Diffusion of hard sphere fluids in disordered media: a molecular dynamics simulation study.

Area of Science:

• Physics
• Materials Science
• Computational Chemistry

Background:

• Understanding fluid behavior in confined or complex media is crucial for materials design.
• Hard sphere models provide a fundamental framework for studying dense fluid properties.
• Quenched disordered structures present unique challenges for predicting transport phenomena.

Purpose of the Study:

• To investigate the static and dynamic properties of hard sphere fluids within quenched hard sphere matrices.
• To determine the influence of fluid density, matrix density, matrix structure, and sphere size ratio on diffusion.
• To explore the relationship between matrix correlations and fluid particle dynamics.

Main Methods:

• Discontinuous molecular dynamics simulations were employed.
• System parameters varied included fluid and matrix densities, matrix generation methods, and fluid-to-matrix sphere size ratios.
• Analysis included static properties, self-diffusion coefficients, and single-chain structure factors.

Main Results:

• Matrix density has a greater impact on self-diffusion than fluid density, particularly at high matrix densities.
• The effect of fluid density on diffusion depends on the fluid-to-matrix sphere size ratio.
• Matrix generation methods significantly alter dynamic properties, even with similar static correlations.
• Heterogeneous diffusion and evidence of hopping mechanisms were observed at high matrix densities.

Conclusions:

• Matrix correlations play a critical role in the diffusion of fluid spheres.
• The geometric constraints imposed by the matrix structure are a dominant factor in fluid transport.
• Predicting diffusion requires considering both static structure and dynamic correlations within the matrix.