PhD defence: Acoustic Response of Fluid Adsorption and Transport in Nanoporous Materials - Loriane Didier (PSM, LIPhy)

Fluid adsorption and transport in nanoporous materials are central to efficient technologies with important energy and environmental applications. Yet, while the structural, thermodynamic and transport properties of fluid in nanoporous materials are the subject of intense research, many aspects remain poorly understood. In particular, the acoustic signature of fluid confinement and adsorption in nanoporous solids still needs to be deciphered and rationalized. In this thesis, we explore the coupling at the nanoscale between fluid adsorption/transport and the acoustic properties of the host nanoporous material. Within the framework of statistical mechanics, we employ molecular dynamics simulations for a prototypical nanoporous material (an all-silica zeolite) filled with methane, carbon dioxide, and their mixture. First, we investigate the diffusion and permeability of these different fluids and show that the transport coefficients display either a monotonous or non-monotonous behavior upon increasing the fluid adsorbed amount. In the case of the fluid mixtures, we show that the miscibility/immiscibility – with potential nanosegregation effects – of the nanoconfined mixture play a key role. Second, we invoke the dynamic structure factor to investigate the acoustic properties of the zeolite subjected to fluid adsorption. By identifying the sound mode, we show that the fluid density significantly affects both the sound velocity and attenuation of the host zeolite. In particular, we develop simple physical models to rationalize the decrease in the sound velocity and increase in the sound attenuation upon fluid adsorption. Finally, we show that acoustic stimulation of the fluid-filled zeolite leads to a significant boost in both the fluid diffusion and permeability.