Copper nanoparticles, due to their interesting properties, low cost preparation and many potential applications in catalysis, cooling fluid or conductive inks, have attracted a lot of interest in recent years. In this study, copper nanoparticles were synthesized through the chemical reduction of copper sulfate with sodium borohydride in water without inert gas protection. In our synthesis route, ascorbic acid (natural vitamin C) was employed as a protective agent to prevent the nascent Cu nanoparticles from oxidation during the synthesis process and in storage. Polyethylene glycol (PEG) was added and worked both as a size controller and as a capping agent. Cu nanoparticles were characterized by Fourier transform infrared (FT-IR) spectroscopy to investigate the coordination between Cu nanoparticles and PEG. Transmission electron microscopy (TEM) and UV–vis spectrometry contributed to the analysis of size and optical properties of the nanoparticles, respectively. The average crystal sizes of the particles at room temperature were less than 10 nm. It was observed that the surface plasmon resonance phenomenon can be controlled during synthesis by varying the reaction time, pH, and relative ratio of copper sulfate to the surfactant. The surface plasmon resonance peak shifts from 561 to 572 nm, while the apparent color changes from red to black, which is partly related to the change in particle size. Upon oxidation, the color of the solution changes from red to violet and ultimately a blue solution appears.

Inkjet printing is an advanced technique which reliably reproduces text, images and photos on paper and some other substrates by desktop printers and is now used in the field of materials deposition. This interest in maskless materials deposition is coupled with the development of microfabrication techniques for the realization of circuits or patterns on flexible substrates for which printing techniques are of primary interest. This paper is a review of some results obtained in inkjet printing technology to develop microfabrication techniques at Laboratory for Nanotechnology (LNT). Ink development, in particular conductive ink, study of printed patterns, as well as application of these to the realization of radio-frequency identification (RFID) tags on flexible substrates, are presented.

In this paper we present silver nanoparticles ink synthesis targeting conductive patterns for micro fabricated devices by inkjet printing technology. The well dispersed nanoparticles ink was composed of silver colloid with an average particle diameter less than 10 nm. These nanoparticles were protected by a capping layer of poly(N-vinylpyrrolidone) (PVP) even at silver concentration of 20 wt%. Stable aqueous inks were formulated by using a combination of solvent and co-solvents and under vigorous stirring. Various factors affecting the adhesion between the ink and the substrate were investigated, such as solvent and co-solvent content. The ink containing 20 wt% silver has a viscosity of about 9.5 cP and a surface tension of 32 to 36 mN m −1 at room temperature, meeting inkjet printer requirements. The ink stored under ambient conditions was stable against aggregation for more than one month. Silver nanoparticles patterns have been successfully printed on various substrates.

In this study, silver nanoparticles were synthesized from silver nitrate via a polyol method in ambient atmosphere. In our synthesis route, polyvinylpyrrolidone (PVP) is used as both size controller and capping agent, ethylene glycol acts both as solvent and reducing agent. The obtained silver nanoparticles were characterized by ultraviolet-visible spectrophotometry which indicated the formation of nanoparticles. Investigation of Fourier transform infrared spectroscopy clearly demonstrated the coordination between silver nanoparticles and PVP. Transmission electron microscopy (TEM) contributed to the particle size analysis. The surface plasmon resonance peak in absorption spectra of silver colloidal solution showed absorption from 406 to 409 nm. The average size of the resulting silver nanoparticles was below 10 nm with a dependency on the PVP concentration.

A chemical reduction method for preparing colloidal copper nanoparticles in water and ethylene glycol (EG) is reported. The obtained copper nanoparticles were characterized by powder x-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible spectrophotometry (UV-vis). Surface plasmon resonance peaks immediately after the synthesis appeared at 579 and 551 nm for the colloidal copper in water and EG, respectively. The stability of colloidal copper in EG was longer than that in water. The color of solution in water changed from light-red to black and the nanoparticles mostly precipitated after 22 days, which is attributed to the oxidation of copper nanoparticles in copper oxide (I), as was confirmed by optical absorption measurements. In EG, copper nanoparticles were red and stable even after 2 months. Ascorbic acid plays a role as antioxidant for colloidal copper, due to its ability to scavenge free radicals and reactive oxygen molecules. Polyvinyl pyrrolidone works both as size controller and polymeric capping agent because it hinders the nuclei from aggregation through the polar groups, which strongly absorb the copper particles on the surface with coordination bonds.