共查询到20条相似文献,搜索用时 31 毫秒
1.
《Journal of membrane science》2002,196(2):267-277
Physical properties of poly(amic acid) (PAA) casting solutions in N-methyl-2-pyrrolidone (NMP) containing lithium chloride (LiCl) were characterized by viscometry and dynamic light scattering (DLS) and were related to the morphological properties of asymmetric membranes prepared from these solutions. At a fixed polymer concentration, the increase in viscosity of the PAA solutions with increasing LiCl content is mainly determined by the viscosity of the salt–solvent medium, implying that the LiCl–NMP interactions are stronger than those between LiCl and PAA. Because of the strong salt–solvent interactions, complexes between LiCl and NMP are formed. The complexes reduce the solvent power of NMP for PAA inducing polymer aggregation (clustering) and/or transient cross-links in the solutions. Dynamic light scattering results for salt-containing solutions at low PAA concentrations support the existence of these aggregations. Solutions without salt showed a single relaxation, but solutions with LiCl exhibit multiple relaxation modes; two diffusional modes of cooperative and aggregates, and one angle independent transient network mode. The polymer aggregates and transient cross-links form a gel-like structure in the casting solution film and hinder macrovoid formation during phase inversion, resulting in asymmetric membranes with a primarily sponge-like structure. 相似文献
2.
The Raman spectra of saturated solutions of6LiCl and7LiCl have been decomposed into Gaussian components, one of which is a polarized band that occurs at 360 cm–1 when the ion is6Li+ and shifts to 335 cm–1 when the ion is7Li+. Equivalent bands occur in the spectra of saturated solutions of6LiBr and7LiBr at 343 and 320 cm–1, respectively. These bands are assigned to solvent-separated ion aggregates. The Raman spectra of 8.0 and 3.5 m solutions of the isotopic lithium chlorides have been decomposed into five Gaussian components, three of which are assigned to water librations. In addition, there is a polarized band at 440 cm–1 independent of the lithium isotope used, and a depolarized band which occurs at 385 cm–1 in the6LiCl solutions and 360 cm–1 in the7LiCl solutions. We interpret these two additional bands as theA
1 andF
2 stretching modes of Li+ tetrahedrally solvated by water molecules. 相似文献
3.
It is shown that selective measurements of the magnetic dipole—dipole interactions between specific pairs of nuclear spins in glasses of concentrated aqueous electrolytes can provide detailed structural information of relevance to the liquid. The validity of the approach is demonstrated by selective measurements of the inter- and intra-molecular (H2O) proton—proton interactions in LiCl and LiBr solutions at 100 K. For LiCl,4H2O, these measurements are consistent with a short range (≈0.8 nm) distorted sodium chloride structure with Cl? and Li(H2O)+4 as basic units: each Cl? ion is octahedrally coordinated to six OH bonds. For LiCl,RH2O solutions in the composition range 4 <R < 10, the excess H2O is packed interstitially at the interfaces between clusters of LiCl,4H2O. This structure is consistent with various properties of the solution at room temperature. LiBr solutions have similar structures. 相似文献
4.
Jakob Lebon Alexandros Mortis Dr. Cäcilia Maichle-Mössmer Dr. Manfred Manßen Dr. Peter Sirsch Prof. Dr. Reiner Anwander 《Angewandte Chemie (International ed. in English)》2023,62(6):e202214599
Commercially available stock solutions of organolithium reagents are well-implemented tools in organic and organometallic chemistry. However, such solutions are inherently contaminated with lithium halide salts, which can complicate certain synthesis protocols and purification processes. Here, we report the isolation of chloride-free methyllithium employing K[N(SiMe3)2] as a halide-trapping reagent. The influence of distinct LiCl contaminations on the 7Li-NMR chemical shift is examined and their quantification demonstrated. The structural parameters of new chloride-free monomeric methyllithium complex [(Me3TACN)LiCH3], ligated by an azacrown ether, are assessed by comparison with a halide-contaminated variant and monomeric lithium chloride [(Me3TACN)LiCl], further emphasizing the effect of halide impurities. 相似文献
5.
