Dynamic Materials from Colloidal Crystals: Active Matter Coupled to Crystalline Defects

When many thousands or millions of designed components are combined a new class of material is formed, generally known as a metamaterial. When the subcomponents are capable of exerting individual forces, sensing, or communicating a truly exotic material with potentially life-like qualities is produced. The design and control of such a material for engineering purposes is a daunting task, especially when the size of each subcomponent is desired to be very small (i.e. sub-micron); In such a case the sensing, actuation, and communication abilities of each subunit are severely restricted.

We present a strategy for controlling the macroscopic properties of artificial crystalline materials by taking control over the dynamics of dislocation lattice defects. In this scheme, the majority of the material is passive, with a small fraction of active components capable of exerting individual forces. By coupling the active components to lattice defects, their range of influence can be extended far enough to control macroscopic properties.

Using this concept, we demonstrate (via simulation) how bulk material properties such as resistance to plastic deformation can be controlled, as well as how directed dislocation motion can be used for actuation and re-shaping of crystalline metamaterials. We show how the strain field of mobile active interstitials within the material can be tuned via Monte Carlo optimization for maximized coupling, as well as how forces generated from an embedded cluster of active material can be designed to create dislocation pairs which can be used for bulk material reconfiguration.

By only using a small fraction of active components, the planning, control, and component complexity requirements necessary to design the collective behavior of the material are relaxed, paving the way for experimental realization of adaptive active metamaterials at the colloidal scale.