Energy-Entropy Transition in Defect Distribution of Melting Colloidal Monolayers with Tunable Interactions

Abstract

The melting of two-dimensional systems, such as colloidal monolayers with tunable interactions, is fundamentally governed by the thermodynamics of lattice defects. While the role of defect concentration is well-established, the evolution of their spatial organization remains less explored. Here, we employ molecular dynamics simulations that model colloidal particles with tunable interactions, comparing systems governed by purely pairwise potentials with those incorporating attractive three-body forces.
Our results identify two distinct regimes for the defect subsystem. At low temperatures, an energy-dominated regime prevails, where the system minimizes its free energy by expelling defects to the crystallite boundaries. Upon heating, this ordered state gives way to an entropy-dominated regime, where configurational entropy favors the delocalization of defects throughout the crystal bulk.
We visualize this transition by comparing the measured average defect-to-surface distance against a theoretical baseline for a random distribution. Irrespective of the interaction potential, the system is observed to evolve towards this baseline, indicating the onset of the entropy-dominated regime. The defect distribution then conforms to this random state without systematically exceeding it, suggesting it represents a terminal configuration for the defect subsystem. This reframes 2D melting as an intrinsic order-disorder transition within the defect subsystem itself.

Speaker

Bystrov Daniil Aleksandrovich
Bauman Moscow State Technical University, 2nd Baumanskaya street 5, Moscow, 105005, Russia
Russia

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