Isostructural solid-solid transitions in binary asymmetrical hard sphere system: based on solvent-mediated potential.

Area of Science:

• Statistical mechanics
• Condensed matter physics
• Physical chemistry

Background:

• Solvent-mediated potentials (SMP) are crucial for understanding interactions in solutions.
• Existing theories often lack accurate predictions for systems with significant size asymmetry.
• Hard sphere models provide a fundamental framework for studying phase behavior.

Purpose of the Study:

• To develop an improved semi-analytical theory for calculating solvent-mediated potentials (SMP) in hard sphere systems.
• To investigate size-dependent phenomena, including isostructural solid-solid transitions in binary asymmetrical hard sphere mixtures.
• To determine the critical size asymmetry ratio for these transitions.

Main Methods:

• Modification of a bridge functional within a semi-analytical hard sphere reference system theory.
• Calculation of SMP for large particles in a solvent bath of smaller particles.
• Application of a single-component macrofluid approximation combined with the improved theory to study phase transitions.

Main Results:

• The improved theory accurately predicts SMP for large hard spheres in a small hard sphere solvent, aligning with fitting formulas.
• Isostructural solid-solid transitions were observed in binary asymmetrical hard sphere systems.
• The critical size asymmetry ratio for these transitions was found to be approximately 1/8.
• Increasing size asymmetry affects the critical densities for face-centered cubic (fcc) transitions differently for large and small particles.

Conclusions:

• The enhanced theory provides a reliable method for calculating SMP in size-asymmetric hard sphere systems.
• Size asymmetry is a key factor driving isostructural solid-solid transitions in binary mixtures.
• The findings offer insights into the phase behavior of dense colloidal and molecular systems.