At present there is no metallic ink that enables formation of conductive patterns at room temperature by a single printing step. Printing conductive features by metallic nanoparticle-based inks must be followed by sintering while heating to elevated temperatures, thus preventing their utilization on most plastic substrates used in plastic electronics. In this report we present a new silver nanoparticle-based conductive ink, having a built-in sintering mechanism, which is triggered during drying of the printed pattern. The nanoparticles that are stabilized by a polymer undergo self-sintering spontaneously, due to the presence of a destabilizing agent, which comes into action only during drying of the printed pattern. The destabilizing-agent, which contains Cl- ions, causes detachment of the anchoring groups' of the stabilizer from the nanoparticles surface and thus enables their coalescence and sintering. It was found that the new metallic ink leads to very high conductivities, by a single printing step: up to 41% of the conductivity of bulk silver was achieved, the highest reported conductivity of a printed pattern that is obtained from nanoparticles at room temperature.

Transparent conductive coatings are essential for fabrication of a variety of printed electronic devices such as flexible displays and solar cells. We report on a simple method to obtain such coatings by using aqueous dispersions of silver nanoparticles in an evaporative lithography process which is performed directly onto plastic substrates. In essence, a droplet containing silver nanoparticles is placed on top of a metallic mesh, instantaneously spreading over the mesh and the plastic substrate, and after the flow of the dispersion towards the wires of the mesh and drying, a transparent grid composed of the nanoparticles is formed. The silver nanoparticles are tailored to self-sinter upon short exposure to HCl vapors, due to the presence of polyacrylic acid salt on the surface of the particles. Therefore, immediate sintering of the silver nanoparticles in the thin lines of the grid occurs even at room temperature, enabling formation of transparent, flexible conductive grid on heat-sensitive substrates. The process yielded a conductive array having a very low sheet resistance, 9 ± 0.8 Ω/□, and a transparency above 75%. The application of the flexible conductive grid, which can replace conventional and expensive ITO, is demonstrated in an electroluminescent (EL) device.

A novel volatile microemulsion formed by the catanionic surfactant hexadecyltrimethylammonium octylsulfonate (TA(16)So(8)), heptane and water has been explored as a template for producing nanoparticles of hydrophobic organic materials. Butylated hydroxytoluene (BHT) was employed as the model hydrophobic substance. First, the oil-in-water microemulsion was formed, containing TA16So8 as the single emulsifier and BHT dispersed in the volatile microphase. Microstructure characterization by self-diffusion NMR revealed that BHT was indeed incorporated into the oil droplets and that the mean diameter of the main droplet population was 30 nm, larger than in the BHT-free microemulsion. Next, a rapid solvent and water removal by freeze drying allowed converting the microemulsion droplets into nanoparticles in the form of a dry, fine powder. This powder was freely dispersible in water to yield a stable suspension of amorphous BHT particles with a mean size of 19 nm and zeta-potential of +37 mV. The solid nanoparticles in the aqueous dispersion were thus smaller than the initial microemulsion droplets. For comparison, a conventional o/w microemulsion composed of CTAB and sec-butanol was also tested as a template for BHT particle formation by the same process, and it was found that it yielded crystalline particles of micrometre size. On the basis of our results, we anticipate the catanionic microemulsion method to be an efficient one for producing size-controlled, water-dispersible nanoparticles of other hydrophobic organic materials.

The inhibitory effect of ammonium glycyrrhizinate (AG) on crystallization of celecoxib (CXB) nanoparticles in aqueous medium was studied. CXB nanoparticles in powder form were prepared by rapid evaporation of all solvents from a volatile oil-in-water microemulsion. A powder containing 13 wt % CXB was obtained by immediate conversion of microemulsion droplets into nanoparticles by spray drying. CXB was amorphous in this powder, which could be easily dispersed 1 wt % in water as nanoparticles. However, these particles crystallized rapidly upon dispersion, and a significant particle growth was observed. The natural surfactant, AG, which is US Food and Drug Administration approved for oral administration, inhibited crystallization of CXB, enabling a stable dispersion of nanoparticles with average size of 14 nm. Molecular dynamics simulations revealed rapid attachment of glycyrrhizinate to the growing CXB crystal and suggested that crystallization inhibition is due to interactions between the hydrophobic part of glycyrrhizinate and the phenyl moieties of CXB. (C) 2011 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:4390-4400, 2011

We describe here a new and simple method for preparation of polyurea nanocapsules from nanodroplets that were obtained by the phase inversion temperature (PIT) method. In the first stage, a nano-emulsion was prepared, by a heating-cooling cycle, in which the oil phase contained an oil soluble monomer (toluene 2,4-diisocyanate (TDI)). In the second stage, a water-soluble monomer and crosslinker (diethylenetriamine (DETA)) was added, leading to formation of a polymeric shell by an interfacial polycondensation reaction. The new method was demonstrated for obtaining nanocapsules of about 100 nm, in which hexadecane, dodecane, or decane were the core materials, without using any special equipment. The morphology and structure of the nanocapsules were evaluated by attenuated total reflection Fourier transform infrared (ATR-FTIR) measurements and electron microscopy. The thermal behavior of the nanocapsules containing hexadecane was studied by Differential Scanning Calorimetry (DSC) measurements, indicating that such nanocapsules can be utilized in thermal energy storage. Copyright (C) 2010 John Wiley & Sons, Ltd.