A facile way to prepare tiny Cu nanoparticles from micro-emulsion micelles of Cu(II) di-n-dodecylbenzene sulfonate

Cu(II) di-n-dodecylbenzene sulfonates prepared from neutralization between CuO and n-dodecylbenzene sulfonic acid self-assemble into micro-micelles in water and reduced to CuNPs by sodium boron hydride. Energy dispersive x-ray spectra prove that CuNPs are covered by the unreactive HDBS and n-dodecylbenzene sulfonate (DBS-) and prevent the aggregation of CuNPs, keeping their sizes at tiny nanoscales and resulting in the λmax at 550–600 nm in the UV-Vis spectra. Without antioxidants or capping agents, the as-prepared CuNPs are well protected from oxidation by surfactants as confirmed by x-ray diffraction patterns. The micelle shapes of surfactant DBS- control the precipitated morphologies of the CuNPs. According to SEM and TEM micrographs, the average size of the CuNPs is at around 2–3 nm with a low melting point at ca. 140 °C measured by DSC and free from oxidation in the air below 140–150 °C by TGA thermograms. The surfactant-covered CuNPs are easily dispersed into a conducting ink and their electrical resistance drops sharply over 136 °C, attributable to the formation of a conducting network derived from the fusion of CuNPs.