Speaker
Description
Fluids confined in nanoporous media exhibit dynamical and thermodynamic properties that can differ markedly from their bulk counterparts due to restricted geometry, interfacial effects, and modified intermolecular interactions. Aqueous electrolyte solutions represent a particularly rich class of confined fluids, where ion hydration and ion–water coupling introduce additional complexity. In this contribution, we investigate the molecular dynamics of glass-forming LiCl aqueous solutions (LiCl·6H2O) in bulk and under nanoconfinement in mesoporous silica matrices (SBA-15 and MCM-41, pore sizes 4 - 8 nm).
The study combines differential scanning calorimetry (DSC), Raman spectroscopy, broadband dielectric spectroscopy, nuclear magnetic resonance (NMR), and quasi-elastic neutron scattering (QENS) to probe confinement effects across complementary time and length scales. DSC reveals an increase in the glass transition temperature under confinement, while Raman spectroscopy evidences a strong perturbation of the hydrogen-bond network induced by LiCl that persists in nanopores. Dielectric spectroscopy shows a systematic reduction of ionic dc-conductivity in confined systems. NMR measurements also indicate that nanoconfinement does not alter the temperature at which the T₁ relaxation minimum occurs.
To directly access microscopic dynamics, QENS experiments were performed on the IN13 backscattering spectrometer (ΔE ≈ 8 µeV) at ILL, using elastic fixed window scans (EFWS) to extract mean square displacements and inelastic fixed window scans (IFWS) to characterize translational dynamics via Arrhenius and jump-diffusion models. QENS results show that bulk LiCl solutions exhibit diffusion coefficients significantly lower than bulk water, reflecting strong ion–water coupling in the glass-forming regime. Under confinement, the effect on translational diffusion is moderate. For water confined in SBA-15, diffusion coefficients differ from bulk values by ~20%. A comparable relative variation is observed for LiCl solutions; however, given the resolution of IN13 for low values of the transfer of momentum, a precise quantitative determination of confined electrolyte diffusion remains limited.
These results indicate that nanoconfinement induces clear changes in thermodynamics and local dynamics, while its impact on translational diffusion in concentrated LiCl solutions remains relatively weak. The findings provide molecular-level constraints for modeling transport and relaxation in confined electrolytes relevant to natural and engineered nanoporous systems.
| Country | France |
|---|---|
| Student Awards | I would like to submit this presentation into the Earth Energy Science (EES) and Capillarity Student Poster Awards. |
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