Polymorphism and Perfection in Crystallization of Hard Sphere Polymers

Area of Science:

• Materials Science
• Polymer Physics
• Computational Chemistry

Background:

• Understanding polymer crystallization is crucial for materials design.
• Spontaneous crystallization of long polymer chains is complex and challenging to simulate.
• Polymorphism and crystal perfection are key characteristics in polymer self-assembly.

Purpose of the Study:

• To investigate the spontaneous crystallization of freely jointed polymers of hard spheres.
• To analyze the resulting polymorphs and crystal perfection using advanced simulation techniques.
• To elucidate the thermodynamic driving forces behind the observed phase transitions.

Main Methods:

• Employed an unprecedentedly long Monte Carlo (MC) simulation.
• Simulated a system of 54 polymer chains, each with 1000 monomers.
• Analyzed chain conformational characteristics, monomer spatial distribution, and accessible volume.

Main Results:

• Observed spontaneous crystallization from an amorphous state.
• Identified initial hexagonal closed packed (HCP) and random hexagonal close packed (rHCP) phases.
• The system ultimately formed a stable, highly perfect face-centered cubic (FCC) crystal.
• Phase transition driven by a favorable increase in translational entropy over conformational entropy loss.
• Average chain size remained constant, with polymers adopting ideal random walk statistics in the FCC crystal.

Conclusions:

• Freely jointed hard sphere polymers can achieve high perfection in FCC crystals.
• The crystallization is thermodynamically driven by entropy.
• Long polymer chains exhibit ideal random walk behavior in crystalline states, irrespective of local conformational constraints.