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Volume 181, 2015
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Nanocrystal superlattices that exhibit improved order on heating: an example of inverse melting?

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Abstract

Grazing incidence small angle X-ray scattering (GISAXS) measurements reveal that superlattices of 1.7 nm diameter, gold (Au) nanocrystals capped with octadecanethiol become significantly more ordered when heated to moderate temperatures (50–60 °C). This enhancement in order is reversible and the superlattice returns to its initially disordered structure when cooled back to room temperature. Disorder–order transition temperatures were estimated from the GISAXS data using the Hansen–Verlet criterion. Differential scanning calorimetry (DSC) measurements of the superlattices exhibited exotherms (associated with disordering during cooling) and endotherms (associated with ordering during heating) near the transition temperatures. The superlattice transition temperatures also correspond approximately to the melting and solidification points of octadecanethiol. Therefore, it appears that a change in capping ligand packing that occurs upon ligand melting underlies the structural transition of the superlattices. We liken the heat-induced ordering of the superlattices to an inverse melting transition.

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Submitted
13 Jan 2015
Accepted
20 Jan 2015
First published
20 Jan 2015

Faraday Discuss., 2015,181, 181-192
Article type
Paper
Author version available

Nanocrystal superlattices that exhibit improved order on heating: an example of inverse melting?

Y. Yu, A. Jain, A. Guillaussier, V. R. Voggu, T. M. Truskett, Detlef-M. Smilgies and B. A. Korgel, Faraday Discuss., 2015, 181, 181
DOI: 10.1039/C5FD00006H

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