A high-frequency piezoelectric rheometer with validation of the loss angle measuring loop: application to polymer melts and colloidal glasses

We revisit and improve the technique of piezo-operated sliding-plate rheometry in order to provide a versatile platform for measuring the linear viscoelastic properties of various soft matter systems at frequencies from 10 to 1.000 Hz. The sensitive loss angle measuring loop is validated explicitly against reference data from entangled amorphous polymer melts obtained with conventional rotational rheometers by means of time-temperature superposition (tTS). Frequency range limiting factors such as sample and tool inertia are discussed while errors are traced and theoretical correction is shown to be feasible when strong nonlinear behavior of the measuring cell is present. This gives confidence in measuring more complex systems where tTS does not apply. We also demonstrate the ability to probe the short-time dynamics of hard-sphere colloidal glasses. Important high-frequency features such as the behavior of the elastic modulus, G′, the moduli crossover frequency fc related to β-relaxation, and the associated limiting in-phase (with strain-rate), dynamic viscosity η∞′, are captured. This validates the suitability of this high-frequency rheometric technique to provide insights into interactions at nanometric particle separations.