Interaction phononique à longue portée induite par mouillage d'une interface hydrophile modèle

Fluid mechanics, based on the continuum hypothesis, accurately encapsulated macroscopic flows. Concepts such as surface tension and Young's law allow us to distinguish between the hydrophilic or hydrophobic character of the solid-liquid interaction with a given surface. This interaction is key for rheological measurements. General fluid behaviour is modeled through the viscous and elastic responses to a mechanical solicitation. The dominant rheological model is that of Maxwell. It identifies a relaxation viscoelastic timescale. Frenkel later proposed a molecular physical explanation for simple liquids. This model predicts shear elastic liquid behaviour at very high frequencies. Nonetheless, in the last few decades, experimental results have highlighted that this model breaks down when liquids are confined. A shear elastic behaviour is then observed at low-frequency, from the nanoscale to the mesoscopic scale, proving the ability of the liquid to transmit a shear elastic wave.To observe this shear elastic behaviour, a necessary condition is that the solid-liquid interaction is highly wetting, therefore optimising the mechanical transfer from the surface to the liquid. These results on liquid shear-elasticity have led to new theoretical frameworks (e.g. k-gap model). Nonetheless, the role of the solid has been until now overlooked. Since liquids can propagate vibrational states over long ranges when in contact with high energy surfaces, this thesis studies whether these vibrational states interact with the solid's bulk phonons, and propagate far from the surface. Using X-ray and neutron diffraction techniques, we highlight a phononic interaction between water and α-Al₂O₃ (highly wetting monocrystal). The bulk acoustic phonons (hundreds of microns from the interface), are perturbed by the flowing liquid. A broadening of acoustic phonons, and curiously, a hardening of transverse and longitudinal acoustic phonons are observed. Hardening and broadening are isotope dependent, with heavy water showing a lesser interaction. Furthermore, using Raman-X and high resolution diffraction techniques, no chemical or structural changes were observed, suggesting our results correspond to a purely vibrational anharmonic dynamic interaction between a liquid and a solid. This interaction depends on observed Brillouin zones, and cannot be considered as a surface interaction only. The mechanical coupling that extends deep into the bulk results from a non-equilibrium state induced by a flowing liquid, calling for new theoretical frameworks to describe this coupled phononic state, integrating new liquid properties such as mesoscopic shear elasticity.