Rapid Macroscopic-Scale Assembly of Ag Nanowires at the Water/Air Interface.

Rapid macroscopic-scale assembly of Ag nanowires was demonstrated through facile self-assembly at the water/air interface. This self-assembly was induced by heating due to the surface tension effect and convection. Interestingly, a rippled hairstyle superstructure was observed when the aqueous dispersions of thinner Ag nanowires were heated. Applying the Euler buckling theory for a set of aligned Ag nanowires, it was found that the water surface tension was sufficient to bend or buckle these free Ag nanowires trapped between two nanowire stripes, which resulted in the formation of the rippled hairstyle superstructure. However, the formation of the nanowire stripes was driven by steric repulsion of nanowires along with their short-range van der Waals interactions and later lateral capillary attraction between large building blocks. Such control over self-assembly is key for designing hierarchically ordered structures, which opens a new opportunity in the exploration of novel properties and the development of new applications.

Synthesis of silver nanoplates by two-dimensional oriented attachment.

Synthesis of silver nanoplates was studied in the modified polyol method, where the nucleation and seed stage occurred in a poly(ethylene glycol) (PEG)-water mixture solution, and the growth stage happened in the PEG environment. The morphological evolution of nanoplates was characterized using UV, SEM, and TEM. Interestingly, plane nanostructures with unusual jagged edges were finally formed in our modified polyol method. Using TEM, we observed the medium state of fusion between two nanoplates, resulting in generating unusual jagged edges. Therefore, a novel two-dimensional oriented attachment occurred in our modified polyol method, which involves smaller nanoplates as the building blocks. Further control experiments showed that the presence of water could break this kinetic preferred reactivity, leading to the formation of nanoparticles.

High-Performance Stretchable Conductive Composite Fibers from Surface-Modified Silver Nanowires and Thermoplastic Polyurethane by Wet Spinning.

Highly stretchable and conductive fibers have attracted great interest as a fundamental building block for the next generation of textile-based electronics. Because of its high conductivity and high aspect ratio, the Ag nanowire (AgNW) has been considered one of the most promising conducting materials for the percolation network-based conductive films and composites. However, the poor dispersibility of AgNWs in hydrophobic polymers has hindered their application to stretchable conductive composite fibers. In this paper, we present a highly stretchable and conductive composite fiber from the co-spinning of surface-modified AgNWs and thermoplastic polyurethane (PU). The surface modification of AgNWs with a polyethylene glycol derivative improved the compatibility of PU and AgNWs, which allowed the NWs to disperse homogeneously in the elastomeric matrix, forming effective percolation networks and causing the composite fiber to show enhanced electrical and mechanical performance. The maximum AgNW mass fraction in the composite fiber was 75.9 wt %, and its initial electrical conductivity was as high as 14 205 S/cm. The composite fibers also exhibited superior stretchability: the maximum rupture strain of the composite fiber with 14.6 wt % AgNW was 786%, and the composite fiber was also conductive even when it was stretched up to 200%. In addition, 2-dimensional (2-D) Ag nanoplates were added to the AgNW/PU composite fibers to increase the stability of the conductive network under repeated stretching and releasing. The Ag nanoplates acted as a bridge to effectively prevent the AgNWs from slippage and greatly improved the stability of the conductive network.

Ultrasensitive Wearable Pressure Sensors Assembled by Surface-Patterned Polyolefin Elastomer Nanofiber Membrane Interpenetrated with Silver Nanowires.

Wearable pressure sensors with ultrahigh sensitivity and flexibility have garnered tremendous attention because of their abilities to mimic the human somatosensory system and perceive surrounding pressure distribution. Herein, an ultrasensitive pressure sensor was fabricated with surface-patterned nanofibrous membranes (SPNMs) via a facile replica method from available plain-weaved nylon textiles. The SPNMs were composed of internal three-dimensional interpenetrating polyolefin elastomer nanofibers and silver nanowires (Ag NWs). The effects of the geometry of surface patterns and the density of the Ag NW network on the sensing performance of the assembled pressure sensor were systematically investigated. The results indicated that clavate groove-shaped surface patterns improved the sensitivity and a larger groove spacing contributed to higher sensitivities, whereas denser Ag NWs would reduce the sensing performance. The optimal pressure sensor assembled with SPNMs-45 and a Ag NW fraction of 3.8% showed high sensitivity (19.4 kPa-1) below the pressure of 2.76 kPa, a low detection limit (<1.6 Pa), fast response (30 and 42 ms), as well as excellent durability. These outstanding performances demonstrated its promising potential for wearable electronic applications, like detecting the spatial pressure distribution and monitoring human muscle motions.

Hollow porous Cu particles from silica-encapsulated Cu2O nanoparticle aggregates effectively catalyze 4-nitrophenol reduction.

