Perspectives on the viscoelasticity and flow behavior of entangled linear and branched polymers

We briefly review the recent advances in the rheology of entangled polymers and identify emerging research trends and outstanding challenges, especially with respect to branched polymers. Emphasis is placed on the role of well-characterized model systems, as well as the synergy of synthesis-characterization, rheometry and modeling/simulations. The theoretical framework for understanding the observed linear and nonlinear rheological phenomena is the tube model which is critically assessed in view of its successes and shortcomings, whereas alternative approaches are briefly discussed. Finally, intriguing experimental findings and controversial issues that merit consistent explanation, such as shear banding instabilities, multiple stress overshoots in transient simple shear and enhanced steady-state elongational viscosity in polymer solutions, are discussed, whereas future directions such as branch point dynamics and anisotropic monomeric friction are outlined.Comment: 25 pages, accepted for publication in Journal of Physics Condensed Matter (August 2015

Thick films of YSZ electrolytes by dip-coating process

Yttria stabilized zirconia (YSZ, 8% Y2O3) thick films were coated on porous Ni-YSZ substrates using the dip-coating process and a suspension with a new formulation. The suspension was obtained by addition of a polymeric matrix in a stable suspension of a commercial YSZ (Tosoh) powders dispersed in an azeotropic MEK-EtOH mixture. The green layers were densified after an optimization of the suspension composition. YSZ Tosoh particles encapsulated by a zirconium alkoxide sol and added with colloidal alkoxide precursor are used to load the suspension. The in situ growth of these colloids increases significantly the layers density after an appropriated heat treatment. The obtained films are continuous, homogeneous and 20 μm thick. Different microstructures are obtained depending on the synthesis parameters of the suspension

Influence of spray drying suspension on the morphology of Fe-based oxygen carriers for chemical looping

Chemical looping reforming (CLR) and chemical looping combustion (CLC) are promising technologies with inherent CO2 capture for transforming fuels into syngas and energy respectively. Circulating oxygen carriers (OC) are used to transfer oxygen from mostly air to the fuel inside the process. Over the past years a variety of materials have been proposed for the role of oxygen carriers, ranging from bulk mineral powders to oxygen carrier particles engineered for shape, size and composition. Iron based materials are very promising and cost effective candidates with minor impact on the environment as compared to the toxic Ni-based OCs. Granulation by the industrial spray-drying technique is suitable for producing oxygen carrier particles with high sphericity and dimensions fit for the fluidized-bed reactors of the CL-process. The lifetime of the oxygen carriers in these reactors however strongly depends on their mechanical properties (as measured by the crushing strength and the attrition resistance) which is related with their morphology and porosity. As this morphology depends on the spray drying suspension, the relation between the additives used in the iron-based suspension and the morphology of the spray-dried particles is investigated in this work [1]. The influence of the concentration of the binder, dispersing agent and solids in the spray-drying suspensions and the intensity of the milling procedure on the morphology and microstructure of the resulting particles is studied by Hg-porosimetry, tapped density, optical microscopy and SEM. A controlled sintering treatment is used during post-processing of these spray-dried particles in order to further improve their mechanical properties before investigating their performance as oxygen carriers in the chemical looping process

Cognitive laboratory experiences and beyond: some ideas for future research

Der Autor diskutiert die Ziele und Inhalte von kognitiven Pretests in der Umfrageforschung und weist darauf hin, dass die Stärke von Pretests zuweilen überschätzt wird, ihre Potentiale hingegen oftmals unausgeschöpft bleiben. Angesichts der Tatsache, dass es keine allgemeinen Richtlinien für einen "guten" Pretest, keine Systematisierung der Forschungspraxis und keinen Konsens über methodische Erwartungen gibt, zeigt der Autor einige notwendige Forschungsperspektiven für die Zukunft auf. Diese sollten neben einer stärkeren Berücksichtigung der zeitlichen und soziologischen Dimension folgende Ziele umfassen: (1) Bewertung der Effektivität von Pretest-Methoden, (2) Entwicklung von empirisch begründeten Richtlinien für das Befragungsdesign und (3) Anpassung der Pretest-Methoden an neue Erhebungsformen, wie z.B. Web- und Unternehmensbefragungen. (ICI

Mass-resolved ion energy measurements at both electrodes of a 13.56 MHz plasma in CF4

