Alexander Kamyshny

Triggering the Sintering of Silver Nanoparticles at Room Temperature

A new approach to achieve coalescence and sintering of metallic nanoparticles at room temperature is presented. It was discovered that silver nanoparticles behave as soft particles when they come into contact with oppositely charged polyelectrolytes and undergo a spontaneous coalescence process, even without heating. Utilizing this finding in printing conductive patterns, which are composed of silver nanoparticles, enables achieving high conductivities even at room temperature. Due to the sintering of nanoparticles at room temperature, the formation of conductive patterns on plastic substrates and even on paper is made possible. The resulting high conductivity, 20% of that for bulk silver, enabled fabrication of various devices as demonstrated by inkjet printing of a plastic electroluminescent device.

Metal-based Inkjet Inks for Printed Electronics

A review on applications of metal-based inkjet inks for printed electronics with a particular focus on inks con- taining metal nanoparticles, complexes and metallo-organic compounds. The review describes the preparation of such inks and obtaining conductive patterns by using various sintering methods: thermal, photonic, microwave, plasma, electri- cal, and chemically triggered. Various applications of metal-based inkjet inks (metallization of solar cell, RFID antennas, OLEDs, thin film transistors, electroluminescence devices) are reviewed.

Copper Nanoparticles for Printed Electronics: Routes Towards Achieving Oxidation Stability

In the past few years, the synthesis of Cu nanoparticles has attracted much attention because of its huge potential for replacing expensive nano silver inks utilized in conductive printing. A major problem in utilizing these copper nanoparticles is their inherent tendency to oxidize in ambient conditions. Recently, there have been several reports presenting various approaches which demonstrate that copper nanoparticles can resist oxidation under ambient conditions, if they are coated by a proper protective layer. This layer may consist of an organic polymer, alkene chains, amorphous carbon or graphenes, or inorganic materials such as silica, or an inert metal. Such coated copper nanoparticles enable achieving high conductivities by direct printing of conductive patterns. These approaches open new possibilities in printed electronics, for example by using copper based inkjet inks to form various devices such as solar cells, Radio Frequency Identification (RFID) tags, and electroluminescence devices. This paper provides a review on the synthesis of copper nanoparticles, mainly by wet chemistry routes, and their utilization in printed electronics.

Plasma and Microwave Flash Sintering of a Tailored Silver Nanoparticle Ink, Yielding 60% Bulk Conductivity on Cost‐Effective Polymer Foils

A combination of plasma and microwave flash sintering is used to sinter an inkjet-printed and tailored silver nanoparticle formulation. By using two sintering techniques sequentially, the obtained conductivity is 60%, while keeping the processing temperature well below the glass transition temperature (T(g)) of the used polymer substrate. This approach leads to highly conductive features on cost-effective polymer substrates in relatively short times, which are compatible with roll-to-roll (R2R) production. An electroluminescence device is prepared as an example.

Polymer-surfactant interactions: binding mechanism of sodium dodecyl sulfate to poly(diallyldimethylammonium chloride).

The binding mechanism of poly(diallyldimethylammonium chloride), PDAC, and sodium dodecyl sulfate, SDS, has been comprehensively studied by combining binding isotherms data with microcalorimetry, zeta potential, and conductivity measurements, as well as ab initio quantum mechanical calculations. The obtained results demonstrate that surfactant-polymer interaction is governed by both electrostatic and hydrophobic interactions, and is cooperative in the presence of salt. This binding results in the formation of nanoparticles, which are positively or negatively charged depending on the molar ratio of surfactant to PDAC monomeric units. From microcalorimetry data it was concluded that the exothermic character of the interaction diminishes with the increase in the surfactant/polymer ratio as well as with an increase in electrolyte concentration.

