Rotating magnetic fields control colloidal self-assembly and phase transitions

TitleRotating magnetic fields control colloidal self-assembly and phase transitions
Publication TypeJournal Article
Year of Publication2016
AuthorsPham, AT, Zhuang, Y, Detwiler, P, Socolar, JES, Charbonneau, P, Yellen, BB
Date Published12/2016

We have developed a tunable colloidal system and a corresponding simulation model for studying the phase behavior of particles assembling under the influence of long-range magnetic interactions. A monolayer of paramagnetic particles is subjected to a spatially uniform magnetic field with a static perpendicular component and rapidly rotating in-plane component. The sign and strength of the interactions vary with the tilt angle θ of the rotating magnetic field. For a purely in-plane field, θ = 90◦ , interactions are attractive and the experimental results agree well with both equilibrium and outof-equilibrium predictions based on a two-body interaction model. For tilt angles 50◦ . θ . 55◦ , the two-body interaction gives a short-range attractive and long-range repulsive (SALR) interaction, which predicts the formation of equilibrium microphases. In experiments, however, a different type of assembly is observed. Inclusion of three-body (and higher-order) terms in the model does not resolve the discrepancy. We thus further characterize the anomalous behavior by measuring the timedependent cluster size distribution.