Phase diagram and aggregation dynamics of a monolayer of paramagnetic colloids

Abstract

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 $\theta$ of the rotating magnetic field. For a purely in-plane field, $\theta =90^{\circ }$, interactions are attractive and the experimental results agree well with both equilibrium and out-of-equilibrium predictions based on a two-body interaction model. For tilt angles $50^{\circ }\lesssim \theta \lesssim 55^{\circ }$, 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 time-dependent cluster size distribution.

12 pages, 8 figures

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Cited by in corpus (2)

• The role of attraction in the phase diagrams and melting scenarios of generalized 2D Lennard-Jones systems
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