Gas-sensing properties of poly(p-xylylene) - titanium thin film nanocomposite, prepared by vapor deposition polymerization

•Thin poly(p-xylylene)-based nanocomposite films containing titanium were proposed as a sensitive layer of gas sensors.•The air composition was found to influence on the electric characteristics of these films.•Sensitive parameters are: dc and ac conductance, capacitance at different frequencies, time of current decay•The unique set of parameters for given atmosphere composition allows to solve gas sensor selectivity problem Poly(p-xylylene) – titanium thin film nanocomposites were synthesized by vacuum deposition polymerization and proposed to serve as a gas sensor. They can reversibly and selectively detect several parts per thousand water, ethanol and even n-propyl benzene vapors with short response time. The presence of polar molecules affects conductance and capacitance, while nonpolar vapors such as benzene and toluene have no effect on electrical properties. Polarization and depolarization currents were recorded and it was found that composition of gaseous medium affected the parameters of dielectric response function. The frequency dependences of complex capacitance were fit by the Debye equations; correlations of the fit parameters and titanium concentration, as well as dipole moment of analyte molecules in atmosphere were found. The model was proposed, that explains dielectric behavior of nanocomposites and assumes the existence of several dielectric relaxation processes with different characteristic times: orientation of physically adsorbed polar molecules, charge exchange of surface states, generated by chemisorbed molecules at the interface nanoparticle/polymer matrix and Maxwell-Wagner interfacial polarization phenomena.