Dissipative self-assembly of magnetic colloids

Suspensions of paramagnetic colloids form arrested gel-like structures in the presence of sufficiently powerful magnetic fields. Through a dissipative process of toggling the field on and off, suspensions can be directed to 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 by a k-means clustering analysis composed of six steady-state structural phases: an unstructured phase, an arrested structure, sheets, ribbons, a spiky phase, and a fluid-fluid phase. We further report the spacing and alignment of domains and the generality of the results. We model domain shapes using a mean-field calculation of the time-averaged magnestatic energy which predicts the surprising emergence of highly- anisotropic structures in confinement.