Stabilizing the hexagonal close packed structure of hard spheres with polymers: Phase diagram, structure, and...

Area of Science:

• Colloid science
• Statistical mechanics
• Materials science

Background:

• Investigating binary mixtures of colloidal hard spheres and polymer chains is crucial for understanding complex fluid behavior.
• Previous work predicted stabilization of the hexagonal close-packed (HCP) structure in such mixtures due to polymer-void interactions.

Purpose of the Study:

• To accurately determine the phase diagram of a binary mixture of colloidal hard spheres and freely jointed polymer chains.
• To verify and refine predictions regarding the stability of the hexagonal close-packed (HCP) phase in colloidal-polymer mixtures.

Main Methods:

• Utilizing advanced Monte Carlo simulations to model the system.
• Performing comprehensive free-energy calculations for the entire binary mixture.
• Analyzing the structure and dynamic behavior of the mixtures.

Main Results:

• A broad fluid-solid coexistence region was identified.
• A metastable gas-liquid coexistence region was observed.
• The HCP phase was found to be stable only within a narrow window of high polymer reservoir packing fractions, with the coexisting HCP phase being nearly close-packed.

Conclusions:

• The stability of the HCP phase in colloidal-polymer mixtures is highly sensitive to polymer reservoir packing fraction.
• The findings refine the understanding of phase behavior in these complex systems and highlight the importance of accurate free-energy calculations.