Microbots and Colloidal Origami: Dynamically Interacting and Self-Reconfiguring Assemblies of Metallo-Dielectric Janus Microcubes

A new class of dynamically and reversibly reconfigurable active matter made by magnetic assembly and actuation of metallo-dielectric microcubes will be presented. We have shown earlier how metallo-dielectric Janus/patchy spheres and microcubes acquire complex polarization patterns in electrical and magnetic fields, leading to multidirectional interactions and assembly. Now we will describe how magnetically responsive Janus microcubes can be assembled hierarchically into dynamically reconfiguring microclusters and microchains. The residual polarization of the metal-coated facets leads to directional dipole-dipole and field-dipole interactions and reconfiguration of the neighboring cubic particles, which is directed by the conformational restrictions. We seek to establish how the external field energy is converted by residual interactions and conformational restrictions into programmed cluster and chain dynamics. The sequence of cis- and trans-conformations of the Janus cubes determines how the chain will respond and fold after the external field is turned off. Depending upon this orientational sequence, the microchains can attain various equilibrium and non-equilibrium conformations by self-folding and wrapping. The magnetically controlled folding and unfolding can be designed to be reversible and can be used to fabricate active structures. We show how pre-assembled Janus microcube clusters can be reversibly actuated, oriented and spatially transported by changing the magnetic field parameters. They can also be designed to be self-motile in media with specific rheological properties. These motile clusters can serve as early prototypes of microbots capable of grabbing and transporting target micro-objects.