Flowing Precious Metals

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Science  15 Sep 2006:
Vol. 313, Issue 5793, pp. 1542
DOI: 10.1126/science.313.5793.1542b

With the exception of mercury, metals tend to require substantial heating before flowing as liquids; even alloys expressly designed for use as soldering fluxes generally melt well above room temperature. Warren et al. show that a particular ligand and counter-ion combination confers flowing properties to a range of precious metal nanoparticles ∼2 nm in diameter. Crystalline particles of platinum and gold, and predominantly amorphous palladium and rhodium particles, were prepared with N,N-dioctyl-N-(3-mercaptopropyl)-N-methyl ammonium capping ligands (bound to the metal through sulfur) by reduction of metal salts in tetrahydrofuran solution. Exchange of bromide counter-ions with sulfonates bearing long hydrophobic tails yielded a substance that, after thorough drying under vacuum, exhibited highly viscous liquid-like flow at room temperature; a 50-mg droplet moved at a rate of just over 2 cm/hour down an inclined glass plane. The authors envision that these flowing nanoparticles may offer convenient routes to self-assembled materials, as well as applications in heat-transfer media. — MSL

J. Am. Chem. Soc. 128, 10.1021/ja064469r (2006).

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