Validation of quartz crystal rheometry in the megahertz frequency regime

The utility of the quartz crystal microbalance (QCM) as a high-frequency rheometer operating at 15 MHz was demonstrated. High-frequency data obtained from a series of rubbery materials were compared with results obtained from traditional dynamic mechanical analysis (DMA) at much lower frequencies. The high-frequency data enable meaningful shift factors to be obtained at temperatures much further above glass-transition temperature (T_g) than would otherwise be possible, giving a more complete picture of the temperature dependence of the viscoelastic properties. The QCM can also be used to quantify mass uptake and changes in viscoelastic properties during sample oxidation. The viscoelastic response spanning the full range of behaviors from the rubber to glassy regimes was found to fit well with a six-element model consisting of three power-law springpot elements. One of these elements is particularly sensitive to the behavior in the transition regime where the phase angle is maximized. The value of this quantity is obtained from the maximum phase angle, which can be obtained from a temperature sweep at fixed frequency, proving a means for more detailed frequency-dependent rheometric information to be obtained from a fixed-frequency measurement at a range of temperatures.