Secrets of crystal growth unveiled
doi:10.1038/nindia.2013.14 Published online 29 January 2013
Researchers have provided new insights into the mobility and rearrangement of grain boundaries (GBs), the interface between two grains in specific polymer-derived colloidal crystals, by applying external force such as shear stress1. Such insights will be useful in directing grain growth, opening new avenues to fabricate desired commercial materials.
The motion of GBs is key to understanding grain growth and its stagnation in a broad class of polycrystalline materials, including metals, ceramics, colloidal crystals, and block copolymers. Although transmission electron microscopy (TEM) is used to measure grain growth, current techniques cannot quantify the dynamics of individual particles in grains and GBs.
To shed new light on the mobility of GBs and their roles in grain growth, the researchers tagged polymer-derived colloidal crystals with fluorescent molecules and then loaded these crystals in a home-made sample holder attached to a rheometer to apply shear stress on the colloidal crystals. Sophisticated imaging techniques were used to measure grain growth under shear stress by illuminating the sample with white light at an angle.
On applying shear stress, the mobility of GBs that were oriented parallel to shear increased, while GBs perpendicular to shear remained unchanged. The external shear stress also altered the motion of individual colloidal particles at GBs.
The study found that the shear-induced mobility of GBs led to directional grain growth. The researchers say that these results will be handy for materials fabrication strategies for atomic and block copolymeric polycrystals.
The authors of this work are from: Department of Physics, Indian Institute of Science, Chemistry and Physics of Materials Unit and International Centre for Materials Science Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India.
- Gokhale, S. et al. Directional grain growth from anisotropic kinetic roughening of grain boundaries in sheared colloidal crystals. P. Natl. Acad. Sci. USA 109, 20314-20319 (2012)| Article |