Investigation of voltage reduction in nanostructure-embedded organic light-emitting diodes

We investigated the reduction of the operating voltage in organic light-emitting diodes containing WO₃ nanoislands. The thickness of the organic layer and the periodicity of the nanoislands were varied in order to quantitatively analyze the electrical changes. The thickness of the N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) layer was varied from 150 nm to 600 nm, and various periodic nanoislands of 300 nm, 330 nm, and 370 nm were fabricated. Two geometric factors, which are the effective length and effective area, influence the operating voltage. The effective length is determined by the relative thickness of the nanoislands compared with the organic thickness, and the reduction of the operating voltage is linearly proportional to the relative thickness. The effective area is a nonlinear function of periodicity, and the voltage is reduced as the periodicity decreases.     

Improving lifetime of phosphorescent organic light-emitting diodes by using a non-conjugated hybrid host

Three hybrid host materials, mCP-PhSiPh3, mCP-L-PhSiPh3, and tBu-mCP-L-PhSiPh3, have been synthesized and characterized for their thermal, morphological, electrochemical, fluorescence, phosphorescence, and electroluminescence properties. The flexible spacer in mCP-L-PhSiPh3 and tBu-mCP-L-PhSiPh3 makes them maintain high triplet energies at about 3.00 eV due to the interruption of π-conjugation. The introduction of the tert-butyl group at the electrochemically active C3 and C6 sites of the carbazole moiety greatly improves thermal and electrochemical stability of the host tBu-mCP-L-PhSiPh3. Blue and green phosphorescent organic light-emitting diodes (PhOLEDs) based on the non-conjugated hosts exhibit external quantum efficiencies at around 15 and 21%, respectively. Higher current densities in PhOLEDs hosted by mCP-PhSiPh3 produce current leakage, resulting in lower efficiencies, especially in green PhOLEDs. The green PhOLEDs using non-conjugated hosts show improved device lifetime in comparison with the mCP-PhSiPh3 based PhOLED because of enhanced morphological stability. The operational stability of the tBu-mCP-L-PhSiPh3 based device is further raised because of improved electrochemical stability by employing the tert-butyl group. Our results demonstrate that both the flexible linkage and the blocking of the electrochemically active sites are crucial measures to realize long-lived PhOLED devices.     

Selective hydrogenation of cinnamaldehyde over reduced graphene oxide supported Pt catalyst

Highly dispersed platinum nanoparticles (NPs) were fabricated on the surface of few-layered reduced graphene oxide (Pt/RGO) via direct ethylene glycol reduction of PtCl₆^2 − in aqueous solution. This well-defined Pt/RGO catalyst was highly selective and active for the hydrogenation of cinnamaldehyde (CAL) to corresponding cinnamyl alcohol (COL) under mild conditions. It was found that the selectivity of COL remained 85.3% at 97.8% CAL conversion in ethanol. These results could be ascribed to the well dispersed Pt NPs on RGO sheets, well dispersion of Pt/RGO in ethanol and ethanol can inhibit the generation of acetals.     

Electrocatalytic oxidation of cyclohexanol on a nickel oxyhydroxide modified nickel electrode in alkaline solutions

Electrocatalytic oxidation of cyclohexanol was investigated with cyclic voltammograms, linear galvanic voltammograms and chronoamperometric responses on a nickel oxyhydroxide modified nickel (NOMN) electrode prepared by cycling the potential of a nickel electrode in the potential range of 0.1 V to 0.6 V (vs SCE) in alkaline solutions. It was found that cyclohexanol was oxidized by NiOOH generated with further electrochemical oxidation of nickel hydroxide during the anodic potential sweep. One of the products of the reaction between cyclohexanol and NiOOH was Ni(OH)₂ which was subsequently oxidized to NiOOH on the anode. This resulted in the appearance of a new anodic peak in cyclic voltammograms compared with the absence of cyclohexanol and this anodic peak strongly depends upon potential scan rates and cyclohexanol concentrations. In addition, the presence of cyclohexanol in NaOH solutions also lead to the decrease of anodic potentials in linear galvanic voltammetric responses and the increase of current densities in chronoamperometric curves. Results showed that the oxidation of cyclohexanol on the NOMN electrode follows the catalytic reaction mechanism.     