Hilde Verheyden Paul Van Lierde Michael Szwarc Galina Litvinenko Marcel Van Beylen 《Journal of polymer science. Part A, Polymer chemistry》2002,40(13):2148-2157
The addition of lithium chloride (LiCl) to a solution of polystyryllithium (PStLi) in tetrahydropyran (THP) reduces the rate of propagation of PStLi at a low concentration of the latter but accelerates it at higher concentrations of PStLi. Moreover, the addition of LiCl, which is dimeric in ethereal solutions, increases the conductance of PStLi solutions in tetrahydrofuran (THF) and THP to a much greater extent than expected from the separate conductances of PStLi and LiCl, which is itself even less dissociated than PStLi. These phenomena are fully explained by the dual action of LiCl. Below a certain concentration of PStLi, the dissociation, not of LiCl as such, as claimed before, but of its solvated dimer into free Li+ ions and ClLiCl− triple ions provides Li+ ions that repress the ionic dissociation of PStLi by a common ion effect. This, in turn, diminishes the concentration of free polystyryl anions, which are the dominating species responsible for the propagation of PStLi, resulting in retardation. However, at higher concentrations of PStLi, Li+ ions produced by its dissociation are scavenged by the scavenging action of LiCl dimers, producing quintuple cations. This reduces the concentration of free Li+ ions and, therefore, increases the concentration of the reactive free polystyryl anions, resulting in an acceleration of the propagation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2148–2157, 2002 相似文献
6.
Debashis Das 《Journal of solution chemistry》2008,37(7):947-955
Accurate measurements of electrical conductivities and laser Raman spectra of solutions of lithium chloride (LiCl), lithium
bromide (LiBr), lithium tetrafluoroborate (LiBF4) and lithium perchlorate (LiClO4) in tetrahydrofuran are reported. The conductivity data have been analyzed by the Fuoss-Krauss theory, yielding values for
the ion-pair and triple-ion formation constants. The Raman spectra suggest the presence of a new signal of perchlorate ClO4− ions in solution, whereas there is no such evidence for the other investigated anions. The observed processes have been interpreted
by an Eigen multistep mechanism. For each salt, the predominant portion is found to remain in the form of ion pairs, leaving
only a small fraction of triple ions. 相似文献
7.
Quantum-chemical calculations of interaction between lithium chloride and dimethylacetamide (DMAc) and between the polycaproamide model fragment CH3NHCO(CH2)5NHCOCH3 and a lithium chloride solution in DMAc were performed. The software package GAMESS with the MINI basis set was used in the calculations. Models of the solution included 2 LiCl molecules and 8–16 DMAc molecules. All of these models suggest three potential energy minimums corresponding to three stable structures that differ in the relative arrangement of lithium and chloride ions. A decrease in the amount of solvent in the system leads to transition from Li+(DMAc)4Cl- to Li+...Cl-(DMAc)3 and then to the (LiCl)2(DMAc)2 species, which crystallizes to form the 1: 1 crystal solvate. The mechanism of dissolution of polycaproamide in DMAc containing lithium chloride was refined. 相似文献
8.
The lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI) solvent system for cellulose was adopted as a mobile phase of size-exclusion chromatographic (SEC) analysis of cellulose, and the applicability of this system was examined using multi-angle laser light scattering and 13C-NMR analysis. The results indicate that 8% (w/v) LiCl/DMI ID a true solvent for cellulose, and that cellulose molecules dissolving ID 1% (w/v) LiCl/DMI are separated orderly depending on their molecular mass (MM) or root-mean-square (RMS) radius by the SEC system. Practically, no aggregates were detected ID the dilute cellulose/LiCl/DMI solutions. Furthermore, high stability of cellulose/LiCl/DMI solutions has been demonstrated; only a few percent of decline ID average MM was observed even after storage for 6 months at room temperature. Relationships between RMS radius and MM for hardwood bleached kraft pulp ID 1% LiCl/DMI was estimated as the following equation: g0.59, corresponding to a Mark–Houwink–Sakurada exponent of 0.77. 相似文献
9.
