Silver Nanowire Networks: Ways to Enhance Their Physical Properties and Stability.

Silver nanowire (AgNW) networks have been intensively investigated in recent years. Thanks to their attractive physical properties in terms of optical transparency and electrical conductivity, as well as their mechanical performance, AgNW networks are promising transparent electrodes (TE) for several devices, such as solar cells, transparent heaters, touch screens or light-emitting devices. However, morphological instabilities, low adhesion to the substrate, surface roughness and ageing issues may limit their broader use and need to be tackled for a successful performance and long working lifetime. The aim of the present work is to highlight efficient strategies to optimize the physical properties of AgNW networks. In order to situate our work in relation to existing literature, we briefly reported recent studies which investigated physical properties of AgNW networks. First, we investigated the optimization of optical transparency and electrical conductivity by comparing two types of AgNWs with different morphologies, including PVP layer and AgNW dimensions. In addition, their response to thermal treatment was deeply investigated. Then, zinc oxide (ZnO) and tin oxide (SnO2) protective films deposited by Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD) were compared for one type of AgNW. We clearly demonstrated that coating AgNW networks with these thin oxide layers is an efficient approach to enhance the morphological stability of AgNWs when subjected to thermal stress. Finally, we discussed the main future challenges linked with AgNW networks optimization processes.

Advanced technologies for the fabrication of MOF thin films.

Metal-organic framework (MOF) thin films represent a milestone in the development of future technological breakthroughs. The processability of MOFs as films on surfaces together with their major features (i.e. tunable porosity, large internal surface area, and high crystallinity) is broadening their range of applications to areas such as gas sensing, microelectronics, photovoltaics, and membrane-based separation technologies. Despite the recent attention that MOF thin films have received, many challenges still need to be addressed for their manufacturing and integrability, especially when an industrial scale-up perspective is envisioned. In this brief review, we introduce several appealing approaches that have been developed in the last few years. First, a summary of liquid phase strategies that comprise microfluidic methods and supersaturation-driven crystallization processes is described. Then, gas phase approaches based on atomic layer deposition (ALD) are also presented.

Transparent and Mechanically Resistant Silver-Nanowire-Based Low-Emissivity Coatings.

This article reports on the fabrication and investigation of low-emissivity (low-E) coatings based on random networks of silver nanowires (AgNWs). The transparent layers based on AgNWs do exhibit low emissivity while being still transparent: an overall emissivity as low as 0.21 at 78% total transmittance was obtained. A simple physical model allows to rationalize the emissivity-transparency dependence and a good agreement with experimental data is observed. This model demonstrates the role played by AgNWs which partially reflect IR photons emitted by the substrate, exacerbating then the presence of AgNWs and lowering the total emissivity. The potential use of such layers in functional devices is hampered by the poor intrinsic surface adhesion of the AgNWs, which renders the coating fragile and prone to mechanical damaging. Two very efficient encapsulation processes based on the deposition of a conformal alumina thin film using the spatial atomic layer deposition technique and the solution processed layer deposition of a polysiloxane varnish have been developed to thwart this weakness. Both coatings combine sturdy mechanical resistance relying on a strong interfacial adhesion and excellent optical transmittance properties. The performances for the mechanically resistant low-E coatings achieve an overall emissivity as low as 0.34 at 74% total transparency. The set of optical properties and mechanical resistance of the reported AgNWs based low-E coatings combined with the ease of fabrication and the cost-effective production process make it an excellent candidate for a wide set of applications, including smart windows for energy-saving buildings.

On the effect of the nature of counterions on the self-assembly of polyoxyethylene alkyl ether carboxylic acids.

In this contribution, we investigate the effect of the type of counterion on the properties of dilute solutions of polyoxyethylene alkyl ether carboxylic acids. Two different surfactants, presenting an oleic acid alkyl chain and on-average five and nine ethylene oxide units, and terminated by a weakly anionic carboxymethyl group were studied. The surfactants were gradually ionized with sodium hydroxide, arginine, and choline hydroxide. The solutions properties were probed by light scattering, electrophoretic mobility, density and sound velocity measurements, as well as by small-angle neutron scattering. To our initial surprise, no specific effect arising from the nature of the counterion could be determined. We ascribe this phenomenon to the fact that the presence of the ethylene oxide units markedly dilutes the surfactant head group charge density, reducing counterion condensation and subsequent counterion specific effects.