Monodispersed microcapsules enclosing ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate

The widespread research of ionic liquids is mainly because of their unique characteristics, which allow the possibility for more efficient reactions and separations in chemical processes. To achieve a successful commercial status, several problems of ionic liquids should be solved, including loss of ionic liquids and high viscosity that effects on fluid flow and mass transfer. In this study, hollow polysulfone microcapsules filled with ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM]PF6 were prepared via a two-stage microfluidic approach. The results of the preparation showed that [BMIM]PF6 was successfully encapsulated with polysulfone, as an encapsulation capacity of 30.8% was achieved. Smaller microcapsules were produced with smaller size of nozzle, lower droplet phase flow rate or higher continuous phase flow rate. The microcapsules had excellent monodispersity and spherical morphology with extremely narrow size distribution. Besides, they had good stability of ionic liquid immobilization. The microfluidic approach has been proved successful to fabricate microcapsules, with advantages of extremely narrow size distribution, easy-controlled operating conditions to obtain different size of microcapsules, possibility for on line observation of preparation process.     

Stability of casein micelle subjected to reversible CO2 acidification: Impact of holding time and chilled storage

Casein micelle stability and reactivity were assessed on milk subjected to reversible acidification by carbonation. Pressurised CO₂ was injected at 4 °C, leading to controlled acidification from 6.63±0.02 to a target pH (5.5 or 5.2). After holding the pressurised milk under these conditions for 15 or 60 min, the pressure was released and the milk pH returned to its initial value under stirring and vacuum degassing. Upon CO₂ treatment, calcium and protein partition, zeta potential and size of casein micelles were restored directly after neutralisation. The rheological properties of the gel obtained by acid coagulation of CO₂-treated milk did not change as a result of carbonation. Micelle hydration increased after neutralisation and during storage. Milk buffering capacity in the pH range of 4.5–5.5 decreased after neutralisation of milk acidified by carbonation, but increased during chilled storage of this milk. Holding time of carbonated milk at low pH was found to have no impact on the physicochemical characteristics of casein micelles and the rheological properties of the gel obtained by acid coagulation of this milk.     

Polyoxometalate as co-catalyst of tetrabutylammonium bromide in polyethylene glycol (PEG) for coupling reaction of CO2 and propylene oxide or ethylene oxide

The coupling reaction of CO₂ and propylene oxide or ethylene oxide to produce corresponding cyclic carbonate in the presence of a catalytic system composed of n-Bu₄NBr, α₂-(n-Bu₄N)₉P₂W₁₇O₆₁(Co²⁺ · Br) (abbreviated as P₂W₁₇Co) and PEG (MW 400) has been investigated. The experimental results indicated that the synthesis of propylene carbonate (PC) or ethylene carbonate (EC) achieved with over 98% yield and 100% selectivity within 1 h at 120 °C by using the above catalyst system. When the catalyst system was recycled, the catalytic activity slowly diminished. Moreover, a plausible mechanism was proposed.     

Effects of primer and annealing treatments on the shear strength between anodized Ti6Al4V and epoxy

The effects of primer and annealing treatments on the shear strength between anodized Ti6Al4V and epoxy were investigated. Primer coating improved the shear strength between anodized Ti alloy and epoxy by up to 81.3% using concurrent curing compared with that of control specimens. After annealing of anodized Ti alloy and applying primer, the shear strength of the specimen was further increased by 6.4% due to the formation of stable TiO₂ transferred from TiO in the anodization process. SEM analysis revealed the specimen without primer and annealing treatments showed adhesive failure between epoxy–alloy interface and discontinuous cohesive failure of epoxy. Primer coating initiated a new interfacial failure mode between the oxide layer and alloy due to the improved bonding strength between epoxy and oxide layer. In addition, annealing and primer treatments generated large tracts of epoxy continuous cohesive failure, showing good agreement with its higher shear strength and work of fracture.