Jean Pierre Perchard 《Chemical physics letters》1976,44(1):169-172
Raman spectra of alcohol (methanol, ethanol)—lithium salt (LiCl, LiBr, LiClO4) mixtures were examined. Results on OH stretching bands are presented for saturated solutions at room temperature and for crystals obtained by cooling these solutions. In this second case well defined compounds, of the hydrate type, give rise to very narrow bands, showing that the hydrogen atom positions are ordered. For the CH3OH—LiBr system, isotopic OH/OD dilutions lead to the conclusion of a coupling between four OH identical vibrators, probably surrounding one Br? anion. 相似文献
10.
The concentrations of dissolved silica species in electrolyte solutions were derived from the relative intensities of silica
species, obtained from FAB-MS measurements (fast atom bombardment mass spectrometry), and the total concentration of dissolved
silica. Generally, silica species in aqueous solutions form various complexes with cations such as sodium (Na+) or calcium (Ca2+), and it has been difficult to determine the concentration of each species. From the observed results from FAB-MS, the chemical
species of silica dissolved in lithium chloride (LiCl) and magnesium chloride (MgCl2) solutions do not include complexes with these cations, and thus Li+ and Mg2+ do not replace protons of the silanol groups in silica. Therefore, in LiCl and MgCl2 solutions, all of the simple structures of silicate species can be identified. The concentration of each silica species was
estimated on the basis of its mass spectra peak intensities and the total concentration of silica as determined by colorimetry.
This study yields the concentration of each silica species within small errors, whereas conventional methods (such as 29Si-NMR) have not yielded the concentrations of individual silica species. From these results, dimers and cyclic tetramers
are concluded to be the main species in silica solutions with concentrations of at most 0.1 to 0.2 μmol⋅dm−3. This tendency should also occur in NaCl and CaCl2 solutions, which are major electrolytes in natural waters. 相似文献
11.
应用红外及拉曼光谱研究了不同浓度的四氟硼酸锂在4-乙氧甲基-碳酸乙烯酯溶剂中的离子溶剂化和离子缔合现象。环形变谱带和羰基伸缩振动谱带的分裂,以及骨架环振动谱带的迁移和分裂表明,锂离子与溶剂分子间存在着较强的相互作用,这种相互作用是通过溶剂羰基氧原子实现的。利用光谱拟合技术定量计算了表观溶剂化数。随着电解质锂盐浓度的增加,溶剂化数逐渐由4.32降至1.26。此外,四氟硼酸根v1谱带的分裂表明在高浓度溶液中存在着光谱自由的四氟硼酸根、直接接触离子对和离子对二聚体。 相似文献
12.
A. A. Belyustin A. A. Pronkin I. S. Ivanovskaya V. V. Derii I. V. Murin I. A. Sokolov 《Journal of Analytical Chemistry》2000,55(11):1040-1044
We pioneered the study of the electrode properties of glasses containing 80 and 85 wt % LiF and 20 and 15 wt % A1(PO3)3. LiF-80-based glass electrodes functioned as lithium-selective electrodes in 1-0.0001 M LiCl solutions. Contrary to aliminosilicate
glasses, these glasses responded to the Li+ ion better than to the Na+ ion and were nonselective to the Hi+ ion. This made them promising for the development of sensors for Li+ ions in different solutions. Forward and reverse transitions of these glasses from the hydrogen to the lithium function and
from the lithium to the sodium function are described by the equation of the simple Nikol’skii theory.
Presented at the V All-Russian Conference with the Participation of CIS Countries on Electrochemical Methods of Analysis (EMA-99),
Moscow, December 6–8, 1999. 相似文献
13.
