(455e) Making Complex Materials out of Simple Particles – Strategies for Particle Assembly, Binding and Manipulation in Magnetic Fields and in Multiphasic Systems

The engineered assembly of colloidal microparticles can provide simple and efficient means for making sophisticated “active” structures and materials. The key to making these structures is the engineering of directional interactions and of flexible inter-particle bonds. We will discuss how magnetic fields can be used to make novel classes of flexible, responsive and dynamically reconfigurable gel networks, shape-changing microbots, and inks for 3D printing. In the first part of the talk, we will discuss how the magnetic polarization patterns on metallodielectric microcubes lead to multidirectional interactions and assembly of reconfigurable microclusters. These sequence-encoded clusters can be reversibly actuated by magnetic fields and can be designed to be self-motile in non-Newtonian media. In the second part of the talk we will describe two new types of multiphasic capillary gels made from particles bound by liquid bridges. The first gel system is composed of filaments from magnetically responsive iron oxide nanoparticles suspended in water-oil systems. The nanocapillary binding results in ultra-high filament flexibility. The second multiphasic system is a new class of 3D printing inks consisting of PDMS microbeads, liquid PDMS and water. Owing to the capillary binding, such Homocomposite Thixotropic Pastes (HTPs) can be extruded and shaped on a 3D printer. The curing of the liquid bridges in the HTPs results in remarkably elastic and flexible porous silicone material. The HTP 3D printing method makes possible the fabrication of soft architectures that reconfigure in magnetic fields and could find a broad range of applications, such as making 2D auxetic materials, soft actuators, soft robots and bioscaffolds.