(61c) Assembly and Dynamics of Shape Anisotropic Colloidal Particles in Time-Varying Magnetic Fields

The expanding library of shape anisotropic colloidal particles is of much interest because of their potential to assemble into complex structures and guide the design of novel functional materials. Despite the availability of diverse shape anisotropic particles, experimental studies on their phase transition behavior under external stimuli remain limited. Here, we present a systematic experimental investigation of the role of shape anisotropy on the assembly of colloidal particles using external magnetic fields. We use a contact-lithography technique to fabricate plate-like non-magnetic colloidal particles with shapes ranging from circular discs to polygons with increasing vertices (n) from 3 ≤ n ≤ 6 and immerse them in a magnetic medium consisting of iron oxide nanoparticles. The application of an in-plane rotating magnetic field generates a tunable long-range attractive potential between colloidal particles that drives the phase transition from an initial disordered to assembled structures in a 2D plane comparable to the densest packing of the corresponding particle shape. We demonstrate that the kinetics of phase transitions are dependent on the strength of the applied magnetic field by measuring orientational order parameter of assembled structures. Additionally, our approach allows for reversible transitions between disordered and ordered colloidal structures, enabling the quantification of melting transition for various particle shapes. Our results provide insight into the spatiotemporal control over the assembly of shape anisotropic colloids, which can be extended to developing reconfigurable materials.