Conductivities of concentrated solutions of lithium chloride in glycerol were measured for concentrations ranging from 0.005 to 1.5 mol.dm?3. The conductivity dependencies were analysed successively using the Debye–Huckel–Onsager limiting law (DHO) at very low concentrations, the Fuoss equation of 1978 up to 0.1 mol.dm?3, the Casteel–Amis empirical equation and the quasi-lattice model (QLM) at moderate and higher concentrations. The molar conductivities at infinite dilution, obtained using DHO and QLM were quite different from each other, because the salt forms contact pairs which were underestimated in the Λ = f(C1/3) in QLM, as it may well be proved by Raman spectroscopy. Besides, the value of Madelung constant suggests that LiCl crystallises face centred cubic (FCC) at higher concentrations. On the basis of Raman spectroscopy analysis of previous lithium salts, we assume that the dissociation coefficient varies slightly with concentration and fraction of paired ion constant, the QLM equation is applied successfully in the concentration range used in this study. The temperature dependency of conductivity was also described using the Vogel–Tamman–Fulcher (VTF) empirical equation where the Arrhenius type was found. The results also suggest that as NaCl, LiCl can be considered as a structure maker electrolyte. 相似文献
14.
Abstract Cellulose carbamate and ester derivatives were synthesized in homogeneous solutions of lithium chloride (LiCl)/N,N-dimemyl-acetamide (DMAc) by the reaction of cellulose with ethyl 4-isocyanatobenzoate and the activated esters of N,N-dimethyl-aminobenzoic acids. Comparative reactions were performed with phenyl isocyanate and the activated ester of benzoic acid. All reactions were followed spectroscopically by FTIR, 1H NMR, and 13C NMR. Degrees of substitution were calculated utilizing UV spectroscopy. The isocyanate reactions are facile allowing controllable degrees of substitution and high yields. By contrast, the activated ester pathway inherently results in lower degrees of substitution and lower yields due in part to undesirable side reactions. 相似文献
15.
In this work conductance measurements were performed on polystyryllithium PStLi in tetrahydrofuran (THF) in the concentration range of 10−3 mol dm−3 at various temperatures between −60°C and 20°C. The comparison with the other alkali salts shows that in these solutions Li+ gives specific interactions with partial electronic charge transfer from the solvent molecules, presumably of the formula LiS4+. A quantitative treatment shows that at 25°C the extrapolated stabilization factor KS is larger than 50000 but rapidly drops for the heavier alkali ions: 3000 for Na+, 200 for K+ and negligible for Cs+. Surprisingly, such a stabilization is not observed for LiCl, although the ionic radii of the anions are quite comparable. The conductances κ at given concentration C of the electrolyte are 100 times smaller. Furthermore the curves of κ2 versus C exhibit in this case an important curvature whereas they are practically linear for PStLi. The absence of specific solvation for LiCl seems thus to be accompanied by the formation of triple ions. Due to the symmetry of the electrolyte the formation of both triple anions ClLiCl− and cations LiClLi+ has to be considered. Moreover, the concentrations of these ions is then always much smaller than that of the neutral dimer LiClLiCl, even if the extent of dimerization of LiCl remains small. The triple ions therefore appear as related to the dissociation of the dimer. This means that through the intermediate formation of the neutral dimer the couples triple ion - counterfoil perpetually exchange an LiCl entity in the course of time: Li+ + ClLiCl−⇋ LiClLiCl ⇋ LiClLi+ + Cl−. Only in the dimer the central LiCl is in possession of the (negative) energy of the insertion bond. In the solution this bond can be attributed neither to ClLiCl− nor to LiClLi+. These entities have to be considered as transient ones during the life-time of which the energy of the insertion bond is transferred to the medium or vice-versa and which possess the energy of the insertion bond only during half of their life-time. The energy of such entities is thus not unambiguously defined in the ensemble at a given time and the ergodic principle does not hold. Such transient species cannot be specifically solvated by the solvent molecules because this would prevent the necessary