Interstitial Particle Design for Active Colloidal Microstructures*

Defect microstructures in colloidal crystals can be viewed as complex localized motifs, distinct from the environments present throughout the bulk of the crystalline phase. These motifs are persistent sites which interstitial particles can adsorb onto and be trapped by. The degree to which interstitial particles are bound to the vicinity of defects can be explored as a function of particle geometry. We present here a method to maximize the strength of the preferential interaction that a rod-like interstitial experiences with defect microstructures that include edge dislocations. We show that for sufficiently strongly bound interstitials, microstructural migration can be induced by applying forces to the designed particle, making it active. This approach opens up many possibilities for dynamically manipulating the microstructure of colloidal crystals, with applications in shape changing colloidal assemblies. Furthermore, the line-like nature of dislocations permits widely separated interstitials to be connected, correlating their transport properties in a manner not typically possible with local particle interactions.