Does confining the hard-sphere fluid between hard walls change its average properties?

Area of Science:

• Statistical Mechanics
• Soft Matter Physics
• Computational Chemistry

Background:

• Density functional theory (DFT) often focuses on fluid structuring near confining walls.
• Understanding confined fluid behavior is crucial for materials science and nanotechnology.

Purpose of the Study:

• To precisely quantify thermodynamic and kinetic properties of hard-sphere fluids under confinement.
• To investigate the effect of wall-induced structuring on average fluid properties.
• To identify conditions where confinement significantly alters fluid behavior.

Main Methods:

• Grand canonical transition-matrix Monte Carlo simulations.
• Discontinuous molecular dynamics simulations.
• Analysis of equilibrium hard-sphere fluid confined between smooth hard walls.

Main Results:

• Inhomogeneous fluid structuring has a negligible effect on average properties across a broad range of conditions.
• A simple analytical equation relates confined fluid density to bulk fluid density at equal activity.
• Dense fluids confined to <3 particle diameters exhibit in-phase oscillations in excess entropy and self-diffusivity.

Conclusions:

• Confinement effects are minimal except for dense fluids in narrow gaps (<3 particle diameters).
• Observed deviations are attributed to geometric packing frustration and layer formation.
• The findings provide a simplified model for confined fluids and highlight specific conditions for significant deviations.