Inducing point defects in 3D colloidal crystals

Crystal defects are imperfections that can crucially influence the properties of crystalline materials. Colloidal crystals serve as useful model systems to study defect phenomena due to their similarities with atomic crystal systems. Although several types of defects have been studied in colloidal crystals, the lack of experimental control over point defect formation provides a challenge for studying the diffusion and interaction phenomena of these defects. We developed a model system in which point defect formation in 3D colloidal crystals can be controlled in-situ. This system consists of poly(N-isopropyl acrylamide) microgels embedded in a crystal of non-responsive poly(2,2,2-trifluoroethyl methacrylate) colloids. Heating this mixed particle system results in shrinking of the embedded microgels, and subsequently induces the formation of vacancy-interstitial pairs. Using temperature-controlled confocal microscopy experiments we study the formation of the point defects in 3D colloidal crystals, and are able to visualize the local lattice strain after interstitial defect formation. The experimental model system presented here provides the unique opportunity to shed new light on the interplay between point defects, the mechanisms of their diffusion, and collective dynamics.