Recognition of alcohol vapor molecules by simultaneous measurements of resistance changes on polypyrrole-based composite thin films and mass changes on a piezoelectric crystal

A novel gas sensor is fabricated on the basis of simultaneous measurements of resistance changes on polypyrrole-based composite thin films and frequency changes on a piezoelectric crystal. Molecular species such as ethanol and methanol can be recognized by the (ΔR/Δf) values, where ΔR and Δf are the resistance and frequency change, respectively. The ΔR/Δf value remaining constant at various concentrations of detected gases is a characteristic index of a given kind of vapor molecules. The ΔR/Δf value can be modified by the introduction of inert materials, including poly(ethylene oxide) (PEO) and polyacrylonitrile (PAN), into the conducting polymer matrix. The higher the ΔR/Δf value, the better is the recognition ability. The composite PPy/PEO (PEO=7 g/l) film exhibits the best recognition for alcohol vapor molecules among the investigated sensing films. Meanwhile, the quantitative analysis of the vapor molecules can be achieved by measuring the ΔR or Δf values.