Polyaniline films deposited by anodic polymerization: Properties and applications to chemical sensing

Abstract

Polyaniline conductive thin films have been used for the detection of a number of important gases and vapors: organic solvents, ammonia, oxygen, hydrogen sulfide, nitrogen and sulfur oxides. The films can be produced by spin coating, thermal evaporation, the Langmuir–Blodgett technique and cyclic voltammetry. This paper presents preliminary results on acidity sensing with electrodeposited polyaniline layers. Polyaniline conductive thin films were prepared by anodic polymerization from an acidic solution of the monomer on two kinds of substrates: gold plated silicon and indium-tin oxide on glass. Ultraviolet-visible (UV-VIS) spectrometry of layers showed a maximum absorption peak around 800 nm for all the samples investigated (independent of preparation conditions) and revealed that the polymeric films were in the emeraldine base form, 18–25% protonated. The room-temperature in-plane d.c. conductivities of the polymer films were found to be between 4×10⁻⁹ S cm⁻¹ and 9×10⁻¹⁰ S cm⁻¹ (deposition rate approximately 4 μm h⁻¹; film thickness 750–1100 nm). Immersion of the polyaniline films in dilute hydrochloric solution resulted in changes in the d.c. conductivity by up to nine orders of magnitude, reaching a value of 4×10⁻² S cm⁻¹ while immersed in the acidic solution. Humidity tests carried out by exposing polyaniline samples to water vapors changed the d.c. conductivity by one order of magnitude to 1.34×10⁻⁸ S cm⁻¹.