Optimization of Hybrid Ink Formulation and IPL Sintering Process for Ink-Jet 3D Printing.

Ink-jet 3D printing technology facilitates the use of various materials of ink on each ink-jet head and simultaneous printing of multiple materials. It is suitable for manufacturing to process a complex multifunctional structure such as sensors and printed circuit boards. In this study, a complex structure of a SiO2 insulation layer and a conductive Cu layer was fabricated with photo-curable nano SiO2 ink and Intense Pulsed Light (IPL)-sinterable Cu nano ink using multi-material ink-jet 3D printing technology. A precise photo-cured SiO2 insulation layer was designed by optimizing the operating conditions and the ink rheological properties, and the resistance of the insulation layer was 2.43 × 1013 Ω·cm. On the photo-cured SiO2 insulation layer, a Cu conductive layer was printed by controlling droplet distance. The sintering of the IPL-sinterable nano Cu ink was performed using an IPL sintering process, and electrical and mechanical properties were confirmed according to the annealing temperature and applied voltage. Then, Cu conductive layer was annealed at 100 °C to remove the solvent, and IPL sintered at 700 V. The Cu conductive layer of the complex structure had an electrical property of 29 µΩ·cm and an adhesive property with SiO2 insulation layer of 5B.

Formulation of a graft polymer-containing aqueous yellow ceramic ink for digital ink-jet printing.

We herein reported the preparation of an eco-friendly aqueous yellow ceramic ink and subsequent examination of its printability for ink-jet printing applications. For this purpose, a water based ceramic ink was formulated using ceramic pigments to give a clear color during high-temperature heat treatment (>1000 °C), ultimately yielding an ink suitable for application in ceramic tile decoration. To improve the low dispersion stability of the aqueous ceramic ink compared to that of a conventional organic solvent-based ceramic ink, the pigment particles were dispersed using a graft polymer. More specifically, this graft polymer was composed of polyacrylic acid as the main chain to provide electrostatic repulsion and grafted poly(ethylene glycol) methyl ether methacrylate as the side chain to provide steric hindrance. Furthermore, additive-induced foaming issues were significantly reduced through the use of this graft polymer as a surfactant. The effects of the rheological properties of the prepared ceramic ink and the subsequent operation conditions of the piezoelectric print head were then investigated in detail to optimize the ink jettability and printability.

Single polymer growth dynamics.

In chain-growth polymerization, a chain grows continually to reach thousands of subunits. However, the real-time dynamics of chain growth remains unknown. Using magnetic tweezers, we visualized real-time polymer growth at the single-polymer level. Focusing on ring-opening metathesis polymerization, we found that the extension of a growing polymer under a pulling force does not increase continuously but exhibits wait-and-jump steps. These steps are attributable to the formation and unraveling of conformational entanglements from newly incorporated monomers, whose key features can be recapitulated with molecular dynamics simulations. The configurations of these entanglements appear to play a key role in determining the polymerization rates and the dispersion among individual polymers.

Spatiotemporal catalytic dynamics within single nanocatalysts revealed by single-molecule microscopy.

This review discusses the latest advances in using single-molecule microscopy of fluorogenic reactions to examine and understand the spatiotemporal catalytic behaviors of single metal nanoparticles of various shapes including pseudospheres, nanorods, and nanoplates. Real-time single-turnover kinetics reveal size-, catalysis-, and metal-dependent temporal activity fluctuations of single pseudospherical nanoparticles (<20 nm in diameter). These temporal catalytic dynamics can be related to nanoparticles' dynamic surface restructuring whose timescales and energetics can be quantified. Single-molecule super-resolution catalysis imaging further enables the direct quantification of catalytic activities at different surface sites (i.e., ends vs. sides, or corner, edge vs. facet regions) on single pseudo 1-D and 2-D nanocrystals, and uncovers linear and radial activity gradients within the same surface facets. These spatial activity patterns within single nanocrystals can be attributed to the inhomogeneous distributions of low-coordination surface sites, including corner, edge, and defect sites, among which the distribution of defect sites is correlated with the nanocrystals' morphology and growth mechanisms. A brief discussion is given on the extension of the single-molecule imaging approach to catalysis that does not involve fluorescent molecules.