passage through the dimer form. It is therefore the dimerization of LiCl which opposes itself to the formation of LiS4+ in the THF solutions. Quantitatively the problem can be treated by a thermodynamics based not on ensemble fractions but on time fractions. One considers that a given LiCl can only give solvated ions during a fraction ξC° of the time and that during the remaining fraction it participates in a dissociation process which passes through the formation of non-ergodic triple ions and neutral dimers. (1-ξC°)/ξC° is equal to KaC3/2/[(1 + KS)Kdo]½ where Ka is the non-ergodic equilibrium constant governing the formation of dimers and higher aggregates and Kdo the dissociation constant of LiCl in non-solvated ions. This non-ergodic treatment also allows to describe quantitatively the strange conductometric behaviour of ternary solutions of LiCl and PStLi in THF. The addition of amounts of LiCl in a mole ratio of 7/1 to a given solution of PStLi increases unexpectedly in a very spectacular way the conductivity and provokes the appearance of a non-linear term in the κ2 versus concentration function. In fact this behaviour is due to the replacement of a LiCl entity in the dimers by a PStLi molecule, yielding mixed dimers LiClLiStP. The displaced LiCl molecules are again susceptible of ergodic dissociation and specific solvation of the Li+ ions which originate from this dissociation. Thus for the LiCl entities the time fraction ξC increases. Moreover, at higher concentrations the dissociation of the mixed dimers leads to an important formation of non-ergodic triple anions: Li+ + ClLiStP− ⇋ LiClLiStP ⇋ LiClLi+ + StP− where the entity LiCl constantly jumps in the course of time from an StP− to an Li+ and vice-versa. 相似文献
16.
Chaowei Hao Ying Zhao Yong Zhou Lijuan Zhou Yizhuang Xu Dujin Wang Duanfu Xu 《Journal of Polymer Science.Polymer Physics》2007,45(13):1589-1598
The rheological behavior of poly(vinyl pyrrolidone) (PVP)/N,N‐dimethylformamide (DMF) solutions containing metal chlorides (LiCl, CaCl2, and CoCl2) were investigated, and the results showed that the nature of the metal ions and their concentration had an obvious effect on the steady‐state rheological behavior of PVP–DMF solutions with different molecular weights. The apparent viscosity of the PVP–DMF solutions increased with an increasing metal‐ion concentration, and the viscosity increment was dependent on the metal‐ion variety. For a CaCl2‐containing PVP–DMF solution, for example, the critical shear rate at the onset of shear thinning became smaller with increasing CaCl2 concentration. It was believed that multiple interactions among metal ions, carbonyl groups of PVP, and amide groups in DMF determined the solution properties of these complex fluids; therefore, 13C NMR spectroscopy was used to detect the interactions in systems of PVP–CaCl2–DMF and PVP–LiCl–DMF solutions. NMR data showed that there were obvious interactions between the metal ions and the carbonyl groups of the PVP segments in the DMF solutions. Furthermore, IR spectra of the PVP/metal chloride composites demonstrated that the interaction between the metal ions and carbonyl groups in the PVP unit occurred and that the PVP chain underwent conformational variations with the metal‐ion concentration. DSC results indicated that the glass transition temperatures of the PVP/metal chloride composites increased with the addition of metal ions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1589–1598, 2007 相似文献
17.
Hongwei Qiao Helin Luan Zhiming Zhou Lixue Bi Wen Yao Jimei Li Chang Chen 《Journal of Molecular Structure》2008,885(1-3):89-96
Solvation and association interactions in solutions of LiBF4/DMCC (DMCC for N,N-dimethylcarbamoyl chloride) and LiBF4/DMCC–DME (DME for 1,2-dimethoxyethane) have been studied as a function of concentration of lithium tetrafluoroborate by infrared and Raman spectroscopy. Strong interactions between Li+ and solvent molecules or BF4− anions are observed. The apparent solvation numbers of Li+ in LiBF4/DMCC solutions were deduced. Band-fitting to the B–F stretching band of BF4− anion permits detailed assess of the ion pairing. Based on the calculations of density function theory, optimal structures of Li+(DMCC)n (n = 1–3) were suggested. It is found that the lithium ion was preferentially solvated by DME in DMCC–DME binary solvents. This finding is supported by quantum chemistry calculations. 相似文献
18.
