Search results for "ALK"
showing 10 items of 4314 documents
Review of the Hydrogen Evolution Reaction—A Basic Approach
2021
An increasing emphasis on energy storage has resulted in a surge of R&D efforts into producing catalyst materials for the hydrogen evolution reaction (HER) with emphasis on decreasing the usage of platinum group metals (PGMs). Alkaline water electrolysis holds promise for satisfying future energy storage demands, however the intrinsic potential of this technology is impeded by sluggish reaction kinetics. Here, we summarize the latest efforts within alkaline HER electrocatalyst design, where these efforts are divided between three catalyst design strategies inspired by the three prevailing theories describing the pH-dependence of the HER activity. Modifying the electronic structure of a …
Synthesis and helical supramolecular organization of discotic liquid crystalline dibenzo[hi,st]ovalene
2019
Dibenzo[hi,st]ovalene (DBOV) has emerged as a new polycyclic aromatic hydrocarbon (PAH) with intriguing optical properties with strong red emission. Nevertheless, DBOV derivatives thus far synthesized either had mesityl groups that hinder the pi-pi stacking of the aromatic cores or showed low solubility, and the self-assembly of DBOVs has not been investigated. In this work, two 3,4,5-tris(dodecyloxy)phenyl (TDOP) groups are introduced at the meso-positions of DBOV in order to enhance its solubility without compromising the intermolecular interactions. The obtained DBOV-TDOP forms at elevated temperatures a discotic liquid crystalline phase. Due to pi-pi-stacking interactions as well as loc…
Oxadiazolyl-Pyridinium as Cationic Scaffold for Fluorinated Ionic Liquid Crystals
2021
The synthesis and characterization of a new class of 1,2,4-oxadiazolylpyridinium as a cationic scaffold for fluorinated ionic liquid crystals is herein described. A series of 12 fluorinated heterocyclic salts based on a 1,2,4-oxadiazole moiety, connected through its C(5) or C(3) to an N-alkylpyridinium unit and a perfluoroheptyl chain, differing in the length of the alkyl chain and counterions, has been synthesized. As counterions iodide, bromide and bis(trifluoromethane)sulfonimide have been considered. The synthesis, structure, and liquid crystalline properties of these compounds are discussed on the basis of the tuned structural variables. The thermotropic properties of this series of sa…
Large body size variation is linked to low communication success in tandem running ants
2019
AbstractDiversity in animal groups is often assumed to increase group performance. In insect colonies, genetic, behavioral and morphological variation among workers can improve colony functioning and resilience. However, it has been hypothesized that during communication processes, differences between workers, e.g. in body size, could also have negative effects. Tandem running is a common recruitment strategy in ants and allows a leader to guide a nestmate follower to resources. A substantial proportion of tandem runs fail because leader and follower loose contact. Using the ant Temnothorax nylanderi as a model system, we tested the hypothesis that tandem running success is impaired if lead…
Fabrication and characterization of nanostructured Ni–IrO2 electrodes for water electrolysis
2014
Abstract Nanostructured Ni–IrO2 electrodes were fabricated by electrodeposition in a two-step procedure: first arrays of nickel nanowires (NWs) were electrodeposited within pores of polycarbonate (PC) membranes, then iridium oxide nanoparticles were deposited on the Ni metal after membrane dissolution, for improving the catalytic activity. The aim was to compare performance of these electrodes with traditional ones consisting of Ni film. Different methods of deposition of the IrO2 electrocatalyst were investigated and the effect on electrodes stability and activity is discussed. Despite a low coverage of Ni NWs by the electrocatalyst, results indicate a faster kinetics of O2 evolution in 1 …
TEMPLATE-FREE AND ALKALI-FREE SYNTHESIZED SILICATES WITH MFI-STRUCTURE -A COMPARATIVE STUDY
1993
ABSTRACT Zeolites and gallosilicates with an MFI-structure which were crystallized from inorganic reaction systems and from alkali-free, tetrapropylammonlumbromide (TPABr) containing systems are compared. The strength, nature and distribution of the acidic sites were determined by FTIR-spectroscopy, TPD, electron microprobing, 29 si, 27 Al and 1 H MAS NMR spectroscopy. The influences of the different trivalent elements as well as the strength, type and distribution of the acidic sites on the catalytic performance of the different MFI-silicates are discussed.
Novel triplet of flexor muscles in the posterior tentacles of the snail, Helix pomatia.
2012
The anatomy of three novel flexor muscles in the posterior tentacles of Helix pomatia is described. The muscles originate from the ventral side of the sensory pad and are anchored at different sites in the base of the tentacle stem. The muscles span the tentacle and always take the length of the stem which depends on the rate of tentacle protrusion indicating that the muscles are both contractile and extremely stretchable. The three anchoring points at the base of the stem determine three space axes along which the contraction of a muscle or the synchronous contraction of the muscles can move the tentacle in space.
Metalation and N-alkylation of some polyamides
1981
Totally N-substituted polyamides were synthesized starting from poly(2,4,4-trimethylhexamethylene terephthalamide) by metalation of the amide groups and subsequent reaction with several electrophiles. Polyamides of this structure are not available from terephthalic acid and the corresponding diamines by polycondensation. This N-alkylation reaction can be used for the synthesis of comb-like graft copolymers. The solubilitity and the thermal properties of these polyamide derivatives are described.
Phase separation of symmetric polymer mixtures in a common good solvent in the semidilute concentration regime
1994
Monte Carlo simulations of lattice models of binary (AB) symmetric polymer mixtures (chain lengthsN A=N B=N) in a common good solvent are carried out and the phase diagrams and critical properties of the unmixing transitions are estimated and interpreted in terms of recent theories. Polymers are modeled by self-avoiding walks of lengthN=16, 32 and 64 on the simple cubic lattice. Data for vacancy concentrations of φV=0.6, 0.8 and 0.85 are analyzed. It is shown that forN=16, φV=0.85 no phase separation occurs, down to the lowest temperature, while forN=32, φV=0.85 still phase separation occurs but no longer is complete. Our results are compatible with a scaling theory based on a “renormalizat…
Redetermination of 5,11,17,23-tetra-tert-butyl-25,27-di(ethoxycarbonylmethoxy)-26,28-dihydroxycalix[4]arene chloroform disolvate at low temperature
2003
The title compound, C52H68O8·2CHCl3, previously reported by Ferguson et al. [Supramol. Chem. (1996), 7, 223–228], has been rerefined against new intensity data. The geometric parameters are comparable, as far as they are available. However, the results of the present structure determination are of significantly higher precision.