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Anisotropic molecular diffusion in confinement II: A model for structurally complex particles applied to transport in
Kevin Höllring1, Andreas Baer1, Nataša Vučemilović-Alagić2
1PULS Group, Institute for Theoretical Physics, FAU Erlangen-Nürnberg, Cauerstraß e 3, 91058, Erlangen, Germany.
Journal of Colloid and Interface Science
|December 3, 2023
Summary
We developed a new method to study diffusion in confined spaces, revealing how ionic liquids behave differently at various interfaces. This helps understand complex fluid dynamics in nanoconfined systems.
Area of Science:
- Physical Chemistry
- Materials Science
- Chemical Engineering
Background:
- Diffusion in confined environments is crucial for applications like supported liquid phases.
- Understanding spatially dependent diffusion coefficients, especially for nanometric species, remains a challenge.
- Existing methodologies struggle with systems where structural fluctuations and diffusion occur on similar timescales.
Purpose of the Study:
- To develop a universal methodology for analyzing complex, coupled dynamics of diffusion in confinement.
- To resolve spatially dependent diffusion coefficients parallel and perpendicular to interfaces.
- To investigate the dynamics of large, flexible species without assuming timescale separation.
Main Methods:
- Utilized a model based on the 2-dimensional Smoluchowski equation and systematic coarse-graining.
- Applied the method to Molecular Dynamics simulations of bulk ionic liquid systems.
- Validated the approach on systems with varying cation sizes and internal degrees of freedom.
Main Results:
- Demonstrated the anisotropic nature of diffusion coefficients at interfaces.
- Showed that spatial variations in diffusivity are linked to interface-induced structuring of ionic liquids.
- Observed consistent but distinct length scale variations at solid-liquid and liquid-vapor interfaces in confined ionic liquids.
Conclusions:
- The developed model successfully captures and analyzes complex diffusion dynamics in confined systems.
- The study provides a new interpretation of experimentally observed diffusion constants in bulk liquids.
- Highlights the significant impact of interfaces on the diffusion behavior and structuring of ionic liquids.
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