Time-dependent interactions for directed self-assembly of 2D colloidal crystals

Abstract

The assumption of time-independent interactions is fundamental to statistical physics. This work reexamines this paradigm by exploring the previously unstudied domain of many-particle systems with explicitly time-dependent interactions, implemented via external fields in colloidal systems. We demonstrate that periodic modulation of interactions on characteristic system timescales can drive the system into nonequilibrium states, unveiling new pathways for controlled self-assembly. Using molecular dynamics simulations of a two-dimensional colloidal system with interactions controlled by a conically rotating magnetic field, we identify specific time-dependent field regimes that promote rapid and efficient recrystallization from a polycrystalline to a single-domain structure. Genetic optimization revealed that these regimes, which involve switching between conical/vertical or elliptical field configurations, are robust across different initial states, system sizes, and densities, and remain effective under both Langevin and Brownian dynamics. In contrast, regimes with conventional static interactions proved significantly less effective or entirely incapable of recrystallization. Mechanism analysis shows that field switching induces anisotropy in the kinetic energy and displacement of defects depending on their crystallographic orientation, which drives the recrystallization process. Our results establish time-dependent interactions as a powerful tool for creating novel nonequilibrium regimes in soft matter, opening new possibilities for the design of advanced materials and controlled self-assembly.

Speaker

Alina R. Krasina
Bauman Moscow State Technical University
Russia

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