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Vitrification, the formation of glass, requires the presence of disorder to frustrate crystallization. This can be achieved by mixing two sizes of particles in a fluid, and then cooling the fluid very rapidly to prevent phase separation as the glass ages. The interplay between aging, crystallization, and vitrification are explored in multiple colloidal experiments. Bidisperse colloidal suspensions of temperature-sensitive microgel spheres were quenched from liquid to glass states by a rapid temperature drop, and then the glass was permitted to age [1]. Irreversible rearrangements, events that dramatically change a particle's local environment, were observed to be closely related to dynamic heterogeneity. The slowing dynamics of aging were found to be governed by growing correlated domains of particles associated with these irreversible rearrangements. Additionally, short-range order developed during aging. This lead to an exploration of the role of frustration and quenched disorder in driving the transformation of a crystal into a glass [2]. The amount of frustration is varied via the number fraction of smaller particles. The crystal-glass transition bears structural signatures similar to those of the crystal-fluid transition: at the transition point, the persistence of orientational order decreases sharply from quasilong-range to short-range, and the orientational order susceptibility exhibits a maximum. The crystal-glass transition also features a sharp variation in particle dynamics: at the transition point, dynamic heterogeneity grows rapidly, and a dynamic correlation length scale increases abruptly.
[1]"Irreversible Rearrangements, Correlated Domains, and Local Structure in Aging Glasses," Peter Yunker, Zexin Zhang, Kevin B. Aptowicz, and A.G. Yodh, Physical Review Letters, 103, 115701 (2009). [2]"Observation of the Disorder Induced Crystal-to-Glass Transition," Peter Yunker, Zexin Zhang, and A.G. Yodh, Physical Review Letters, 104, 015701 (2010). We acknowledge the financial support of the National Science Foundation through DMR-080488 (A. G.Y.), the PENN MRSEC DMR-0520020, and NASA #NNX08AO0G. |
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