30-120)×10−6). The result of gas sensitivity also showed that the film had excellent reversible and reproducible response to HCl vapor. The mechanism of conductivity and gas sensitivity of composite LB films was also included.