“Nano to nano” electrodeposition of WO3 crystalline nanoparticles for electrochromic coatings

A “nano to nano” electrodeposition approach for preparing nano-structured thin films from the dispersion of nano-objects is reported. A typical WO3 system is demonstrated, where nanocrystalline films are electrodeposited onto transparent conductive electrodes such as ITO and Ag grid printed PET (Ag grid/PET) from the water dispersion of WO3 nanoparticles without applying high potential, adding surfactants or polymers. The process is based on the reduction of WO3, which eliminates the electrostatic repulsion between the nanoparticles causing film deposition on the cathode. The reduced WO3 (HWO3) is conductive, thus it allows further film growth towards higher thickness and coverage. The electrodeposited films consist of stacked crystalline nanoparticles, which provide a highly active surface area, facilitate the penetration of electrolyte and the intercalation/deintercalation of Li+ in the nanocrystals and therefore result in outstanding electrochromic performance and stability (92% contrast, 9 s coloring and 15 s bleaching, retaining 76% contrast after 1000 coloring–bleaching cycles). The thickness, electrochromic performance and surface coverage of the films are well tuned by potential and time. This novel “nano to nano” electrodeposition approach based on the electrochemical redox of nano-objects can be extended to various transition metal oxide nano-objects with different sizes and shapes.

VO2/Si-Al gel nanocomposite thermochromic smart foils: Largely enhanced luminous transmittance and solar modulation

VO2 nanoparticles with a dimension of approximately 20 nm were obtained by simple mechanical bead-milling method, which were well dispersed in transparent silica-alumina (Si-Al) gel matrix to form nanocomposites. The VO2/Si-Al gel thermochromic nanocomposite foils were fabricated with various VO2 solid contents and foil thickness. With 10% VO2 loading and 3 μm foil thickness, high luminous transmittance (T(lum(20°C))=63.7% and T(lum(90°C))=54.4%), and large solar modulation ability (ΔTsol=12%) can be obtained which surpasses the best reported results (nanoporous films:T(lum(20°C))=43.3%, T(lum(90°C))=39.9% and ΔTsol=14.1%). This current approach provided a simple and scalable preparation method with the best combined thermochromic performance.

Merging of metal nanoparticles driven by selective wettability of silver nanostructures

The welding and sintering of nanomaterials is relevant, for example, to form electrical contacts between metallic particles in printed electronic devices. Usually the welding of nanoparticles is achieved at high temperatures. Here we find that merging of two different metals, silver and gold nanoparticles, occurs on contact at room temperature. The merging process was investigated by experimental and molecular dynamics simulations. We discovered that the merging of these particles is driven by selective wettability of silver nanoparticles, independent of their size and shape (spheres or rods); silver behaves as a soft matter, whereas gold as a hard surface being wetted and retaining its original morphology. During that process, the silver atoms move towards the surface of the Au nanoparticles and wrap the Au nanoparticles in a pulling up-like process, leading to the wetting of Au nanoparticles.

Interfacial Properties of Hydrophobically Modified Biomolecules: Fundamental Aspects and Applications

This review describes the interfacial behavior of biomolecules, which were converted to more hydrophobic derivatives by covalent attachment of hydrophobic chains. The molecules presented are proteins (glucose oxidase, immunoglobulin G, gelatin, ovalbumin) and polysaccharides (carboxymethylcellulose, pullulan). In general, it was found that such hydrophobically modified biomolecules have enhanced surface activity and ability to penetrate into phospholipid monolayers. In addition, it has been demonstrated, that such molecules can be used as efficient emulsifiers and foaming agents, and in unique biomedical application based on combining the surface activity and recognition ability. †Visiting Professor at Casali Institute of Applied Chemistry.

ADSORPTION OF HYDROPHOBIZED IGG AND GELATIN ONTO PHOSPHATIDYL CHOLINE-COATED SILICA

Abstract Covalent modification of human IgG and gelatin (type A) by fatty acid esters (C8, C12 and C16) of N-hydroxysuccinimide was carried out. Preparations of hydrophobized IgG containing 9 and 25 attached caprylic and 25 palmitic chains and preparations of gelatin with low and high degree of modification were obtained. The adsorption of unmodified and modified proteins at a hydrophobic surface obtained by coating silica with a phosphatidyl choline monolayer was studied. It was found that an increase in the proteins’ hydrophobicity leads to an increase in their adsorption determining by hydrophobic binding which overcomes the electrostatic repulsion between the negatively charged surface and the negatively charged protein molecules. An increase in the IgG hydrophobicity also resulted in the formation of a more compact monolayer. An increase in gelatin adsorption after its hydrophobization led to either the formation of a more compact monolayer or the formation of a more condensed molecular configuration after attachment of alkyl chains. For both proteins the adsorption can be accompanied by penetration of these chains into the phospholipid monolayer.