A modeling approach to understanding OLED performance improvements arising from spatial variations in guest:host blend ratio

Phosphorescent organic light emitting diodes (OLEDs) suffer from efficiency roll off, where device efficiency rapidly decays at higher luminance. One strategy to minimize this loss of efficiency at higher luminance is the use of non-uniform or graded guest:host blend ratios within the emissive layer. This work applies a multi-scale modeling framework to elucidate the mechanisms by which a non-uniform blend ratio can change the performance of an OLED. Mobility and exciton data are extracted from a kinetic Monte–Carlo model, which is then coupled to a drift diffusion model for fast sampling of the parameter space. The model is applied to OLEDs with uniform, linear, and stepwise graduations in the blend ratio in the emissive layer. The distribution of the guests in the film was found to affect the mobility of the charge carriers, and it was determined that having a graduated guest profile broadened the recombination zone, leading to a reduction in second order annihilation rates. That is, there was a reduction in triplet–triplet and triplet-polaron annihilation. Reducing triplet–triplet and triplet-polaron annihilation would lead to an improvement in device efficiency

Online Stakeholder Interactions in the Early Stage of a Megaproject

The purpose of this paper is to examine the network structure of online stakeholder discussions in the planning stage of a UK public mega project, High Speed Rail. By providing new rail connections between London, Birmingham and Manchester, this project is highly complex as it is embedded in a network of stakeholder relationships that may support or oppose the project. Data drawn from Twitter was analyzed using Social Network Analysis and inductive analysis of user profiles and content. Findings indicate that the majority of online stakeholders oppose the project and form stable clusters. Larger clusters within this network may attempt to deploy power directly in the form of a manipulation strategy while smaller clusters may seek to ally themselves with more powerful groups, a pathway strategy. Overall, the methodology is a useful complement to existing methods and may provide real time insights into the complex, evolving discussions around mega projects

Determination of the influence of the polymer structure and particle size on the film formation process of polymers by atomic force microscopy

The particle size and morphology of a synthetic polymer latex were shown to influence the film formation behavior. Theoretical models predict that small particles coalesce more easily than large colloids do. The influence of particle size and morphology of differently structured lattices on the film-formation process was investigated by atomic force microscopy (AFM). Sequences of AFM images were acquired over a certain temperature range or at room temperature as a function of time. From the resulting images the average particle diameter of the latex particles in the surface layer was determined as a function of the time or temperature. The resulting curves could be compared to observe differences in the film formation kinetics of the different lattices. These AFM studies confirmed that the film formation behavior is influenced by the particle size and particle morphology, but that the core/shell ratio of core-shell particles has no significant influence on the film formation kinetics. © 2002 Elsevier Science Ltd. All rights reserved.Articl

Phosphated polyurethane dispersions: Synthesis, emulsification mechanisms and the effect of the neutralising base

Phosphate-containing polyester macroglycols with different phosphate contents were synthesised from a phosphorus-containing monomer, a dicarboxylic acid and a diol. The macroglycols were then used as a soft segment for the preparation of segmented polyurethane dispersions. Aqueous dispersions were made by phase inversion from the organic solvent after the carboxylic acid groups were neutralized. Phase inversion was found to take place in three distinct stages. The stability and particle size of the polyurethane dispersions were dependent of the amount of carboxylic acid groups present, the degree of neutralisation and the neutralising cations. Metal-neutralized polyurethane dispersions gave smaller particle sizes and the corresponding films showed higher swelling in water due to the ease of hydration. The particle size and stability of the tertiary amine-neutralised polyurethanes were found to be related to the water solubility of the amines at a given dispersion temperature. Particle size increases for the higher alkyl chain neutalising amines due to the poor hydration of the corresponding cations.Conference Pape

The Removal of Copper and Iron from Wine Using a Chelating Resin

An insoluble polymer-supported absorbant, developed for the selective removal of excess copper and iron from wine was tested. Tests conducted on dry white wine with excessive copper and iron showed effective removal of 98% copper (II) and 82 % iron (III). This treatment did not significantly affect the other wine constituents and therefore offers an appropriate alternative to the ferrocyanide treatment

Thermal analysis of controlled-release elastomeric formulations. Part 1. Determination of the solubility limits of sodium lauryl sulphate in elastomers by differential scanning calorimetry

Controlled-release formulations for attaining long-term inhibition of bacterial oxidation of pyrite and the concomitant acid mine drainage were prepared from natural and synthetic rubbers used as binding matrices and sodium lauryl sulphate (SLS) as the active ingredient. The kinetics of release of an active agent from a polymeric matrix depend on several solute-dependent and solute-independent variables. This study focuses on one of the solute-dependent variables, namely, the solubility limit. Since no data on the solubility limits of SLS in natural and synthetic rubbers could be traced, techniques for determining these solubility values were investigated. In this study natural rubber (SMR 20) and synthetic cis-1,4-polyisoprene (IR-80) formulations containing from 0 to 35% SLS were analysed by differential scanning calorimetry (DSC). The thermograms obtained show the appearance of a characteristic melting endotherm when the solubility limit of SLS is exceeded, and this allows the amounts of dissolved and dispersed SLS in the controlled-release formulations to be estimated. The results of the study demonstrate the usefulness of DSC as a convenient and reliable method for determining the solubility limits of solids in elastomers. © 1992.Articl

Thermal analysis of controlled-release elastomeric formulations. Part 1. Determination of the solubility limits of sodium lauryl sulphate in elastomers by differential scanning calorimetry

Controlled-release formulations for attaining long-term inhibition of bacterial oxidation of pyrite and the concomitant acid mine drainage were prepared from natural and synthetic rubbers used as binding matrices and sodium lauryl sulphate (SLS) as the active ingredient. The kinetics of release of an active agent from a polymeric matrix depend on several solute-dependent and solute-independent variables. This study focuses on one of the solute-dependent variables, namely, the solubility limit. Since no data on the solubility limits of SLS in natural and synthetic rubbers could be traced, techniques for determining these solubility values were investigated. In this study natural rubber (SMR 20) and synthetic cis-1,4-polyisoprene (IR-80) formulations containing from 0 to 35% SLS were analysed by differential scanning calorimetry (DSC). The thermograms obtained show the appearance of a characteristic melting endotherm when the solubility limit of SLS is exceeded, and this allows the amounts of dissolved and dispersed SLS in the controlled-release formulations to be estimated. The results of the study demonstrate the usefulness of DSC as a convenient and reliable method for determining the solubility limits of solids in elastomers. © 1992.Articl

NG-migration into double-base inhibitors. II. Diffusion

The maximum sorption of nitroglycerine (NG) in polymeric material was measured in Part I. The results of the sorption is used to determine the average diffusion coefficient for each polymer, utilizing Fick's second law. These values are compared to the chlorine content in the polymer backbone to ascertain whether the chlorine has any influence in lowering the diffusion coefficient.Articl