The research performed during the NanoSep project aimed to elucidate the behavior and properties of fluids confined in nanoporous and interfacial environments using advanced molecular dynamics simulations. The studies addressed fundamental questions related to molecular exchange dynamics, interfacial interactions, and their implications for macroscopic properties, such as NMR relaxation rates and interfacial ethanol enrichment.
The first phase of the research project (corresponding to WP1 in the original proposal) focused on understanding the behavior and properties of fluids confined within nanoporous and interfacial environments through advanced molecular dynamics simulations. The primary goal was to establish a molecular-level understanding of how fluid dynamics, molecular exchange, and interfacial interactions influence macroscopic properties such as NMR relaxation rates and ethanol enrichment at interfaces.
In a first study, published in collaboration with Benoit Coasne, the role of hydrophobic and hydrophilic interactions in water-ethanol mixtures near planar organosilica surfaces was explored using molecular simulations [Gravelle and Coasne, hal-04917234, Submitted to Open Research Europe]. Organosilica surfaces, with their tunable hydrophobicity achieved by varying the ratio of methyl and hydroxyl groups, were shown to promote ethanol enrichment at the interface. Molecular dynamics simulations revealed that surfaces decorated with methyl groups exhibit significant preferential adsorption of ethanol, consistent with prior observations on graphite. This study also examined how surface roughness and the spatial organization of functional groups impact interfacial ethanol enrichment. These findings are particularly relevant for designing cost-effective, organosilica-based membranes for water-ethanol separation, presenting a promising alternative to carbon-based materials.
In parallel, a study conducted with Benoit Coasne and collaborators from the Institute for Computational Physics (ICP) in Stuttgart employed atomistic molecular dynamics simulations to investigate water confined in slit nanopores. The study highlighted how molecular exchange dynamics between surface-adsorbed layers and the bulk fluid influence NMR relaxation rates. Using first return passage time calculations, the adsorption time, pore size, and diffusion coefficient were linked to the relaxation behavior. This approach provides a predictive framework for understanding molecular relaxation at interfaces using principles of statistical mechanics.
Additionally, the research carried out in this first work package proved exceptionally productive and unexpectedly insightful, leading to new collaborations that resulted in two additional publications.
- The first study [Asha, Jamal, Gravelle, Mayes, and Shen, The Journal of Physical Chemistry B] investigated the role of minor water content in solid-state polymer electrolytes (SPEs), revealing how slight hydration enhances ionic conductivity while preserving mechanical integrity in polymers such as poly(ethylene oxide) (PEO) and poly(lactic acid) (PLA) when combined with lithium perchlorate (LiClO₄). The molecular dynamics code developed for the NanoSep project was extended to describe the transport properties of ions within polymer matrices, which was of interest to Professor Shen’s group (University of Massachusetts Dartmouth).
- The second study [Hayatifar, Gravelle, Moreno, Schoepfer, and Lindsay, Geochemical Transactions] focused on interfacial processes in ferrihydrite-water systems, employing reactive molecular dynamics simulations and synchrotron X-ray spectroscopy to elucidate the dynamics of surface restructuring, charge equilibration, and hydrogen bond networks.
Both of these studies are directly connected to the core themes of this work package, further extending its scientific impact. To help the Researcher develop independent research activities, the Supervisor was not involved in these works.
Building on the molecular dynamics results obtained during WP1—particularly those from publication hal-04917234—two possible models for upscaling the results to the mesoscale (WP2) and macroscale (WP3) were investigated. While these results remain unpublished, they are promising and have formed the basis for securing a follow-up grant (ANR JCJC). This grant, awarded to the Researcher, will enable direct continuation of the work initiated during the MSCA NanoSep project over the next four years. This will be achieved, in part, through the hiring of a postdoctoral researcher and a PhD student.
