Phase diagram and aggregation dynamics of a monolayer of paramagnetic colloids


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.







Joshua Socolar

Professor of Physics

Prof. Socolar is interested in collective behavior in condensed matter and dynamical systems. His current research interests include:

  • Limit-periodic structures, quasicrystals, packing problems, and tiling theory;
  • Self-assembly and phases of designed colloidal particles;
  • Shear jamming and stick-slip behavior in dry granular materials;
  • Organization and dynamics of complex networks;
  • Topological elasticity of mechanical lattices.

Patrick Charbonneau

Professor of Chemistry

Professor Charbonneau studies soft matter. His work combines theory and simulation to understand the glass problem, protein crystallization, microphase formation, and colloidal assembly in external fields.

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