Dissipative self-assembly of colloidal suspensions

TL;DR

This paper investigates how paramagnetic colloid suspensions self-assemble into various dynamic structures under magnetic toggling, revealing six distinct regimes and the influence of confinement on anisotropic domain shapes.

Contribution

It introduces a dissipative self-assembly method for colloids, constructs a phase diagram of structural regimes, and models domain shapes with magnetostatic energy calculations.

Findings

Six characteristic structural regimes identified

Magnetostatic energy predicts anisotropic structures

Self-assembly driven by toggling magnetic fields

Abstract

Suspensions of paramagnetic colloids exhibit kinetic arrest in strong magnetic fields. Through a dissipative process of toggling the field on and off, suspensions self-assemble into dense and dynamic steady-state phases. Based on the domain elongation, alpha- and contour-shapes, and degree of phase separation, we construct a phase diagram using a k-means clustering analysis. We identify six characteristic structural regimes: a structureless phase, an arrested structure, sheets, ribbons, a spiky phase, and a transient fluid-fluid regime. We further report the distribution and alignment of domains and the generality of the results. We model self-assembled domain shapes using an equilibrium mean-field magnetostatic energy calculation, which predicts the surprising emergence of highly-anisotropic structures driven by the sample's confinement.