Shape-dependent disassembly of polygonal microparticles in two dimensions. | CU Experts

Understanding how particle shape governs the assembly and relaxation of colloidal clusters is critical for designing reconfigurable materials. Here, we experimentally investigate the assembly and disassembly dynamics of shape-anisotropic colloidal microparticles confined to two dimensions using a rotating magnetic field. Plate-like, non-magnetic regular polygonal particles (3-6 vertices), each inscribed within a circle of fixed radius, are fabricated via photolithography and dispersed in a magnetic nanoparticle medium, where an in-plane rotating field induces tunable long-range attractions that drive assembly into ordered clusters. Removal of the field enables controlled disassembly governed by thermal diffusion. We show that disassembly kinetics depend on particle shape, with particles having fewer vertices disordering more rapidly than those with more vertices. By quantifying single-particle rotational dynamics, we link the particle shape and relaxation behavior, where particles with fewer vertices exhibit higher effective rotational diffusivity, while higher-vertex polygons experience constrained motion. These results show that disassembly is governed by a combination of local constraint networks and shape-dependent rotational drag, providing design principles for reconfigurable colloidal materials.

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