184 research outputs found
How coherent structures dominate the residence time in a bubble wake: an experimental example
Mixing timescales and residence times in reactive multiphase flows can be
essential for product selectivity. For instance when a gas species is consumed
e.g. by a competitive consecutive reaction with moderate reaction kinetics
where reaction timescales are comparable to relevant mixing timescales. To
point out the importance of the details of the fluid flow, we analyze
experimental velocity data from a Taylor bubble wake by means of Lagrangian
methods. By adjusting the channel diameter in which the Taylor bubble rises,
and thus the rise velocity, we obtain three different wake regimes. Remarkably
the normalized residence times of passive particles advected in the wake
velocity field show a peak for intermediate rise velocities. This fact seems
unintuitive at first glance because one expects a faster removal of passive
tracers for a faster overall flow rate. However, the details of the flow
topology analyzed using Finite Time Lyapunov Exponent (FTLE) fields and
Lagrangian Coherent Structures (LCS) reveal the existence of a very coherent
vortical pattern in the bubble wake which explains the long residence times.
The increased residence times within the vortical structure and the close
bubble interface acting as a constant gas species source could enhance side
product generation of a hypothetical competitive consecutive reaction, where
the first reaction with the gas species forms the desired product and the
second the side product.Comment: 13 pages, 7 figures, 1 tabl
New Guanidine-Pyridine Copper Complexes and Their Application in ATRP
The guanidine hybrid ligands, (tetramethylguanidine)methylenepyridine (TMGpy) and (dimethylethyleneguanidine)methylenepyridine (DMEGpy), were proven to be able to stabilize copper complexes active in the solvent-free polymerization of styrene at 110 degrees C using 1-phenylethylbromide as the initiator. The polymerization proceeded after first-order kinetics, and polystyrenes with polydispersities around 1.2 could be obtained. Using the ligand, DMEGpy, three new copper guanidine-pyridine complexes could be synthesized and structurally characterized. Their structural characteristics are discussed
New Guanidine-Pyridine Copper Complexes and Their Application in ATRP
The guanidine hybrid ligands, (tetramethylguanidine)methylenepyridine (TMGpy) and (dimethylethyleneguanidine)methylenepyridine (DMEGpy), were proven to be able to stabilize copper complexes active in the solvent-free polymerization of styrene at 110 degrees C using 1-phenylethylbromide as the initiator. The polymerization proceeded after first-order kinetics, and polystyrenes with polydispersities around 1.2 could be obtained. Using the ligand, DMEGpy, three new copper guanidine-pyridine complexes could be synthesized and structurally characterized. Their structural characteristics are discussed
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Digitalizing the Chemical Landscape: A Comprehensive Overview and Progress Report of NFDI4Chem
The Chemistry consortium NFDI4Chem aims to digitalise key steps in chemical research, supporting scientists in managing research data throughout its life cycle. The SmartLab, embedded in a federation of services, integrates various tools such as electronic lab notebooks, data repositories, and search services, to create a smart lab environment for structured data gathering. Utilizing terminology services and adhering to data format standards, NFDI4Chem promotes secure and FAIR data sharing, fostering collaboration and expediting scientific discoveries. This development is supported by community building measures, workshops, and training initiatives, along with collaboration on international minimum information standards
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NFDI4Chem - A Research Data Network for International Chemistry
Research data provide evidence for the validation of scientific hypotheses in most areas of science. Open access to them is the basis for true peer review of scientific results and publications. Hence, research data are at the heart of the scientific method as a whole. The value of openly sharing research data has by now been recognized by scientists, funders and politicians. Today, new research results are increasingly obtained by drawing on existing data. Many organisations such as the Research Data Alliance (RDA), the goFAIR initiative, and not least IUPAC are supporting and promoting the collection and curation of research data. One of the remaining challenges is to find matching data sets, to understand them and to reuse them for your own purpose. As a consequence, we urgently need better research data management
Towards New Robust Zn(II) Complexes for the Ring-Opening Polymerization of Lactide Under Industrially Relevant Conditions
The synthesis of bio-based and biodegradable plastics is a hot topic in research due to growing environmental problems caused by omnipresent plastics. As a result, polylactide, which has been known for years, has seen a tremendous increase in industrial production. Nevertheless, the manufacturing process using the toxic catalyst Sn(Oct)2 is very critical. As an alternative, five zinc acetate complexes have been synthesized with Schiff base-like ligands that exhibit high activity in the ring-opening polymerization of non-purified lactide. The systems bear different side arms in the ligand scaffold. The influence of these substituents has been analyzed. For a detailed description of the catalytic activities, the rate constants kapp and kp were determined using in-situ Raman spectroscopy at a temperature of 150 °C. The polymers produced have molar masses of up to 71 000 g mol−1 and are therefore suitable for a variety of applications. Toxicity measurements carried out for these complexes proved the nontoxicity of the systems. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Optically Induced Avoided Crossing in Graphene
Degenerate states in condensed matter are frequently the cause of unwanted
fluctuations, which prevent the formation of ordered phases and reduce their
functionalities. Removing these degeneracies has been a common theme in
materials design, pursued for example by strain engineering at interfaces.
Here, we explore a non-equilibrium approach to lift degeneracies in solids. We
show that coherent driving of the crystal lattice in bi- and multilayer
graphene, boosts the coupling between two doubly-degenerate modes of E1u and
E2g symmetry, which are virtually uncoupled at equilibrium. New vibronic states
result from anharmonic driving of the E1u mode to large amplitdues, boosting
its coupling to the E2g mode. The vibrational structure of the driven state is
probed with time-resolved Raman scattering, which reveals laser-field dependent
mode splitting and enhanced lifetimes. We expect this phenomenon to be
generally observable in many materials systems, affecting the non-equilibrium
emergent phases in matter.Comment: 13 pages, 4 figure
Using a bio-inspired copper complex to investigate reactive mass transfer around an oxygen bubble rising freely in a thin-gap cell
The present study describes an original colorimetric method to visualize and quantify the local oxygen mass transfer around a rising bubble in reactive media. This method is based on the use of a colorless bio-inspired copper complex, Cu(btmgp)I, specially tailored for the study, which, dissolved in acetonitrile, oxidizes into an orange copper-complex [Cu2O2(btmgp)2]I2. The latter complex, unstable at ambient temperature, decays quite fast into two Cu(II) complexes, leaving a permanent pale-green color as final products. The flow investigated consists in a pure oxygen single bubble rising freely in a confined thin-gap cell (400 × 200 × 1 mm). A wide range of motion regimes for the bubbles are observed as the Archimedes number ranges from and the Reynolds number from . A high-resolution 16-bit sCMOS camera, combined with specific filters, is used to capture images from a region-of-interest of the cell, illuminated by a white LED backlight panel. An ad hoc calibration protocol is developed to correlate the grey-levels from the colored signal to the equivalent oxygen concentrations. This procedure then allows to measure indirectly the amount of oxygen transferred to the liquid phase. The series of images are also treated to identify the bubble motion and properties. Thanks to this method, equivalent oxygen concentration fields, gap-averaged and time-averaged, can be reached with high precision in the far-field wake of the bubbles, enabling thus to deeply characterize the mass transfer mechanisms under reactive conditions in such confined configuration, and to establish a dimensionless representation in terms of Sherwood number versus Peclet number. At last, thanks to the knowledge of the kinetic rate of the reaction and of the diffusion coefficients, the Hatta number and the enhancement factor are estimated, and thus the intrinsic Sherwood numbers; these results demonstrate that the enhancement of the mass transfer by the reactions involved with the copper-complexes is not negligible (almost 12–15%)
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