Solvent-mediated forces in critical fluids.

Area of Science:

• Soft matter physics
• Statistical mechanics
• Physical chemistry

Background:

• Understanding fluid-wall interactions is crucial for colloid science.
• Supercritical fluids exhibit unique phase behavior near critical points.
• Density functional theory (DFT) is a powerful tool for studying fluids.

Purpose of the Study:

• To investigate the effective interaction between planar walls in a supercritical fluid.
• To analyze the fluid's behavior in the critical region using a hard-core Yukawa model.
• To develop and compare theoretical approaches for critical phenomena.

Main Methods:

• Utilizing a formulation of the weighted density approximation (WDA) combined with hierarchical reference theory (HRT).
• Incorporating methods capable of handling critical long-wavelength fluctuations.
• Comparing the developed approach with existing theoretical models.

Main Results:

• Observed a temperature-dependent change in wall-fluid interaction character.
• Noted the smoothing of molecular layering oscillations with decreasing temperature.
• Identified a long-range attractive tail near the critical point, consistent with the critical Casimir effect.
• Found significant corrections to scaling at low reduced temperatures.

Conclusions:

• The critical Casimir effect governs wall interactions in supercritical fluids near critical points.
• The developed theoretical framework accurately captures critical phenomena.
• Findings have implications for colloidal particle aggregation in critical solvents.