Here, they saw that gas and solid phases can coexist, resulting in polycrystalline structures that include particle-free regions. As recently shown in a previous study, this type of system is well suited for visualizing phase transitions characteristic of atomic systems. In experiments, the researchers induced colloids of paramagnetic particles to form 2D polycrystalline structures by spinning them with magnetic fields. But with our rotating magnetic field, the grain boundaries are dynamic and we can watch their motion.” “What sets our study apart is that in the majority of colloidal crystal studies, the grain boundaries form and remain stationary,” Lobmeyer said. Even though colloidal crystals have been used as model systems to see boundaries move, controlling their phase transitions has been challenging. Under applied stress, grain boundaries can form, reconfigure or even disappear entirely to accommodate new conditions. The organization of these polycrystalline aggregates govern such properties as conductivity and strength. But at the molecular scale, these materials are polycrystalline, separated by defects known as grain boundaries.
To the naked eye, common metals, ceramics and semiconductors appear uniform and solid. The technique reported in Science Advances could help engineers design new and improved materials. Brown School of Engineering, and graduate student and lead author Dana Lobmeyer, interfacial shear at the crystal-void boundary can indeed drive how microstructures evolve. That the boundaries can change so readily was not entirely a surprise to the researchers, who used spinning arrays of magnetic particles to view what they suspect happens at the interface between misaligned crystal domains.Īccording to Sibani Lisa Biswal, a professor of chemical and biomolecular engineering at Rice’s George R. HOUSTON – (June 6, 2022) – Rice University engineers who mimic atom-scale processes to make them big enough to see have modeled how shear influences grain boundaries in polycrystalline materials.