Gas sensing properties of mixed stearic acid/phthalocyanine LB thin films investigated using QCM and SPR

Metal free 2,3,9,10,16,17,23,24-Octakis(Octyloxy)-29H,31H Phthalocyanine and its derivatives containing zinc and copper have been used to fabricate thin films through the Langmuir-Blodgett (LB) Thin Film Fabrication technique. These highly ordered homogeneous, nanoscale thin films' characterization has been investigated using UV-Visible Spectrophotometer. The gas sensing properties of these thin films has been investigated using both Surface Plasmon Resonance (SPR) and Quartz Crystal Microbalance (QCM) Techniques. Several groups of volatile organic compounds including benzene and toluene (aromatic hydrocarbon) methanol and ethanol (alcohol) and chloroform, dichloromethane and carbon tetrachloride (chlorinated aliphatic hydrocarbons) have been used as analyte molecules. The sensor response of the thin films through interaction with the gas molecules has been analyzed in terms of dipole/dipole interaction or hydrogen bonding. It is seen that the analyte gas molecules with high refractive index show a higher response in the SPR technique compared to QCM. Also, a central metal atom effect on gas sensing has not been observed by the SPR technique while the experiments performed using the QCM technique showed that the central metal atom enhances the gas response.