Search results for "ionic"
showing 10 items of 2016 documents
Stable and Efficient Solid-State Light-Emitting Electrochemical Cells Based on a Series of Hydrophobic Iridium Complexes
2011
Light-emitting electrochemical cells (LECs) based on ionic transition-metal complexes (iTMCs) exhibiting high efficiency, short turn-on time, and long stability have recently been presented. Furthermore, LECs emitting in the full range of the visible spectrum including white light have been reported. However, all these achievements were obtained individually, not simultaneously, using in each case a different iTMC. In this work, device stability is maintained by employing intrinsically stable ionic iridium complexes, while increasing the complex and the device quantum yields for exciton-to-photon conversion. This is done by sequentially modifying the archetype ionic iridium complex [Ir(ppy)…
High-resolution microwave spectroscopy on trapped ion clouds
1994
Ion traps are particular usefully devices for precision spectroscopy on ionic ground states in the microwave domain. Although ultimate precision is achieved only with laser-cooled single ions, in many cases the precision obtained using large uncooled clouds of ions is sufficient for many requirements in atomic physics. The stronger signal in this case makes possible experiments on forbidden transitions or on systems with complex spectra and many substates. Recent examples of laser-microwave double resonance spectra on Pb+ and Eu+ are presented along with attempts to laser-cool a large ion cloud in order to reduce uncertainties from the second-order Doppler effect.
INTERPRETATION OF POTENTIAL INTERMITTENCE TITRATION TECHNIQUE EXPERIMENTS FOR VARIOUS Li-INTERCALATION ELECTRODES
2002
In this paper we compare two different approaches for the calculation of the enhancement factor Wi , based on its definition as the ratio of the chemical and the component diffusion coefficients for species in mixed-conduction electrodes, originated from the “dilute solution” or “lattice gas” models for the ion system. The former approach is only applicable for small changes of the ion concentration while the latter allows one to consider a broad range of intercalation levels. The component diffusion coefficient of lithium ions has been determined for a series of lithium intercalation anodes and cathodes. A new “enhancement factor” for the ion transport has been defined and its relations to…
Enhanced operational stability through interfacial modification by active encapsulation of perovskite solar cells
2020
Encapsulates are, in general, the passive components of any photovoltaic device that provides the required shielding from the externally stimulated degradation. Here we provide comprehensive physical insight depicting a rather non-trivial active nature, in contrast to the supposedly passive, atomic layer deposition (ALD) grown Al2O3 encapsulate layer on the hybrid perovskite [(FA0.83MA0.17)0.95Cs0.05PbI2.5Br0.5] photovoltaic device having the configuration: glass/FTO/SnO2/perovskite/spiro-OMeTAD/Au/(±) Al2O3. By combining various electrical characterization techniques, our experimental observations indicate that the ALD chemistry produces considerable enhancement of the electronic conductiv…
PREPARATION OF OLIGOMERS WITH FUNCTIONAL END GROUPS BY POLYMERIZATION REACTIONS
1973
ABSTRACT The possibilities of preparing oligomers with functional end groups by cationic, anionic and radical polymerization are discussed. Special attention is given to oligomers with two functional end groups (telechelic oligomers). By use of efficient separation techniques, especially GPC, these oligomers can be separated and analyzed. The conclusions that can be drawn from the structure of these oligomers with respect to the elementary processes in polymerization reactions are critically examined.
Optimization of spinning, drawing, and annealing conditions in the production of highly oriented fibers from the polycaprolactam/3.7% LiCl system
1982
A polycaprolactam/3.7% w/w LiCl system, obtained by anionic polymerization of caprolactam directly in the presence of salt, has been employed for the production of highly oriented fibers. More particularly, an optimization of spinning, drawing, and annealing conditions has been performed, finally obtaining fibers which shows very satisfactory mechanical results. Namely, average moduli values up to 12 GPa and strength values up to 1 GPa when fracture is far from clamps, have been observed.
Carbanions on Tap – Living Anionic Polymerization in a Microstructured Reactor
2008
The paper describes the living anionic polymerization of styrenes to homo- and diblock copolymers in continuous flow, using a microstructured mixing set-up ("microreactor"). Reaction times and experimental effort are significantly reduced compared to classical batch methods that often require stringent reaction conditions and strict drying of the apparatus by "break-seal" and "high vacuum" techniques. In continuous flow, residual impurities can be removed by purging the reactor with monomer and initiator solution before polymer samples are collected at the device outlet on a scale of up to 200 g.h -1 . Facile molecular weight adjustment is achieved by variation of the flow rates of initiato…
Macromonomers on the basis of 2-phenyl-2-oxazoline
1988
By initiation of the ring-opening polymerization of 2-phenyl-2-oxazoline (1) with p-iodomethylstyrene a macromonomer with a styrene end-group (2) is obtained. The degree of polymerization was varied between 10 and 16. The radical copolymerization of 2 with styrene is described. 1 forms with methyl triflate a very stable oxazolinium salt which is a good initiator for the bulk polymerization of 1 at temperatures of 50–70°C. It was conclusively proved that under these conditions the polymerization proceeds by a living mechanism. By termination with N, N-dimethylaminopropylmeth-acrylamide a macromonomer (5) was obtained. 5 can be radically homopolymerized. This comb-like polymer 6 has the typic…
Synthesis of block copolymers with poly(methyl methacrylate): P(B-b-MMA), P(EB-b-MMA), P(S-b-B-b-MMA) and P(S-b-EB-b-MMA)
1993
Well-defined diblock copolymers poly(butadiene-b-methyl methacrylate) (=P(B-b-MMA)) and triblock copolymers poly(styrene-b-butadiene-b-methyl methacrylate) (=P(S-b-B-b-MMA)) have been prepared by sequential anionic polymerization in THF. The synthesis of P(B-b-MMA) and P(S-b-B-b-MMA) was most efficient in the presence of lithium alkoxides. By this method side reactions are suppressed and the polymerization can be performed at higher temperatures. The resulting triblock copolymers have narrow molecular weight distribution. The 1,2-PB midblock was quantitatively hydrogenated with tosylhydrazide to enhance thermal stability. Alternatively the hydrogenation can be performed at elevated pressure…
Reductive Decationizable Block Copolymers for Stimuli-Responsive mRNA Delivery
2016
Messenger ribonucleic acids (mRNAs) are considered as promising alternatives for transient gene therapy, but to overcome their poor pharmacokinetic properties, smart carriers are required for cellular uptake and stimuli-responsive release. In this work, a synthetic concept toward reductive decationizable cationic block copolymers for mRNA complexation is introduced. By combination of RAFT block copolymerization with postpolymerization modification, cationic block copolymers are generated with disulfide-linked primary amines. They allow effective polyplex formation with negatively charged mRNA and subsequent release under reductive conditions of the cytoplasm. In first in vitro experiments w…