(35h) Adaptive Mechanical Properties of Colloidal Crystals Via Active Interstitials

Future sub-millimeter robotic devices will require materials with dynamic mechanical properties, similar in functionality to the unicellular cytoskeleton. Here we explore how the mechanical properties of a crystal composed of colloidal particles can be modified through the addition of small fractions of active, anisotropic interstitials. Such interstitial particles can pin the migration of crystal defects, thereby increasing resistance to deformation and shape change. Through computer simulation we show how swarms of self-propelled particles can dynamically reduce material deformation. When optimized, such swarms search the interior of the crystal for sites to inhabit near defects that have a large impact on the plastic deformation properties of the solid. We find that there is an exploitation/exploration tradeoff centered around the rotational freedom of the active interstitials. By understanding the mechanisms of interstitial-host interaction, we show that number concentrations as low as 100 interstitials per million host particles can cause dramatic changes in material deformability. These results propose a framework for colloid-based metamaterials with dynamic deformation behavior.