High-permittivity Solvents Research Articles

High-permittivity Solvents Increase MXene Stability and Stacking Order Enabling Ultraefficient Terahertz Shielding.

2Dtransition metal carbides and nitrides (MXenes) suggest an uncommonly broad combination of important functionalities amongst 2D materials. Nevertheless, MXene suffers from facile oxidation and colloidal instability upon conventional water-based processing, thus limiting applicability. By experiments and theory, It is suggested that for stability and dispersibility, it is critical to select uncommonly high permittivity solvents such as N-methylformamide (NMF) and formamide (FA) (εr =171, 109), unlike the classical solvents characterized by high dipole moment and polarity index. They also allow high MXene stacking order within thin films on carbon nanotube (CNT) substrates, showing very high Terahertz (THz) shielding effectiveness (SE) of 40-60dB at 0.3-1.6 THz in spite of the film thinness <2µm. The stacking order and mesoscopic porosity turn relevant for THz-shielding as characterized by small-angle X-ray scattering (SAXS). The mechanistic understanding of stability and structural order allows guidance for generic MXene applications, in particular in telecommunication, and more generally processing of 2D materials.

Optimization of LIB Electrolyte and Exploration of Novel Compounds via the Molecular Dynamics Method

Due to great interest in the development of electric vehicles and other applications, improving the performances of lithium-ion batteries (LIBs) is crucial. Specifically, components of electrolytes for LIBs should be adequately chosen from hundreds of thousands of candidate compounds. In this study, we aimed to evaluate some physical properties expected for combinations of molecules for electrolytes by microscopic simulations. That is, the viscosity, ionic conductivity, degree of dissociation, diffusion coefficient, and conformation of each molecule were analyzed via molecular dynamics (MD) simulations. We aimed to understand how molecular-sized structures and properties collaboratively affect the behavior of electrolytes. The practical models of molecules we used were ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL), γ-valerolactone (GVL), dimethyl carbonate (DMC), ethyl-methyl carbonate (EMC), diethyl carbonate (DEC), and lithium hexafluorophosphate (LiPF6). Many molecular systems of electrolytes were simulated, in which one molar LiPF6 was mixed into a single or combined solvent. It was found that small solvent molecules diffused with relative ease, and they contributed to the higher ionic conductivity of electrolytes. It was clarified that the diffusion coefficient of lithium (Li) ions is greatly affected by the surrounding solvent molecules. We can conclude that high-permittivity solvents can be selectively coordinated around Li ions, and Li salts are sufficiently dissociated, even when there is only a small content of high-permittivity solvent. Thus, we can confirm solely by MD simulation that one of the better candidates for solvent molecules, formamide (F), will exhibit higher performance than the current solvents.

Molecular dynamics simulation or structure refinement of proteins: are solvent molecules required? A case study using hen lysozyme

In protein simulation or structure refinement based on values of observable quantities measured in (aqueous) solution, solvent (water) molecules may be explicitly treated, omitted, or represented by a potential of mean-solvation-force term, depending on protein coordinates only, in the force field used. These three approaches are compared for hen egg white lysozyme (HEWL). This 129-residue non-spherical protein contains a variety of secondary-structure elements, and ample experimental data are available: 1630 atom–atom Nuclear Overhauser Enhancement (NOE) upper distance bounds, 213 3 J-couplings and 200 S2 order parameters. These data are used to compare the performance of the three approaches. It is found that a molecular dynamics (MD) simulation in explicit water approximates the experimental data much better than stochastic dynamics (SD) simulation in vacuo without or with a solvent-accessible-surface-area (SASA) implicit-solvation term added to the force field. This is due to the missing energetic and entropic contributions and hydrogen-bonding capacities of the water molecules and the missing dielectric screening effect of this high-permittivity solvent. Omission of explicit water molecules leads to compaction of the protein, an increased internal strain, distortion of exposed loop and turn regions and excessive intra-protein hydrogen bonding. As a consequence, the conformation and dynamics of groups on the surface of the protein, which may play a key role in protein–protein interactions or ligand or substrate binding, may be incorrectly modelled. It is thus recommended to include water molecules explicitly in structure refinement of proteins in aqueous solution based on nuclear magnetic resonance (NMR) or other experimentally measured data.

