Ultrasonic rheology
In principle, the visco-elastic compression and shear moduli of a material can be deduced from the measurement of the propagation speed and the attenuation of longitudinal and transverse waves. Such measurements are difficult to perform in soft materials at ultrasonic frequencies because of the strong attenuation of these waves as well as the strong impedance contrasts between the materials and the piezoelectric transducers. We have developed a technique for measuring the viscoelastic shear modulus at metrological level in the megahertz range on thin samples.
Characterization of viscoelastic liquids – In collaboration with Gauthier Lefebvre and Tony Valier-Brasier (Institut d'Alembert), we have determined the shear modulus of a viscoelastic liquid, a commercial couplant (SWC-2 from Olympus) used for ensure the contacts for shear measurements, and thus showed that it had a shear modulus comparable to that of Plexiglas in the megahertz range, which explains its performance as a coupling agent!
G. Lefebvre, R. Wunenburger, T. Valier-Brasier, Ultrasonic rheology of visco-elastic materials using shear and longitudinal waves, Applied Physics Letters 112, 241906 (2018).
Characterization of “hard” solid polymers – In collaboration with Simon Alverède (PhD student), Gauthier Lefebvre and Tony Valier-Brasier (Institut d'Alembert), we showed that this technique could be applied to hard solids. This challenge was met by making the contacts at the interfaces reproducible.
A. Simon, G. Lefebvre, T. Valier-Brasier, R. Wunenburger, Viscoelastic shear modulus measurement of thin materials by interferometry at ultrasonic frequencies, Journal of the Acoustical Society of America 146, 3131 (2019).
Characterization of “soft” solid polymers – In collaboration with Quentin Baudis (PhD student) and Tony Valier-Brasier (Institut d'Alembert), we showed that this technique could also be applied to soft and very attenuating solids. This challenge could be met by employing samples of sub-wavelength thickness.
Q. Baudis, R. Wunenburger, T. Valier-Brasier, Ultrasonic rheology of soft, visco-elastic materials: example of crosslinked Polyurethane elastomer, submitted to Journal of Acoustical Society of America (2022).