Bulk rheometry at high frequencies: a review of experimental approaches

Abstract

High-frequency rheology is a form of mechanical spectroscopy which provides access to fast dynamics in soft materials and hence can give valuable information about the local scale microstructure. It is particularly useful for systems where timetemperature superposition cannot be used, when there is a need to extend the frequency range beyond what is possible with conventional rotational devices. This review gives an overview of different approaches to high-frequency bulk rheometry, i.e. mechanical rheometers that can operate at acoustic (20 Hz-20 kHz) or ultrasound (> 20 kHz) frequencies. As with all rheometers, precise control and know-how of the kinematic conditions are of prime importance. The inherent effects of shear wave propagation that occur in oscillatory measurements will hence be addressed first, identifying the gap and surface loading limits. Different high-frequency techniques are then classified based on their mode of operation. They are reviewed critically, contrasting ease of operation with the dynamic frequency range obtained. A comparative overview of the different types of techniques in terms of their operating window aims to provide a practical guide for selecting the right approach for a given problem. The review ends with a more forward looking discussion of selected material classes for which the use of high-frequency rheometry has proven particularly valuable or holds promise for bringing physical insights.

Revisiting impulsive stimulated thermal scattering in supercooled liquids: Relaxation of specific heat and thermal expansion

“…It is interesting to notice that both the real and imaginary part undergoes a transition around 280 K, which is a reflection of the strong coupling between the acoustic motion and structural changes of the network when 1/f A being of the order of the structural relaxation time. This feature provides a way to study the mechanical relaxation by performing measurements at numerous grating spacings in a broad range [4], namely a mechanical spectroscopic analysis like the traditional rheological spectroscopy [3] or ultrasonic spectroscopy [43,44]. In addition to the mechanical relaxation dynamics, the models developed in this work enable the individual and simultaneous determination of the heat capacity C and the thermal expansion coefficient γ relaxation.…”

Viscoelasticity, Like Forces, Plays a Role in Mechanotransduction

“…The third regime represents a higher-frequency transition regime (a viscoelastic solid). The fourth is a high-frequency jamming regime (a viscoelastic solid) ( Figure 2 ) ( Liu et al, 2010 ; Schroyen et al, 2020 ). There are minimally two or perhaps even three regimes ( Stamenović, 2006 ).…”

Applicability of the Cox-Merz Rule to High-Density Polyethylene Materials with Various Molecular Masses

“…. γ true at the wall, we applied the Weissenberg-Rabinowitsch correction Equation ( 6) [36], and the shear viscosity was then calculated by Equation (7). The measurement range of the shear rate of the extrusion rheometer was between 25 and 300 s −1 .…”

“…Other methods are based on oscillatory measurements using, for instance, plate-plate and cone-plate rheometers. The big advantages of oscillatory over pressure-driven approaches are that they are fast, cheap, and easy to use [7]. Additionally, a relatively small amount of material is needed, and low shear rates Polymers 2021, 13, 1218 2 of 13 can be measured.…”