Self-assembly of various structures in colloidal systems with controlled interactions under confinement conditions

Abstract

Controlled self-assembly under spatial confinement plays a key role in the development of microfluidics and organ-on-a-chip platforms, yet the influence of tunable interactions on this process remains poorly understood. Here, we present a comprehensive analysis of how confinement height and dipole-dipole coupling govern phase selection in polarized colloidal systems.
Using superparamagnetic polystyrene microparticles in a tunable vertical magnetic field, alongside Langevin dynamics simulations incorporating Weeks-Chandler-Andersen and dipolar potentials, we mapped detailed phase diagrams. The results demonstrate a rich structural evolution depending on the dipole moment magnitude and the available space along the z-axis. Under strong confinement, the system forms close-packed hexagonal monolayers, while increased interactions induce elongated snake-like structures stabilized by dipolar alignment. Furthermore, we identified a unique "square liquid" phase, which combines liquid-like mobility with local square ordering of particles.
As channel height increases, the emergence of out-of-plane degrees of freedom triggers a competition between linear chain growth and branching. This suppresses long snakes, promoting the formation of dense triplet networks and driving a crossover from quasi-two-dimensional structures to genuinely three-dimensional multilayer configurations. The observed transition from linear chains to branched and layered motifs structurally mirrors complex biological microarchitectures, such as hepatocyte cords in liver tissue. Ultimately, these findings elucidate the physics of confined collective organization, providing a foundational framework for the programmable design of soft-matter architectures in biomimetic channels and tissue engineering.

Speaker

Kostantin P. Zhukov
Bauman Moscow State Technical University, Moscow, Russia
Russia

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