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Posted: Nov 27, 2012
Researchers control the arrangement of nanoparticles via temperature
(Nanowerk News) It is merely the arrangement of the carbon that makes it look so different. Highly ordered carbon makes a hard gemstone, incoherent and powdery carbon is more appropriate for a barbecue or writing letters. High pressures and temperatures – natural or artificial – can change the properties of carbon, and graphite becomes diamond. Researchers at the INM – Leibniz Institute for New Materials were surprised to observed similar changes when monitoring nanoparticles: only at elevated temperatures did very small gold nanoparticles arrange into well-ordered crystals. The results were published in the renowned journal Physical Review Letters ("Switching Between Crystallization and Amorphous Agglomeration of Alkyl Thiol-Coated Gold Nanoparticles").
"The properties of a material - electrical and thermal conductivity, optical transparency, mechanical hardness - depend on its internal structure. If we can control the arrangement of nanoparticles in a material, we should be able to change the properties of the material“, explains Tobias Kraus, Head of the Junior Research Group Structure Formation. The first step towards a modular design system for materials has been taken.
The material scientists from Saarbruecken achieved structural control for gold nanoparticles that are about a billion times smaller than a man: "It was known that such nanoparticles can spontaneously arrange into crystals. But we were really surprised when they only formed crystals when they were hot", says Kraus.
The gold nanoparticles that they used were covered with a thin, organic shell.
"At low temperatures, these shells are hard," suggests the Ph.D. student Philip Born, who is working with the nanoparticles. “Thus, the shells interdigitate, causing amorphous lumps to form. At higher temperatures, the shells melt and "lubricate" the nanoparticles: Suddenly, we obtain well-ordered crystals", says Born.
In the future, the researchers want to go beyond gold nanoparticles. "If we can also apply this principle to nanoparticles that have other cores and shells, we would have a modular design principle for particle-based materials", says Kraus.
Source: INM - Leibniz-Institut für Neue Materialien