834 research outputs found
Asphaltene components as organic electronic materials: paving future for a greener environment?
No full textMuch of the world's petroleum resources are in the form of bitumen (heavy and light oil
fractions) mixed with sands and clays. These deposits are generally referred to as oil sands.
Extraction of the bitumen from this source requires a larger input of energy relative to that
required for conventional crude oil. Further, the process requires the use of fresh water and
leaves behind large, but temporary, tailings ponds . The environmental impact of mining
operations in oil sands has been the subject of much media discussion.
Oil sand bitumen contains significant quantities of asphaltenes, which can form deposits in
wells and pipelines, as well as insoluble nanosized aggregates under certain conditions.
Upgrading this bitumen requires the treatment/removal of asphaltenes, which seriously
reduces the cost-effectiveness associated with the process. This is complicated by the fact that
asphaltene structure and composition differ depending upon their source. However, they are
thought to be composed of central structures of extended aromatic systems with alkyl or
alkylthiol substituents and/or bridges[3,4]. There remains a need in the art for new uses of
asphaltenes [5]. New uses for asphaltenes help reducing the environmental burden of bitumen
extraction in which they are often considered a waste product.
Here we report the first results of an exploratory study focusing on the investigation of
organic materials comprising asphaltenes from different sources, to evaluate them as active
layers in (opto)electronic devices
Structure of 6π-electron four-membered rings containing second-row atoms
No full textAn ab initio quantum chemical study is presented on 6π-electron four-membered 1,3-X2Z2Y2Z′2 (X = P, S; Y = C, N, O, P, S; Z, Z′ = H, lone pair) rings. Stationary points on the potential energy surfaces were fully optimized within the symmetry constraints using SCF/6-31G* and MP2/6-31G* methods and characterized by calculating the harmonic vibrational frequencies of the normal modes. It is shown that besides experimentally known 6π-electron four-membered rings (S2N2, S42+) several 1,3-X2Z2Y2Z′2 rings possess a planar (aromatic) configuration. Alternatively, a distorted Cs structure or a puckered C2v structure with a trans-annular bond are found. The theoretical geometric parameters are in good agreement with available X-ray crystallographic data on a number of these compounds, their derivatives, or their complexes with transition metals. The preference for a planar, distorted, or puckered structure is rationalized in terms of 1,3-repulsive interactions and stabilizing deformations of the planar rings
Hogere rendementen in polymere zonnecellen met nieuwe materialen en celconcepten
No full textZonnecellen waarin de fotoactieve laag bestaat uit polymeren zijn in principe aantrekkelijk voor grootschalige fotovoltïsche energieconversie. De essentieële gedachte is dat goede rendementen gecombineerd worden met snelle productietechnologieen, gebaseerd op druktechnieken, die het in de toekomst mogelijk maken zonnecellen goedkoop te produceren met snelheden van enkele vierkante meters per seconde. Nieuwe materialen en slimme zonnecelconcepten die het rendement kunnen verhogen zijn essentieel om deze belofte waar te maken
Design and experimental validation of low stiffness aerostatic thrust bearings
No full textLinear aerostatic bearings are frequently used in high precision stages for their advantageous bearing properties, with low friction and absence of stick-slip being most notable. To improve relatively low out-of-plane stiffness of air bearings, pre-loading is applied. A common method of pre-loading is by utilizing vacuum, where a constant vacuum force decreases film height resulting in increased stiffness. Other methods for increasing stiffness are available, which is an active field of research. However, high stiffness results in strong coupling between bearing and running surface, transferring unwanted external vibrations. The amount of vibration transfer is quantified as transmissibility, which is the ratio of displacements between coupled surfaces. This property is frequency dependent. To reduce disturbance from external vibrations, this research focusses on reducing air bearing stiffness by combining pressurized and vacuum bearing pads, which to the knowledge of the author has not yet been researched. To analyse stiffness behaviour, air bearings have been modelled based on Reynolds equation. The effect of a vibrating running surface is modelled by linear perturbation of Reynolds equation. Resulting equations have been solved with a self developed finite volume method code, resulting in air film stiffness and damping as a function of frequency in an computationally efficient manner. Two combinations of thrust and vacuum bearings with a stable low stiffness operating point have been designed with the developed models. By offsetting vacuum and thrust surfaces or by using a micrometer pocket in the thrust bearing surface, vacuum and thrust stiffness cancel out, creating a range of low stiffness between regions with higher stiffness. To validate the models, air bearings have been manufactured. Measurements on restrictor properties have shown the literature model to be invalid for realistic pressure drops. Without taking the measured restrictor behaviour into account, model and measurement will not match. Also shown is that controlling surfaces flatness is essential for predictable bearing behaviour. Performance of available production methods is thoroughly researched. Model and measurement correspondence can only be achieved by taking surface properties into account. Also, the low tip-tilt stiffness of a single air bearing has been found to negatively effect measurements on film height. By using three bearings in the measurement set-up, tip-tilt stiffness has been significantly increased. This reduces measurement uncertainty. By taking these findings into account, excellent agreement between measurements and model has been achieved. This clears the way for development of a low stiffness prototype, combining thrust and vacuum bearings. Ideas on model improvement and prototype development are shared in the recommendations.Mechanical, Maritime and Materials EngineeringPrecision and Microsystems Engineerin
Red, green, and blue quantum dot LEDs with solution processable ZnO nanocrystal electron injection layers
No full textZnO nanocrystals are presented as an electron injection layer for red, green, and blue light-emitting diodes (LEDs) based on core–shell CdSe/ZnS quantum dots (QDs). The deposition of ZnO nanocrystals from isopropanol permits fabricating multilayer QD-LEDs that include both hole and electron transport layers by simple solution processing. The ZnO nanocrystals improve electron injection in the light-emitting QD layer as evidenced from a decreased turn-on voltage and a reduction of emission originating from other layers than the QD layer of the LED
Efficient synthesis of high-spin meta-para-oligoanilines
No full textA series of oligo(N-methylaniline)s consisting of alternating meta and para substituted benzene rings up to 8 units has been synthesized via palladium-catalyzed coupling reactions. These oligo(N-methylaniline)s can be oxidized reversibly to the corresponding oligo(cation radical)s, which are stable at ambient temperature and possess a high-spin ground state as evidenced by ESR spectroscopy
Spacer length dependence of photoinduced electron transfer in heterosupramolecular assemblies of TiO2 nanoparticles and terthiophene
No full textHeterosupramol. assemblies of TiO2 nanoparticles
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