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21.
Conductance measurements for fifteen uni-univalent salts in 2-methylpyridine-N-oxide (2-MPO) were made over the concentration range of 2–120×10–4 mol-dm–3 at 55°C. All conductance data were evaluated by the Lee-Wheaton equation. The results indicate that all of the salts studied are slightly associated in 2-MPO, which is, nevertheless, a reasonably good ionizing solvent compared to other solvents having a similar value for the dielectric constant. The tetraalkylammonium halides are weaker electrolytes than the tetraphenylborate salts in 2-MPO. Ionic limiting molar conductances were obtained by using as a reference electrolyte tris(iso-pentyl)butylammonium tetraphenylborate. Anions appear to be poorly solvated in this solvent but certain cations, particularly Na+ and K+, show evidence of specific ion-solvent interaction.This study was presented, in part, at the 6th Central Regional Meeting of the American Chemical Society, Detroit, Michigan, April 1974. 相似文献
22.
The differential equations and the boundary conditions for the nonequilibrium binary distribution function of an unsymmetrical binary electrolyte are derived from the Ebeling-Falkenhagen continuity equation. The connection between the Onsager reciprocal relation and the binary distribution functions is shown. Further, Feistel's result for thec logc contribution to the conductance is extended to unsymmetrical binary electrolytes. The reason for the difference between Feistel's and Chen'sc logc term is explained, and the significance of Onsager's reciprocal relation for the calculation ofc logc and higher-concentration contributions of the conductance is discussed. 相似文献
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The conductance of potassium iodide has been measured in the solvents ethylene carbonate, water, methyl ethyl ketone, and pairwise mixtures of these solvents at 40°C; and ethylene carbonate-water, tetramethylene sulfone-water, dimethyl sulfoxide-water, tetrahydrofuran-water, ethylene carbonate-tetramethylene sulfone-water, ethylene carbonate-tetramethylene sulfone, and tetrahydrofuran-dimethyl sulfoxide at 25°C. For dielectric constants greater than about 60, the pairing constants KA are in the range 0.3–2.0; no correlation between KA and solvent properties could be established. For lower dielectric constants, KA increases exponentially with decreasing dielectric constant. Addition of a proton, acceptor to water initially decreases KA regardless of whether the dielectric constant of the mixture is higher or lower than that of water, suggesting that ion pairs in water may be stabilized by cage structures. The Walden product Ao is also decreased by the addition of proton acceptors. 相似文献
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By means of a vacuum time-lag method, gas transport properties of apolyimide based on 2, 2- bis (3, 4- decarboxyphenyl ) hexafluoropropane dianhydride (6FDA )and meta- phenylenediamine (mPDA ) have been measured as a function of upstream pres-sure and temperature. The results show that no gas-induced plasticization occurs for thispolyimide in the upstream pressure range from 1 atm to 20atm. The temperature depen-dence of P and D can be described by the Arrhenius equations. The activation energiesof permeation and diffusion were obtained for the gas/polymer pair studied and correlatedwith the size of penetrant gas. 相似文献
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A new family of eight poly(urethane-amide-imide) (PUAI) block copolymers with the same hard block and different soft blocks were synthesized in two steps from a dianhydride monomer containing amide functions (4,4′-methylene-bis(trimellitic anhydride-N-phenylamide)) and α,ω-dihydroxy telechelic oligomers which varied in both chemical structure (polyethers: PEG, PTMG, PPG; polyester: PCL) and molar weight (MW ≅ 600 or 1000 g/mol). The PUAI were obtained in high yields (ranging from 81 to 98 wt%) and with reduced viscosities which varied from 0.36 to 0.84 dL/g (for C = 1 mg/mL in DMF at 25 °C). Their characterization by FTIR and 1H NMR fully confirmed their chemical structure. Their solubility was typically limited to a few wt/vol% even in strong apolar diprotic solvents like DMF and NMP. This particular feature showed the very strong physical cross-linking of their very stiff hard block and enabled to cast membranes capable of withstanding exposure to many common organic solvents. Systematic permeability experiments showed that the PUAI membranes could be used to separate the azeotropic mixture EtOH (20 wt%)/ETBE very easily, with interesting prospects for the purification of ETBE (a fuel octane enhancer used instead of lead derivatives in the European Community). An analysis in terms of structure-property relationships pointed out that the soft block molar weight and polarity were two key parameters for the optimization of selective permeability. The best compromise was obtained with the soft block PEG1000. The corresponding polymer led to performances so far outstanding for polyamideimides with a very high flux of more than 1.1 kg/h m2 for a normalized thickness of 5 μm at 50 °C and a selectivity α = 22.7 in the high range for this kind of separation. 相似文献
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《印度化学会志》2021,98(10):100156
Corona virus disease 2019 (COVID-19) endemic has havoc on the world; the causative virus of the pandemic is SARS CoV-2. Pharmaceutical companies and academic institutes are in continuous efforts to identify anti-viral therapy or vaccines, but the most significant challenge faced is the highly evolving genome of SARS CoV-2, which is imparting evolutionary selective benefits to the virus. To understand the viral mutations, we have retrieved nine hundred and thirty-four samples from different states of India via the GISAID database and analyzed the frequency of all types of point mutation in all structural, non-structural proteins, and accessory factors of SARS CoV-2. Spike glycol protein, nsp3, nsp6, nsp12, N and NS3 were the most evolving proteins. High frequency point mutations were Q496P (nsp2), A380V (nsp4), A994D (nsp3), L37F (nsp6), P323L & A97V (nsp12), Q57H (ns3), D614G (S), P13L (N), R203K (N), G204R (N) and S194L (N). 相似文献
30.
Imide-siloxane block copolymer/silica hybrid membranes: preparation, characterization and gas separation properties 总被引:1,自引:0,他引:1
Ho Bum Park Jang Ki Kim Sang Yong Nam Young Moo Lee 《Journal of membrane science》2003,220(1-2):59-73
Imide-siloxane block copolymer/silica hybrid membranes with covalent bonds were prepared via sol–gel reaction. The structural informations of these hybrid membranes were obtained by using Fourier transform-infrared spectrometry (FT-IR), 29Si nuclear magnetic resonance (29Si NMR), XPS and thermogravimetric analysis (TGA). The gas separation properties of the hybrid membranes were also investigated in terms of organosiloxane (PDMS) or silica content at various temperatures. In the hybrids, the addition of PDMS phase increased the permeabilities of gases such as He, CO2, O2, and N2, indicating that the gas transport occurred mainly through rubbery organic matrix. Meanwhile, the PDMS phase contributed the decreased gas selectivities to nitrogen but the reduction in selectivities was very small in comparison with other siloxane containing polymeric membranes. This might be due to the restriction of chain mobility by the existence of inorganic component such as silica network in the hybrids. Additionally, the increase of silica content in these hybrid membranes considerably retarded the falling-off of gas selectivity at elevated temperature. The increase of silica content in hybrid membranes resulted in well-formed silica networks and hence these inorganic components restricted the plasticization of organic matrix by the thermal segmental motion of organic components, leading to preventing the large decrease of the gas selectivity. 相似文献