Characterization of Polymer Nanocomposite Thin Films Using Quartz Resonator Sensor

Thin films, especially polymer materials, as sensitive coating materials are wildly used in acoustic wave sensors for chemical and biological applications, and the responses of sensors commonly are regarded to the result of mass change. However, the mechanical properties of coating materials such as shear modulus also affect sensors in a more complicated way. It is therefore necessary to know the mechanical properties of films for design and analysis of sensors or other devices using the thin films. It is also expected that the measurement of responses of acoustic wave resonators coated with thin film materials would enable the characterization of thin film materials' properties that are otherwise difficult to probe. In this paper, the input electric impedance of four-layer thickness shear mode (TSM) quartz resonators (electrode/quartz/electrode/thin film coating) was derived using transfer matrix of transmission-line model (TLM). To characterize the shear modulus of carbon nanotube (CNT)-polymer nanocomposites, thin nanocomposite films of multi-wall carbon nanotubes (MWCNTs) in copolymers of poly(vinylidene fluoride) (PVDF-TrFE) were fabricated on TSM quartz resonators with spin coating. The resonator's parameters were extracted by fitting the theoretical curve to experimental admittance spectrum of the uncoated resonator. Shear moduli of PVDF-TrFE/MWCNTs nanocomposite thin films with MWCNTs 0.5wt%, 1wt% and 2wt% were extracted by fitting the theoretical curve to experimental admittance spectrum of the coated resonator. Both the storage modulus and the loss modulus were found to increase with the content of MWCNTs