Systematic in situ hydration neutron reflectometry study on Nafion thin films.

Reported herein is a neutron reflectometry (NR) study on hydrated Nafion thin films (∼30 nm) on a silicon substrate with native oxide. The Nafion morphology is investigated systematically across the whole relative humidity range using both H2O and D2O vapours to enable a comparative study. By utilising this systematic approach two key results have been obtained. The first is that by leveraging the strong positive scattering signal from the D2O vapour, a complete and systematic water adsorption isotherm (Type II) for a Nafion thin film is produced. Utilising the slight negative scattering signal of the H2O enabled the quantification of the hydration dependent evolution of the formation of Nafion/water lamellae near the substrate surface. The number of lamellae layers increases continuously with hydration, and does not form abruptly. We also report the effects of swelling on the thin films across the relative humidity ranges. The work reported should prove useful in quantifying other hydration dependent properties of Nafion thin films such as conductivity and understanding Nafion/semiconductor based devices, as well as showcasing a NR methodology for other hydrophilic polymers.

Multi-Redox Responsive Behavior in a Mixed-Valence Semiconducting Framework Based on Bis-[1,2,5]-thiadiazolo-tetracyanoquinodimethane.

The two-dimensional (2-D) framework, [Cu(BTDAT)(MeOH)] {BTDAT = bis-[1,2,5]-thiadiazolo-tetracyanoquinodimethane}, possesses remarkable multi-step redox properties, with electrochemical studies revealing six quasi-stable redox states in the solid state. In situ electron paramagnetic resonance and visible-near infrared spectroelectrochemistry elucidated the mechanism for these multi-step redox processes, as well as the optical and electrochromic behavior of the BTDAT ligand and framework. In studying the structural, spectroscopic, and electronic properties of [Cu(BTDAT)(MeOH)], the as-synthesized framework was found to exist in a mixed-valence state with thermally-activated semiconducting behavior. In addition to pressed pellet conductivity measurements, single-crystal conductivity measurements using a pre-patterned polydimethylsiloxane layer on a silicon substrate provide important insights into the anisotropic conduction pathways. As an avenue to further understand the electronic state of [Cu(BTDAT)(MeOH)], computational band structure calculations predicted delocalized electronic transport in the framework. On the balance of probabilities, we propose that [Cu(BTDAT)(MeOH)] is a Mott insulator (i.e., electron correlations cause a metal-insulator transition). This implies that the conductivity is incoherent. However, we are unable to distinguish between activated transport due to Coulombically bound electron-hole pairs and a hopping mechanism. The combined electrochemical, electronic, and optical properties of [Cu(BTDAT)(MeOH)] shine a new light on the experimental and theoretical challenges for electroactive framework materials, which are implicated as the basis of advanced optoelectronic and electrochromic devices.

A novel application of membrane distillation to facilitate nickel recovery from electroplating wastewater.

In many years, the nickel electroplating technique has been applied to coat nickel on other materials for their increased properties. Nickel electroplating has played a vital role in our modern society but also caused considerable environmental concerns due to the mass discharge of its wastewater (i.e. containing nickel and other heavy metals) to the environment. Thus, there is a growing need for treating nickel electroplating wastewater to protect the environment and, in tandem, recover nickel for beneficial use. This study explores a novel application of membrane distillation (MD) for the treatment of nickel electroplating wastewater for a dual purpose: facilitating the nickel recovery and obtaining fresh water. The experimental results demonstrate the technical capability of MD to pre-concentrate nickel in the wastewater (i.e. hence pave the way for subsequent nickel recovery via chemical precipitation or electrodeposition) and extract fresh water. At a low operating feed temperature of 60 °C, the MD process increased the nickel content in the wastewater by more than 100-fold from 0.31 to 33 g/L with only a 20% reduction in the process water flux and obtained pure fresh water. At such high concentration factors, the membrane surface was slightly fouled by inorganic precipitates; however, membrane pore wetting was not evident, confirmed by the purity of the obtained fresh water. The fouled membrane was effectively cleaned using a 3% HCl solution to restore its surface morphology. Finally, the preliminary thermal energy analysis of the combined MD-chemical precipitation/electrodeposition process reveals a considerable reduction in energy consumption of the nickel recovery process.

Grain Boundary Induced Bias Instability in Soluble Acene-Based Thin-Film Transistors.

Since the grain boundaries (GBs) within the semiconductor layer of organic field-effect transistors (OFETs) have a strong influence on device performance, a substantial number of studies have been devoted to controlling the crystallization characteristics of organic semiconductors. We studied the intrinsic effects of GBs within 5,11-bis(triethylsilylethynyl) anthradithiophene (TES-ADT) thin films on the electrical properties of OFETs. The GB density was easily changed by controlling nulceation event in TES-ADT thin films. When the mixing time was increased, the number of aggregates in as-spun TES-ADT thin films were increased and subsequent exposure of the films to 1,2-dichloroethane vapor led to a significant increase in the number of nuleation sites, thereby increasing the GB density of TES-ADT spherulites. The density of GBs strongly influences the angular spread and crystallographic orientation of TES-ADT spherulites. Accordingly, the FETs with higher GB densities showed much poorer electrical characteristics than devices with lower GB density. Especially, GBs provide charge trapping sites which are responsible for bias-stress driven electrical instability. Dielectric surface treatment with a polystyrene brush layer clarified the GB-induced charge trapping by reducing charge trapping at the semiconductor-dielectric interface. Our study provides an understanding on GB induced bias instability for the development of high performance OFETs.