Effect of pH on the properties of palmitic acid LB films for gas sensors

In this study, we fabricated the QCM with Langmuir–Blodgett (LB) film deposited at different subphase pH and investigated the resonant frequency response by the injection of organic gas response. In the π-A isotherm, the monolayer on the air/water interface had different limiting areas per molecule and showed more condensed status as increasing the subphase pH. When palmitic acid LB film was deposited on the QCM, the resonant frequency shift was proportional to the deposited layer and had more resonant frequency shift in the case of the higher pH range as expected. In the resonant frequency response for the injection of organic gas, frequency response has been improved in the case of LB film fabricated at the lower subphase pH range and dependent upon the molecular weight of organic gas. The frequency response of QCM for the injection of organic gases was mainly dependent upon the molecular weight of organic gas and the surface morphology of LB film.