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Science , Vol 309, Issue 5738, 1207-1210, 19 August 2005
[DOI: 10.1126/science.1112399]
Originally published in Science Express on 30 June 2005
Research Articles
Premelting at Defects Within Bulk Colloidal Crystals
A. M. Alsayed, 1 M. F. Islam, 1 J. Zhang, 1 P. J. Collings, 1 ,2 A. G. Yodh 1*Premelting is the localized loss of crystalline order at surfaces and defects at temperatures below the bulk melting transition. It can be thought of as the nucleation of the melting process. Premelting has been observed at the surfaces of crystals but not within. We report observations of premelting at grain boundaries and dislocations within bulk colloidal crystals using real-time video microscopy. The crystals are equilibrium close-packed, three-dimensional colloidal structures made from thermally responsive microgel spheres. Particle tracking reveals increased disorder in crystalline regions bordering defects, the amount of which depends on the type of defect, distance from the defect, and particle volume fraction. Our observations suggest that interfacial free energy is the crucial parameter for premelting in colloidal and atomic-scale crystals.
1 Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104–6396, USA.
2 Department of Physics and Astronomy, Swarthmore College, Swarthmore, PA 19081–1397, USA.
* To whom correspondence should be addressed. E-mail: yodh@physics.upenn.edu
Yodh Group web site: http://www.physics.upenn.edu/yodhlab/