A hollow metal micro/nanomaterial with a porous wall is one of the most attractive structures for catalysts. The synthesis of hollow porous Cu particles remains a challenge due to their air-sensitive characteristics. In this study, we report a facile and scalable method for the preparation of high-quality hollow porous Cu particles in the range of 500 nm-1.5 µm with a well-defined structure from Cu2O nanoparticle aggregates (NPAs). The synthetic procedure involves the silica-encapsulation and depth-controlled reduction of Cu2O NPAs followed by heat-treatment in air and selective removal of the encapsulating layer. The catalytic performance of the hollow porous Cu particles was evaluated through the catalytic reduction of 4-nitrophenol with NaBH4 as a model reaction. The hollow porous Cu particles exhibited a high activity factor, K = 186 s-1 g-1, which is the highest K value obtained among the unsupported Cu catalysts to date. And the K value is better than that of some noble metal catalysts, such as Au, Ag, and Pd. In addition, the catalyst could be easily separated from the reaction system and still possessed high activity as well as stability in recycled reactions.

The facile synthesis of Cu@SiO2 yolk-shell nanoparticles via a disproportionation reaction of silica-encapsulated Cu2O nanoparticle aggregates.

Encapsulation of a nanoparticle (NP) followed by tailoring of the core materials is an effective strategy for constructing hollow and yolk-shell NPs. Herein, we report the facile synthesis of Cu@SiO2 yolk-shell NPs by converting the silica-encapsulated Cu2O nanoparticle aggregates (NPAs) via a disproportionation reaction. This method is extremely simple and scalable. In addition, all reactions were conducted in air and water solutions that are easily scalable to a mass production scale.

Assembling Ag nanoparticles into morphology controlled secondary structures on loosely packed self-assembled monolayers.

An efficient route for the assembling of Ag nanoparticles (NPs) onto solution phase Ag(palmitate) bilayer structure has been developed. Two dimension (2D) arrays of Ag NPs on Ag(palmitate) were prepared by treating palmitate stabilized Ag NPs with the as-synthesized Ag(palmitate) or ribbon-shaped Ag(palmitate) templates. The interaction between long chain carboxylate surfactants of Ag NPs and the protruding aliphatic chains of the loosely packed self-assembled monolayer may play a role in directing the self-assembly of NPs in monolayer fashion. In addition, facile method to control morphology of Ag(carboxylates) from micro-flakes to micro-ribbons was also demonstrated.

Facile synthesis and size control of spherical aggregates composed of Cu(2)O nanoparticles.

The secondary structures of Cu(2)O nanoparticles were prepared in aqueous solution utilizing self-assembled aggregation process. By introducing polyacrylamide (PAM) as a secondary surfactant, the colloidal nanoparticle aggregates (CNAs) become uniform in size and exhibit spherical shape compared to the random aggregates without PAM. The size of CNA can be systematically controlled from 300nm to 1000nm by varying PAM concentration. The formation mechanism was explained based on a conventional colloidal particle formation mechanism. These control methods may generally be applied to the preparation of secondary nanoparticle structures.

The simple and facile methods to improve dispersion stability of nanoparticles: different chain length alkylcarboxylate mixtures.

The dispersion stability of the Ag nanoparticles with a mixed surfactant of alkylcarboxylates was quantitatively examined, compared with those of the Ag nanoparticles with a single molecule surfactant of alkylcarboxylates. The nanoparticles with a mixed surfactants have far-improved dispersion stability compared with those with normal alkylcarboxylates. The surface roughness of the surfactant layer might be responsible for the improved dispersion stability through the enhanced solvent-surfactant interaction and the decrease in inter-particle surfactant interactions.

Gels from mixed ligand silver(I) carboxylates: a promising approach for gel formation utilizing surface modifications.

Mixtures of Ag(hexanoate) and Ag(palmitate) give thermoreversible gels at very low concentration in toluene. The framework of the gel is composed of the branched nanosized fibers, contrary to the microsized wire precipitates of silver(I) carboxylates. The randomness of mixed-ligand silver(I) carboxylate polymeric chains hinders the crystallization process, resulting in very thin fibrils. This may be a new approach to design and control the properties of materials, which do not have properties involving gels or nanostructures in a conventional process.

Synthesis of poly(epsilon-caprolactone)-b-poly(gamma-benzyl-L-glutamic acid) block copolymer using amino organic calcium catalyst.

A biodegradable two block copolymer, poly(epsilon-caprolactone)-b- poly(gamma-benzyl-L-glutamic acid) (PCL-PBLG) was synthesized successfully by ring-opening polymerization of N-carboxyanhydride of gamma-benzyl-L-glutamate (BLG-NCA) with aminophenyl-terminated PCL as a macroinitiator. The aminophenethoxyl-terminated PCL was prepared via hydrogenation of a 4-nitrophenethoxyl-terminated PCL, which was novelly obtained from the polymerization of epsilon-caprolactone (CL) initiated by amino calcium 4-nitrobenzoxide. The structures of the block copolymer and its precursors from the initial step of PCL were confirmed and investigated by 1H NMR, FT-IR, GPC, and FT-ICRMS analyses and DSC measurements.