Studies on preparation and formation mechanism of poly(lactide-co-glycolide) microrods via one-step electrospray and an application for drug delivery system

Rod-like microparticles are important drug delivery systems for their large specific surface area and high cell uptake rate. However, complex preparation methods, such as mechanical stretching and cutting after electrospinning restrict applications of rod-like microparticles. In this study, uniformly sized microrods were fabricated via one-step electrospray by using poly(lactide-co-glycolide) (PLGA) solutions with low viscosity, mainly low concentration, and low molecular weights. In contrast to previous results that polymer beads are usually obtained with low-concentration precursor solutions, we prepared 0.5–2.0 μm diameter and 4–20 μm long microrods when the concentration of the solution and molecular weight of the polymer were further decreased. Moreover, the aspect ratio of the microrods decreased significantly after upregulating the loading voltage, adding salt, and using high permittivity solvents. It is suggested that the formation of microrods with an aspect ratio of 4.51·N (N = 1, 2, 3…) was based on the surface wave theory, which was tallied with the experimental data. Furthermore, the doxorubicin(DOX)@PLGA microrods showed higher entrapment efficiency and drug-loading capacity as a drug delivery system compared with those of DOX@PLGA microspheres. Microrods have the potential for a broader range of applications in biomedicine due to the easy preparation process of one-step electrospray.

Electrolyte solvation chemistry for lithium–sulfur batteries with electrolyte-lean conditions

Sparingly solvating electrolytes exhaust free solvents to render a quasi-solid sulfur conversion, while highly solvating electrolytes favor the polysulfide formation and stabilize unique radicals to accelerate redox kinetics. • Sparingly and highly solvating electrolytes in Li–S batteries are reviewed. • Sparingly solvating electrolytes are featured by exhausting free solvents. • Highly solvating electrolytes favor the polysulfide formation. • This Review discusses technical and scientific issues of unique electrolytes. • Electrolyte solvation chemistry perhaps promises energy-dense Li–S batteries. Lithium–sulfur (Li–S) batteries possess overwhelming energy density of 2654 Wh kg −1 , and are considered as the next-generation battery technology for energy demanding applications. Flooded electrolytes are ubiquitously employed in cells to ensure sufficient redox kinetics and preclude the interference of the electrolyte depletion due to side reactions with the lithium metal anode. This strategy is capable of enabling long-lasting, high-capacity and excellent-rate battery performances, but it mask the requirements of practical Li–S batteries, where high-sulfur-loading/content and lean electrolyte are prerequisite to realize the energy-dense Li–S batteries. Sparingly and highly solvating electrolytes have emerged as effective yet simple approaches to decrease the electrolyte/sulfur ratio through altering sulfur species and exerting new reaction pathways. Sparingly solvating electrolytes are characterized by few free solvents to solvate lithium polysulfides, rendering a quasi-solid sulfur conversion and decoupling the reaction mechanisms from electrolyte quantity used in cells; while highly solvating electrolytes adopt high-donicity or high-permittivity solvents and take their advantages of strong solvation ability toward polysulfide intermediates, thereby favoring the polysulfide formation and stabilizing unique radicals, which subsequently accelerate redox kinetics. Both solvation chemistry approaches have their respective features to allow the operation of cells under electrolyte-starved conditions. This Review discusses their unique features and basic physicochemical properties in the working Li–S batteries, presents remaining technical and scientific issues and provides future directions for the electrolyte chemistry to attain high-energy Li–S batteries.

Cation Solvation and Physicochemical Properties of Ca Battery Electrolytes.

Divalent-cation-based batteries are being considered as potential high energy density storage devices. The optimization of electrolytes for these technologies is, however, still largely lacking. Recent demonstration of the feasibility of Ca and Mg plating and stripping in the presence of a passivation layer or an artificial interphase has paved the way for more diverse electrolyte formulations. Here, we exhaustively evaluate several Ca-based electrolytes with different salts, solvents, and concentrations, via measuring physicochemical properties and using vibrational spectroscopy. Some comparisons with Mg- and Li-based electrolytes are made to highlight the unique properties of the Ca2+ cation. The Ca-salt solubility is found to be a major issue, calling for development of new highly dissociative salts. Nonetheless, reasonable salt solubility and dissociation are achieved using bis(trifluoromethanesulfonyl)imide (TFSI), BF4, and triflate anion based electrolytes and high-permittivity solvents, such as ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (gBL), and N,N-dimethylformamide (DMF). The local Ca2+ coordination is concentration-dependent and rather complex, possibly involving bidentate coordination and participation of the nitrogen atom of DMF. The ionicity and the degree of ion-pair formation are both investigated and found to be strongly dependent on the nature of the cation, solvent donicity, and salt concentration. The large ion–ion interaction energies of the contact ion pairs, confirmed by density functional theory (DFT) calculations, are expected to play a major role in the interfacial processes, and thus, we here provide electrolyte design strategies to engineer the cation solvation and possibly improve the power performance of divalent battery systems.

