Emmanuel Caplain

Viscosimetry using a new electromagnetic‐acoustic microbalance

The nanostructure evolution of gels, biomaterials or porous media can be characterized by its mechanical properties. Few nondestructive techniques are developed to investigate the viscosity evolution. This paper present a new electromagnetic‐acoustic technique using a wireless thickness shear mode transducer. A suitable model of the measurement is also presented to characterize the viscosity of the nanostructure in contact with the transducer. This transducer is a double copper‐clad PVDF substrate resonator, designed to operate over a wide radiofrequency range without lumped tuning capacitors. This architecture constitutes an alternative solution to design a high‐Q ultrasonic microbalance. To characterize the material at the surface of the transducer, the evolution of the induced complex impedance is measured. From this evolution, the mechanical energy storage and dissipation in the material can be extracted. In order to validate the lumped element model used, a series of glycerol/water mixtures is studie...

Dry coupling ultrasonic high frequency (10-100 MHz) sensors for detection of surface and tribological properties at a submicrometric scale

Acoustic plane sensors adequately pressed against materials are suitable to measure elastic constants from flight-time measurement, without any coupling fluid for high temperature, with longitudinal and transverse acoustic waves in the megacycle range. Soft delay lines are generally used to match the sample roughness and to make mechanical play correction easier. At the opposite, our sensors use a hard delay line with a mirror-polished end surface. An experimental set-up is presented to perform acoustic reflection measurement in various contact conditions by increasing the applied mechanical load. The frequency dependence of this parameter is also measured in the 10- to 100-MHz range. Reproducibility tests are presented to validate this experimental set-up, but the main results concern the surprising ability of this technique to detect surface property modifications limited to thickness less than 1 μm. Indeed, surface modification induced by different solvents on glass substrates has been detected by this means. This technique has also been used to detect surface property modifications of lixiviated glasses. In this case, atomic force microscopy and inductively coupled plasma analyses have demonstrated that the earlier stage of the surface damage had been detected whereas the thickness altered by ionic diffusion was less than 100 nm with almost no roughness variation. Similarly, tests on mechanically scratched glasses have shown that samples with an average roughness, respectively, of 4 and 120 nm were easily identified from their reflection coefficient versus load curves. Moreover, the pressure dependence of the acoustic reflection is used to estimate the contact stiffness and the contact area between the sensor and the material as a function of the applied compressive stress for contact, adhesion, and friction investigations.

Effects of materials conductivity on the viscosity measurement using a QCM

Quartz crystal microbalance (QCM) is commonly used to characterize the viscosity of soft materials. For biomedical applications the modified BVD model of QCM is unsuitable due to the conductivity of the biomaterial. In order to take into account the electrical effects, a new model including a static lossy capacitor is proposed. A theoretical study of the shear wave propagation in the quartz shows that these effects modify the static and the motional branches of the BVD circuit. The conductivity effects of the material at the surface of the QCM can be modeled by same parallel elements added in both branches. In the motional branch the electromechanical coupling factor is applied to these elements. To validate the new lumped element model measurements for KCl mixtures are achieved. The results show that an accurate extraction of viscosity (<5%) can be obtained for a middle of conductivity less than 0.3 S/m. In addition for water/glycerol mixtures the resonant frequency shift and damping follow an accurate l...