Fabrication of Highly Flexible Copper Nanowires in Dual Surfactant Hydrothermal Process

Highly flexible Cu nanowires were successfully synthesized by a dual-surfactant hydrothermal process using oleylamine and oleic acid. The ultra-long Cu nanowires have a mean diameter as low as 82.3 nm and lengths greater than 300 μm. It was found that reaction time and oleylamine concentration significantly influenced the morphology and phase composition of the Cu products. At a shorter reaction time (about 4 hours), pentagonal bipyramidal CU₂O particles were precipitated together with the Cu nanowires. A longer reaction time of 12 hours resulted in smooth and purely metallic Cu nanowires. It is possible that CU₂O served as an intermediate phase to control the activity of free CU²⁺ ions in the solution. On the other hand, a higher oleylamine concentration generally produced longer Cu nanowires. Cu nanowires conducting electrode with a sheet resistance of about 157.0 Ω/□ were fabricated. However, the optical transmittance of the electrode at 550 nm was very low (<20%) because of the agglomeration of the Cu nanowires. The addition of a small quantity of Ag nanowires in the Cu nanowire ink markedly improved the appearance and electrical properties of the resulting electrode.