Dislocation reactions during granule rotation

Grain boundaries are composed of a sequence of dislocations, which diffuse and mutually interact. When one crystal grain is enclosed within another crystal, the resulting grain boundary loop shrinks as the enclosed grain dissolves over time to minimize free energy. In our colloidal crystal experiments, we observe a new mechanism for grain dissolution in which hexagonal particle clusters, or "granules", rotate to switch from one crystal orientation to another. The role of dislocations during granule rotation is not well understood, and is complicated by the presence of rapidly evolving grain boundaries. The conventional view of grain dissolution predicts that dislocations will glide until they meet and interact through dislocation reactions or dissociations. However our preliminary results indicate a more complicated behavior, in which the dislocation reactions are influenced by local variations in misorientation angle caused by granule rotation. These observations suggest that the existing framework for understanding grain boundary motion in terms of dislocations may be insufficient for modeling granule rotation.