Spontaneous crystallization in athermal polymer packings

Area of Science:

• Polymer physics
• Materials science
• Computational chemistry

Background:

• Understanding the phase behavior of polymers is crucial for designing new materials.
• Athermal systems provide a simplified model to study fundamental packing and crystallization phenomena.
• The role of local structure in driving macroscopic phase transitions remains an active area of research.

Purpose of the Study:

• To investigate the spontaneous crystallization of athermal polymer packings through extensive simulations.
• To identify the critical conditions and resulting morphologies of polymer crystallization.
• To elucidate the microscopic origins and driving forces behind the observed phase transition.

Main Methods:

• Extensive molecular dynamics simulations of freely-jointed tangent hard-sphere polymer chains.
• Analysis of packing density, simulation duration, and resulting phase behavior.
• Characterization of local atomic environments using Voronoi polyhedra analysis.

Main Results:

• Spontaneous transition to a crystalline phase observed above a critical packing density and simulation time.
• Predominant formation of random hexagonal close-packed (RHCP) morphologies in polymer crystals.
• Voronoi cells around monomers become more spherical and symmetric during crystallization.
• Increased monomer translational entropy identified as the driving force for the phase transition.

Conclusions:

• Athermal polymer packings exhibit spontaneous crystallization into RHCP structures under specific conditions.
• The transition is entropically driven by the ordering of local monomer environments.
• Chain connectivity influences crystallization compared to hard-sphere monomers, highlighting polymer-specific effects.