Acoustic Response of Fluid Adsorption and Permeation in Nanoporous Materials – ACOUFEN

Fluid adsorption and transport in nanoporous materials are at the heart of efficient technologies impacting our economy/ecology: energy storage/conversion, environment protection, health/human welfare, agribusiness/food science, etc. In particular, nanoporous solids shaped as membranes are expected to play a leading role in the “seven key chemical separations to change the world” but also to address increasingly complex problems such as bio/agropollutants removal, greenhouse gas mitigation, drinkable water production, etc. Yet, despite a promised bright future, with more and more separation/catalytic processes to treat, the design of efficient nanoporous membranes is hampered by difficulties in extending their use to severe conditions [e.g. high temperature/pressure, harsh environments, and irradiation]. In practice, extending applications to extreme conditions requires on-line monitoring of material integrity and fluid adsorption/flow (to detect early any material modification or process malfunction). In this context, despite its generalized use in materials science, acoustics is often assumed to be unsuited for nanophenomena due to their large wavelength. Yet, the adsorption/permeation footprint of a nanoconfined fluid is included in an average way in the signal emitted by the system subjected to fluid pressure or acoustic excitation.

This project will employ an experimental, molecular modeling and theoretical approach – from the atomic to the macro scales – to unravel the acoustic signature of adsorption/transport in nanoporous materials. At each scale, experimental and theoretical techniques will probe spontaneous acoustic emission by the fluid/solid system and its response to acoustic wave stimulation. Fluids with different interactions (He, N2, CH4, CO2) will be studied in nanoporous materials (zeolites and other metal oxyde ceramics) to probe pore size/interaction effects at similar surface chemistry (oxide). By varying, statically or dynamically, the pressure gradient inducing flow and the mean pressure/temperature, the role of transport type (Knudsen, diffusion, viscous flow) and adsorption type (partially and entirely filled pores) will be probed. Using a joint experimental/theoretical study, the acoustic properties of the solid/fluid systems will be probed at the molecular (?nm/THz), mesoscopic (~micron/GHz), and macroscopic (~mm/MHz) scales. At each scale, the theoretical predictions will be compared with the experimental data to obtain a bottom-up description of the acoustics of adsorption/transport in nanoporous solids. As a final objective, we also include a work package aiming at testing the possible use of acoustic stimuli to modulate fluid adsorption and transport in a nanoporous solid.

This multiscale strategy, relying on experiment, theory, and molecular simulation, will allow identifying the acoustic footprint of gas adsorption/permeation in nanoporous solids. The objectives are two-fold. (1) Unravel the coupling between adsorption/transport phenomena and acoustic response to pave the way for acoustic operando monitoring. This fundamental approach falls in the broad range of wave/matter interactions but to our knowledge this is the first time that the coupling between acoustic waves and microscopic adsorption/transport phenomena in nanoconfined fluids is considered. (2) Explore the use of this coupling to control gas separation in nanoporous materials. If successful, the present project could lead to a novel gas separation method based on acoustic swing adsorption (i.e. when the porous material is saturated, regeneration/desorption is achieved by applying an acoustic wave). In this context, we emphasize that ACOUFEN is a fundamental research project (PRC) involving experimental and theoretical tools to provide microscopic and macroscopic insights into the acoustic response of fluid in nanoporous materials. Yet, despite its fundamental nature, this project could lead to groundbreaking applications.