Prof. Roel Dullens (University of Oxford, UK)

Dynamics of Grain Boundary Loops in Two-Dimensional Colloidal Crystals
When Oct 24, 2016
from 02:00 PM to 03:00 PM
Where LR8
Contact Name
Contact Phone 01865-283446
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Many aspects of the dynamics of grain boundaries in polycrystalline metals and alloys remain unclear as direct observation of grain boundary migration at the atomic level is cumbersome with current techniques. In this respect, grain boundaries in colloidal crystals are convenient model systems since imaging their dynamics requires only simple optical microscopy and they can be manipulated using optical tweezers. In colloidal polycrystalline materials, grain boundaries form a network akin to that found in most metals but these systems remain very complex to study the details of grain boundary migration.    Here, we look at grain boundary dynamics in the simple case of an isolated circular grain boundary, called a grain boundary loop. In a colloidal crystal, we can create such loops on demand, using holographic optical tweezing. After creation, such grain boundary loops spontaneously shrink under the action of capillary forces. We find that complete shrinkage of the grain enclosed by the loop takes longer upon increasing the misorientation of the grain boundary. The rate of shrinkage also strongly depends on the initial radius of the loop. Importantly, we prove the existence of a transition between a regime of pure grain rotation and one dominated by shrinkage, which is specific to grain boundary loops. Finally we elucidate the shrinkage mechanism by directly visualising the dislocation reactions that enable the reduction of the grain boundary perimeter.