PerspectiveMaterials Science

Melting Colloidal Crystals from the Inside Out

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Science  05 Oct 2012:
Vol. 338, Issue 6103, pp. 55-56
DOI: 10.1126/science.1228952

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Consider an ice cube melting in a glass of water. Ice cubes and any other solid objects almost always melt from their outer surface inward, and this scenario is well understood by physicists. What is less common, less well understood, but more intriguing is the case when a solid melts from inside outward (see the figure, panel A). Experimentally, this might be achieved by focusing an intense laser pulse inside a solid sample to locally superheat it. However, in such experiments, the sample melts extremely quickly, and it is difficult to determine exactly how the melting proceeds. On page 87 of this issue, Wang et al. (1) report the creative use of colloids as a model system to study the internal melting of samples in slow motion and with high magnification. They find that large agitations are the main driver of sample melting, rather than the formation of crystalline defects, contradicting some theoretical expectations.