The ion energy distributions (IEDs) at the electrodes in a capacitively coupled 13.56 MHz plasma in CF4 have been measured mass resolved with a Balzers quadrupole in combination with a home-built energy analyzer. Mass-resolved determination offers the possibility to compare the IED of different ions achieved in the same sheath. The IEDs have been determined at both the largest and the smallest electrode. Apart from the IEDs of the CF4 species, the IEDs of ionic species in plasmas in argon and nitrogen also were determined. Apart from the CF4 ionic species CF+3, CF+2, CF+, and F+, CHF+2 ions also are present in the CF4 plasma due to residual water in the reactor. Because the CHF+2 ions are not produced in the sheath and because we do not detect elastically scattered ions, the IEDs of these ions show the typical bimodal distribution for rf plasmas which corresponds to an IED of ions which have not collided in the sheath. From these IEDs we can obtain the sheath characteristics, such as the averaged sheath potential. From the IEDs of CF+n ions one can conclude that, in the sheath of the CF4 plasma, a large number of chemical reactions takes place between the CF+n ions and the neutrals

Oxygen-Carrier Development of Calcium Manganite–Based Materials with Perovskite Structure for Chemical-Looping Combustion of Methane

The present work is related to the upscaling of calcium manganite–based oxygen-carrier materials, which have a perovskite structure, both with respect to the use of inexpensive raw materials, i.e., instead of pure chemicals, and the upscaling of production to multitonne batches. Results are presented from the two different stages of material development, i.e., raw material selection and upscaling. The evaluation involves both operation in chemical-looping combustor units of 300 W and 10 kW, and material characterization. In the latter unit, the gas velocities in the riser and in the grid-jet zone of the gas distributor come close to gas velocities of industrial-scale units and, therefore, this unit is also used to assess particle lifetime. Results from the various chemical-looping combustion units and oxygen-carrier materials produced from various raw materials of both high and low purity show that very high degrees of fuel conversion can be reached while achieving very high oxygen-carrier lifetimes. The composition of the oxygen-carrier materials seems robust and flexible with respect to the precursors used in its manufacturing

Sustainable Attrition-resistant oxygen carriers for chemical looping reforming by spray drying

Chemical looping reforming (CLR) and chemical looping combustion (CLC) are promising technologies with inherent CO2 capture for transforming fuels into syngas and energy respectively. Circulating oxygen carriers (OC) are used to transfer oxygen from mostly air to the fuel inside the process. Over the past years a variety of materials have been proposed for the role of oxygen carriers, ranging from bulk mineral powders to oxygen carrier particles engineered for shape, size and composition. A lot of attention has been focused towards the development of Ni-based oxygen carriers due to their good reactivity, conversion and mechanical stability. However the cost, susceptibility towards S-containing impurities and their toxicity are key drivers to develop Ni-free materials. Oxygen carriers based on Fe-oxides are promising because of their lower cost and diminished impact on health and environment. Nevertheless, they also need good thermo-chemo-mechanical properties and thus a sufficient lifetime to be applicable in industrial CL-processes. The longevity of the oxygen carriers in the coupled fluidised bed reactors can be limited by two factors, such as their fragmentation and attrition leading to smaller particles inhibiting their fluidisation as well as their chemical deactivation. Granulation by the industrial spray drying technique appears to yield oxygen carrier particles with high sphericity and good fluidization properties. In addition, a microstructure is obtained that on the one hand aims at thermo-chemo-mechanical integrity and high attrition resistance, and on the other hand at intimate contact between the solid and gaseous phases. However, spray-drying does not appear to be used for producing Fe-based OC thus far. This work emphasises the colloid chemistry of concentrated suspensions used for spray-drying, the development of Fe-based OC by granulation of primary raw materials and the subsequent processing and heat treatment of the oxygen carriers for hydrogen production by chemical looping. To reach the objectives, a systematic approach is used. At first the role of the preparation of the spray dry suspension and the granulation conditions on the morphology of the particles has been investigated. Secondly, the effect of the sinter process was studied. A correlation between tapped density, strength and attrition resistance of the heat-treated materials was observed. Finally, the chemical performance of these Fe-based oxygen carriers was examined in a small scale batch reactor. The chemical composition of the OC was (ex situ) monitored in view of the enhancement of the chemical properties and long term stability thereof by altering the composition and microstructure of synthesised oxygen carriers