Entropy-Driven Heterogeneous Crystallization of Hard-Sphere Chains under Unidimensional Confinement

Area of Science:

• Polymer physics
• Materials science
• Computational chemistry

Background:

• Understanding polymer crystallization is crucial for materials design.
• Confinement effects significantly alter phase behavior.
• Heterogeneous crystallization in confined systems remains an active research area.

Purpose of the Study:

• To investigate the heterogeneous crystallization of linear polymer chains under one-dimensional confinement.
• To analyze the influence of chain length and packing density on crystal structure.
• To differentiate between bulk and surface crystallization phenomena.

Main Methods:

• Monte Carlo simulations were employed to model the system.
• One-dimensional confinement was achieved using parallel, impenetrable walls.
• The Characteristic Crystallographic Element (CCE) norm descriptor quantified local structure.

Main Results:

• A phase transition was observed above a critical volume fraction, initiating near the walls.
• Crystal morphologies included alternating hexagonal close-packed (HCP) or face-centered cubic (FCC) layers perpendicular to walls.
• Crystal perfection increased with concentration, with surface crystallites showing triangular, square, or mixed morphologies.

Conclusions:

• Confinement drives heterogeneous crystallization, starting at surfaces.
• Crystal layer perfection is density-dependent and comparable between bulk and surface.
• The competition between crystal growth and fivefold symmetry sites is observed, similar to unconstrained systems.