Layered Fluid Structure and Anomalous Diffusion under Nanoconfinement

Area of Science:

• Physical Chemistry
• Materials Science
• Nanotechnology

Background:

• Molecular diffusion behavior deviates significantly under nanoconfinement compared to bulk fluids.
• Understanding these deviations is crucial for designing nanoscale devices and materials.

Purpose of the Study:

• To elucidate the influence of boundary layering on the self-diffusion of confined fluids.
• To quantify the relationship between layering and anomalous diffusion dynamics.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model fluid behavior.
• Molecular mechanics arguments were used to analyze the simulation results.

Main Results:

• Anomalous diffusion is controlled by the degree of layering, quantified by the Wall number (Wa).
• At Wa ≳ 1, significant layering restricts fluid dynamics, necessitating thermally activated hopping for movement.
• Diffusivity can be approximated as a weighted average of bulk and first-layer diffusivities.

Conclusions:

• The Wall number (Wa) effectively predicts the impact of layering on diffusion.
• Layering-induced deviations from bulk diffusion can be quantified based on confinement length scale.