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Abstract:
A team of scientists from National University of Singapore has revealed the use of food chemistry-Maillard reaction to synthesize cheap and abundant copper nanowires for large scale transparent conductor.

Aromatic food chemistry to the making of copper nanowires

Singapore | Posted on November 24th, 2014

The food chemistry-Maillard reaction is responsible for many colors and flavors in foods  roasting of coffee, baking of bread and sizzling of meat. Scientists from National University of Singapore, Ghim Wei Ho and her team have made use of this ingenious food chemistry to ‘cook' their copper nanowires. Naturally, a lingering chocolate-like aroma was detected during the copper nanowires synthesis.

Metallic nanowires especially cheap and abundant copper nanowires have huge potential applications in miniaturized interconnects, sensors and transparent conductors featuring solar cells, touch screens and LED display. Traditionally, indium tin oxide (ITO) is the most widely used transparent conductor in today's consumer technology. However, alternatives are being sought due to the high cost and finite supply of indium. Films made from copper nanowires are promising candidates, exhibiting high conductivity and optical transparency in addition to being flexible.

Copper nanowires are typically synthesized by the reduction of Cu2+ in solution to its metal form using hydrazine and ethylenediamine, both of which are notoriously hazardous and toxic. Kevin Moe, the main researcher has uncovered a green approach that formulates copper atoms in water to form untangled metallic state nanowires. The thin and optimized length nanowires can then be transformed into smooth transparent, conductive films easily and quickly virtually onto any substrates  glass, plastic or even super hydrophobic lotus leaf.

The Maillard reaction between amino acids and reducing sugar occurs at approximately 140-165°C. By varying the type and concentration of reducing sugar and amine in the presence of Cu2+, the team has been able to synthesize copper nanowires with a tuneable aspect ratio via a green route for the first time. Through the addition of glycine, the copper nanowires length could be systematically tuned from several millimeters down to hundreds of micron. Such capability should not be underestimated as it serves to prevent the nanowires from getting irreversibly entangled, allowing excellent nanowire dispersions without the need for surfactants. The concomitant increase in nanowire's diameter to ~150 nm allows improved sheet resistances without compromising optical transparencies. The well-dispersed copper nanowires could be coated uniformly regardless of flat or curve geometries and wetting or non-wetting surfaces in every practical sense.

The findings have been reported in the Green Chemistry ("Facile control of copper nanowire dimensions via the Maillard reaction: using food chemistry for fabricating large-scale transparent flexible conductors").

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Contacts:
Ghim Wei Ho
Phone: 65-65168121

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