Quantitative super-resolution imaging uncovers reactivity patterns on single nanocatalysts.

Metal nanoparticles are used as catalysts in a variety of important chemical reactions, and can have a range of different shapes, with facets and sites that differ in catalytic reactivity. To develop better catalysts it is necessary to determine where catalysis occurs on such nanoparticles and what structures are more reactive. Surface science experiments or theory can be used to predict the reactivity of surfaces with a known structure, and the reactivity of nanocatalysts can often be rationalized from a knowledge of their well-defined surface facets. Here, we show that a knowledge of the surface facets of a gold nanorod catalyst is insufficient to predict its reactivity, and we must also consider defects on the surface of the nanorod. We use super-resolution fluorescence microscopy to quantify the catalysis of the nanorods at a temporal resolution of a single catalytic reaction and a spatial resolution of ∼40 nm. We find that within the same surface facets on the sides of a single nanorod, the reactivity is not constant and exhibits a gradient from the centre of the nanorod towards its two ends. Furthermore, the ratio of the reactivity at the ends of the nanorod to the reactivity at the sides varies significantly from nanorod to nanorod, even though they all have the same surface facets.

How does a single Pt nanocatalyst behave in two different reactions? A single-molecule study.

Using single-molecule microscopy of fluorogenic reactions we studied Pt nanoparticle catalysis at single-particle, single-turnover resolution for two reactions: one an oxidative N-deacetylation and the other a reductive N-deoxygenation. These Pt nanoparticles show distinct catalytic kinetics in these two reactions: one following noncompetitive reactant adsorption and the other following competitive reactant adsorption. In both reactions, single nanoparticles exhibit temporal activity fluctuations attributable to dominantly spontaneous surface restructuring. Depending on the reaction sequence, single Pt nanoparticles may or may not show activity correlations in catalyzing both reactions, reflecting the structure insensitivity of the N-deacetylation reaction and the structure sensitivity of the N-deoxygenation reaction.

Single-molecule fluorescence imaging of nanocatalytic processes.

This tutorial review covers recent developments in using single-molecule fluorescence microscopy to study nanoscale catalysis. The single-molecule approach enables following catalytic and electrocatalytic reactions on nanocatalysts, including metal nanoparticles and carbon nanotubes, at single-reaction temporal resolution and nanometer spatial precision. Real-time, in situ, multiplexed measurements are readily achievable under ambient solution conditions. These studies provide unprecedented insights into catalytic mechanism, reactivity, selectivity, and dynamics in spite of the inhomogeneity and temporal variations of catalyst structures. Prospects, generality, and limitations of the single-molecule fluorescence approach for studying nanocatalysis are also discussed.

Hydrogen storage in ni nanoparticle-dispersed multiwalled carbon nanotubes.

Hydrogen storage properties of mutiwalled carbon nanotubes (MWCNTs) with Ni nanoparticles were investigated. The metal nanoparticles were dispersed on MWCNTs surfaces using an incipient wetness impregnation procedure. Ni catalysts have been known to effectively dissociate hydrogen molecules in gas phase, providing atomic hydrogen possible to form chemical bonding with the surfaces of MWCNTs. Hydrogen desorption spectra of MWCNTs with 6 wt % of Ni nanoparticles showed that approximately 2.8 wt % hydrogen was released in the range of 340-520 K. In Kissinger's plot to evaluate the nature of interaction between hydrogen and MWCNTs with Ni nanoparticles, the hydrogen desorption activation energy was measured to be as high as approximately 31 kJ/mol.H(2), which is much higher than the estimates of pristine SWNTs. C-H(n)() stretching vibrations after hydrogenation in FTIR further supported that hydrogen molecules were dissociated when bound to the surfaces of MWCNTs. During cyclic hydrogen absorption/desorption, there was observed no significant decay in hydrogen desorption amount. The hydrogen chemisorption process facilitated by Ni nanopaticles could be suggested as an effective reversible hydrogen storage method.