This talk will present strategies for magnetic field driven assembly and manipulation of dynamic and active structures from colloidal particles. Achieving reconfigurability requires designing means of flexibly connecting the particles and programming their response. The flexible binding can be achieved by capillary bridging or by magnetic attraction. We will first describe the assembly of ultraflexible fibrils from magnetically responsive nanoparticles bound by nanocapillarity. The nanocapillary binding leads to easy particle rolling and sliding. The soft, "snappable," capillary interactions enable the making of magnetically self-repairing gel networks, novel 3D-printing inks, and precise clusters from Janus particles. Next, we will discuss how magnetically responsive metallo-dielectric Janus microcubes can be assembled hierarchically into dynamically reconfiguring microclusters and chains. These assemblies can store energy through magnetic polarization of the metallic facets and release it on-demand by microscale reconfiguration. The reconfiguration is directed by the conformational shape restrictions of the neighboring microcubes. Thus, the pattern of folding and shape changes of the assemblies can be encoded in the sequence of the cube orientation. Such structures can be directionally moved, steered, and maneuvered by external magnetic fields. We will provide examples of assemblies of specific sequences that can be actuated to perform microscale operations such as capturing and transporting live cells, acting as prototypes of microbots, micromixers and other active microstructures. Such reconfigurable clusters can also be designed to be self-motile in media with non-Newtonian rheology when actuated with an asymmetric magnetic signal. We will analyze the dynamics of these active structures under different propulsion conditions on the basis of a “coupled scallop” model and will suggest means of controlling the motility in in different directions by means of both particle sequence and signal shape.

Engineering of shape-changing and motile colloidal assemblies: Magnetically reconfigurable clusters and self-propelling microbots

254th National Meeting (2017)

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