M. L. P. Reddy 《Journal of Chemical Sciences》1991,103(2):95-98
The extraction behaviour of Cu(II) from hydrochloric acid and lithium chloride solutions with di-n-pentyl sulphoxide (DPSO) and di-n-octyl sulphoxide (DOSO) has been investigated over a wide range of conditions. At a given strength of the extradant, the
extraction increases with increase in HCl and LiCl concentrations. The extraction of the metal also increases with increase
in extractant concentration at constant [HCl] or [LiCl]. The species extracted would appear to be CuCl2·2DPSO/2DOSO and CuCl
4
2−
·2DPSO. The extraction of the metal decreases with increase in initial aqueous metal concentration and also with increase
in temperature. The extraction also depends on the nature of the diluent employed. 相似文献
19.
《Journal of mass spectrometry : JMS》2018,53(8):705-716
The dissolution mechanism of oligosaccharides in N,N‐dimethylacetamide/lithium chloride (DMAc/LiCl), a solvent used for cellulose dissolution, and the capabilities of low‐energy collision‐induced dissociation (low‐energy CID), collision‐induced dissociation (CID), and higher energy collision dissociation (HCD) for structural analysis of carbohydrates were investigated. Comparing the spectra obtained using 3 techniques shows that, generally, when working with monolithiated sugars, CID spectra provide more structurally informative fragments, and glycosidic bond cleavage is the main pathway. However, when working with dilithiated sugars, HCD spectra can be more informative providing predominately cross‐ring cleavage fragments. This is because HCD is a nonresonant activation technique, and it allows a higher amount of energy to be deposited in a short time, giving access to more endothermic decomposition pathways as well as consecutive fragmentations. The difference in preferred dissociation pathways of monolithiated and dilithiated sugars indicates that the presence of the second lithium strongly influences the relative rate constants for cross‐ring cleavages vs glycosidic bond cleavages, and disfavors the latter. Regarding the dissolution mechanism of sugars in DMAc/LiCl, CID and HCD experiments on dilithiated and trilithiated sugars reveal that intensities of product ions containing 2 Li+ or 3 Li+, respectively, are higher than those bearing only 1 Li+. In addition, comparing the fragmentation spectra (both HCD and CID) of LiCl‐adducted lithiated sugar and NaCl‐adducted sodiated sugar shows that while, in the latter case, loss of NaCl is dominant, in the former case, loss of HCl occurs preferentially. The compiled evidence implies that there is a strong and direct interaction between lithium and the saccharide during the dissolution process in the DMAc/LiCl solvent system. 相似文献
20.
The hydration process of lithium iodide, lithium bromide, lithium chloride and lithium nitrate in water was analyzed quantitatively by applying multivariate curve resolution alternating least squares (MCR-ALS) to their near infrared spectra recorded between 850 nm and 1100 nm. The experiments were carried out using solutions with a salt mass fraction between 0% and 72% for lithium bromide, between 0% and 67% for lithium nitrate and between 0% and 62% for lithium chloride and lithium iodide at 323.15 K, 333.15 K, 343.15 K and 353.15 K, respectively. Three factors were determined for lithium bromide and lithium iodide and two factors for the lithium chloride and lithium nitrate by singular value decomposition (SVD) of their spectral data matrices. These factors are associated with various chemical environments in which there are aqueous clusters containing the ions of the salts and non-coordinated water molecules. Spectra and concentration profiles of non-coordinated water and cluster aqueous were retrieved by MCR-ALS. The amount of water involved in the process of hydration of the various salts was quantified. The results show that the water absorption capacity increases in the following order LiI < LiBr < LiNO3 < LiCl. The salt concentration at which there is no free water in the medium was calculated at each one of the temperatures considered. The values ranged between 62.6 and 65.1% for LiBr, 45.5–48.3% for LiCl, 60.4–61.2% for LiI and 60.3–63.7% for LiNO3. These values are an initial approach to determining the concentration as from which crystal formation is favored. 相似文献