PerspectiveMaterials Science

Unusual Thermoelastic Properties of Methanol Monohydrate

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Science  11 Feb 2011:
Vol. 331, Issue 6018, pp. 687-688
DOI: 10.1126/science.1201564

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When a material is heated, we expect it to expand, and when squeezed on all sides by hydrostatic pressure, we expect it to shrink, but materials or structures can respond in unexpected ways. Some may exhibit negative thermal expansion (NTE)—shrinking when heated (18)—or negative compressibility (NC) (813)—expanding when subjected to a positive hydrostatic pressure—and some may exhibit both properties. For crystalline materials, the response can be anisotropic—observed along only some directions in a crystal (see the figure), and may only be observed in particular ranges of temperatures or pressures. On page 742 in this issue, Fortes et al. (8) report such anomalous properties from an experimental investigation on methanol monohydrate, a simple molecular crystal of a deuterated 1:1 compound of methanol and water. Such materials, used singly or in combination with conventional materials, can have useful mechanical and optical properties.