Search results for "Contact"

Perimeter leakage current in polymer light emitting diodes

2009

Observation of leakage current paths through the device perimeter in standard poly(phenylene vinylene)-based light-emitting devices is reported. Perimeter leakage currents govern the diode performance in reverse and low positive bias and exhibit an ohmic character. Current density correlates with the perimeter-to-area ratio thus indicating that leakage currents are mainly confined on polymer regions in the vicinity of metallic contact limits (device perimeter). © 2008 Elsevier B.V. All rights reserved.

Controlling the wetting properties of the Asakura-Oosawa model and applications to spherical confinement.

2012

We demonstrate for the Asakura-Oosawa model and an extension of this model that uses continuous rather than hard potentials, how wetting properties at walls can be easily controlled. By increasing the interaction range of the repulsive wall potential acting on the colloids (while keeping the polymer-wall interactions constant) polymers begin to substitute colloids at walls and the system can be driven from complete wetting of colloids via partial wetting to complete wetting of polymers. As an application, we discuss the morphology and wetting behavior of colloid-polymer mixtures in spherical confinement. We apply the recently developed 'ensemble switch method' where the Hamiltonian is exten…

On the Use of the Nanoindentation Unloading Curve to Measure the Young's Modulus of Polymers on a Nanometer Scale

2005

Summary: The nanoindentation test is a fundamental tool to assess the link between morphology and mechanical properties. The preliminary results of a more exhaustive study about the applicability to polymers of the most used procedure to determine elastic modulus by indentation are reported in this short communication. A departure of the experimental conditions from the theoretical assumptions and results that give rise to the Oliver and Pharr analysis is shown to occur under a wide range of experimental conditions, with applied loads and penetration depths covering several orders of magnitude and using different indenter geometries. Unloading curves with exponents significantly larger than…

Incorporation of Membrane Proteins in Solid-Supported Lipid Layers

1995

Phase Separation of Colloid Polymer Mixtures Under Confinement

2013

Colloid polymer mixtures exhibit vapor-liquid like and liquid-solid like phase transitions in bulk suspensions, and are well-suited model systems to explore confinement effects on these phase transitions. Static aspects of these phenomena are studied by large-scale Monte Carlo simulations, including novel “ensemble switch” methods to estimate excess free energies due to confining walls. The kinetics of phase separation is investigated by a Molecular Dynamics method, where hydrodynamic effects due to the solvent are included via the multiparticle collision dynamics method.

Synthesis of polymeric 1-iminopyridinium ylides as photoreactive polymers

2010

Two synthetic routes to polymeric 1-imino pyridinium ylides as new photoreactive polymeric architectures were investigated. In the first approach, polymerization of newly synthesized 1-imino pyridinium ylide containing monomers yielding their polymeric analogues was achieved by free radical polymerization. Alternatively, reactive precursor polymers were synthesized and converted into the respective 1-imino pyridinium ylide polymers by polymer analogous reactions on reactive precursor polymers. Quantitative conversion of the reactive groups was achieved with pentafluorophenyl ester containing polymers and newly synthesized photoreactive amines as well as by the reaction of poly(4-vinylbenzoy…

Versatile ω-end group functionalization of RAFT polymers using functional methane thiosulfonates

2009

Five different polymers, poly[methyl methacrylate] (PMMA), poly[lauryl methacrylate] (PLMA), poly[diethylene glycol methacrylate] (PDEGMA), poly[N-iso-propylacrylamide] (PNIPA), and poly[styrene] (PS) prepared by the RAFT process and thus terminated with dithioesters were aminolyzed in the presence of S-3-butynyl methane thiosulfonate (MTS), which was synthesized in two steps. Analysis of the polymers by 2D NMR, UV–vis absorbance, and gel permeation chromatogra-phy revealed them to quantitatively carry acetylene end groups connected with disul-fide bridges, indicating that functional MTS reagents can be employed for end group functionalization of RAFT polymers. This versatile method is of ad…

Effect of the elongational flow on morphology and properties of polypropylene/graphene nanoplatelets nanocomposites

2018

Abstract In this work the effect of the presence of graphene nanoplatelets (GnP) on the morphology and mechanical properties of polypropylene/GnP nanocomposites has been investigated when these polymer systems are subjected to non-isothermal elongational flow in a melt spinning operation. The presence of the GnP magnifies the effect of the elongational flow. Indeed, the elastic modulus and the tensile strength of nanocomposites increases with the orientation more than that observed for the pure matrix. Moreover, the elongation at break increases at low values of the draw ratio for the nanocomposites, while, the matrix shows the expected decrease in deformability. These effects have been cor…

On the Reasons for an Anomalous Demixing Behavior of Polymer Solutions

2005

Some extraordinary solutions of polymers in single solvents exhibit two liquid/liquid critical points, one within the usual composition range and a second one in the range of moderate to high polymer concentration. This particularity was studied theoretically by means of a recently established approach, which accounts explicitly for chain connectivity and for the ability of polymer molecules to respond to changes in their environment by conformational rearrangements. On the basis of model calculations, it is shown that the anomalous demixing behavior, i.e., the emergence of a second critical point, is bound to the necessary but not sufficient condition that a thermodynamically very unfavora…

Modification of commercial UF membranes by electrospray deposition of polymers for tailoring physicochemical properties and enhancing filtration perf…

2020

Abstract The main challenge for a widespread use of nanoporous membranes in the removal of ionic contaminants lies in the adjustment of their physicochemical properties to allow adequate ion rejection and mitigate fouling based on the targeted application. Most of the commercial membranes are negatively charged and their use is thus not necessarily relevant for divalent cation rejection. The main objective for researchers is therefore to provide novel tailored membranes by developing specific synthesis or modifying available membranes. It is proposed here to tailor physicochemical properties of a commercial low molecular weight cut-off ultrafiltration membrane by electrospray deposition of …