Determination of the viscoelastic properties of polymer films using a compensated phase-locked oscillator circuit

Using a combination of the quartz crystal microbalance and a corresponding physical model for the compound resonator, the viscoelastic properties of polymer films have been studied. By using a compensated phase-locked oscillator system, both resonant frequency and resistance (motional resistance of the Butterworth-Van Dyke equivalent circuit) can be measured simultaneously. The behavior of resistance as a function of film thickness or corresponding frequency shift provides a means not only for quantitatively determining the shear viscosity and elastic modulus of films but also for qualitatively comparing various systems. The physical model is extended to include four layers for describing dissolving/swelling films that form an energy-dissipative, interfacial layer. If the underlying film is rigid and acoustically thin, then the four-layer case can be reduced to a simplified three-layer description.