Lithium Fsi-Based Low Ethylene Carbonate Content Electrolyte for High-Power Lib

Among the numerous factors that may influence the charge-discharge rate performance of Li-ion batteries, a desolvation process may be a crucial factor; T. Abe et al. have reported that the Li ion intercalation process into active materials has large activation energies 50 – 60 kJ mol−1in EC-containing conventional organic electrolyte systems and the large activation energy is attributed to the desolvation process of EC molecules from Li ions at an electrode/electrolyte interface [1]. This suggests that the rate-determining process of a charge-discharge reaction is considered the desolvation process of EC molecules from Li ions. Based on the idea described above, the solvation number of EC to a Li ion should be reduced as much as possible to improve charge-discharge rate performance of Li-ion batteries. However, decreasing EC content should decrease the dissociation degree of Li salts and thus the ionic conductivity should decrease. Such a decrease in ionic conductivity would be fatal when we attempt to enhance rate performance of an electrode in a Li-ion battery because the ionic conduction of an electrolyte in a porous structure like an inside structure of positive or negative composite electrodes was found to be much lower than that of the corresponding bulk electrolyte [2]. This finding suggests that decreased ionic conductivity by limited dissociation should strongly impede charge-discharge reaction kineticsinside an electrode, even if the activation energy of a desolvation process is decreased. It is obvious that, therefore, the rate performance of Li ion batteries cannot be improved by just reducing EC content in the usual electrolytes. To avoid this trade-off, we have focused on the interaction between a Li ion and a counter anion in this study. In our previous study on the ionic liquid electrolyte composed of 1-ethyl-3-methylimidazorium bis(fluorosulfonyl)imide (EMImFSI) and Li bis(fluorosulfonyl)imide (LiFSI), we already had known that the interaction between a Li ion and an FSI anion is quite weak [3, 4]. Based on this knowledge, we had expected that LiFSI disassociates sufficiently without usually required high-permittivity solvent conditions. Thus, we prepared LiFSI-based organic electrolytes without EC or with low EC-content and measured their ionic conductivities. As we had expected, these electrolytes showed higher ionic conductivities compared with the case of using conventional Li salts. Furthermore, we observed different electrode/electrolyte interfacial behavior from the conventional electrolytes containing a large amount of EC. This paper mainly reports the electrochemical properties and unusual interfacial behavior of LiFSI-based low-EC-content organic electrolytes and the corresponding superior Li-ion battery performances [5]. We prepare the LiFSI-based low EC content electrolyte (LiFSI / EC:DMC = 1:9) with a low viscosity and high ionic conductivity comparable to conventional LiPF6/ EC:DMC = 1:1 on the basis of our knowledge that the interaction between a Li ion and FSI anion is quite weak. The Li ions in LiFSI / EC:DMC = 1:9 have an unusual solvation state when compared to conventional high EC content electrolyte systems and we considered that the solvation number of EC molecules to a Li ion in LiFSI / EC:DMC = 1:9 is significantly decreased. The graphite half-cell assembled with LiFSI / EC:DMC = 1:9 shows an overwhelmingly small Li ion transfer resistance mainly attributed to a desolvation process. In addition, both the graphite half-cell and the graphite / LiNi1/3Mn1/3Co1/3O2full-cell assembled with LiFSI / EC:DMC = 1:9 show outstanding charge and discharge rate performance when compared to conventional EC:DMC = 1:1 systems. We consider that these results are related to a facile desolvation process attributed to an unusual solvation state of Li ion in LiFSI / EC:DMC = 1:9. Furthermore, the graphite / LiNi1/3Mn1/3Co1/3O2full-cell assembled with LiFSI / EC:DMC = 1:9 shows superior cycle stability compared to the conventional LiPF6/ EC:DMC = 1:1 system, which seems to be attributed to a quite small amount of HF in our LiFSI / EC:DMC = 1:9 system. We will also report electrolyte additives inhibiting corrosion caused by FSI at Al current collector of a cathode.

Cis-to- Trans Isomerization of Azobenzene Derivatives Studied with Transition Path Sampling and Quantum Mechanical/Molecular Mechanical Molecular Dynamics.

Azobenzene-based molecular photoswitches are becoming increasingly important for the development of photoresponsive, functional soft-matter material systems. Upon illumination with light, fast interconversion between a more stable trans and a metastable cis configuration can be established resulting in pronounced changes in conformation, dipole moment or hydrophobicity. A rational design of functional photosensitive molecules with embedded azo moieties requires a thorough understanding of isomerization mechanisms and rates, especially the thermally activated relaxation. For small azo derivatives considered in the gas phase or simple solvents, Eyring's classical transition state theory (TST) approach yields useful predictions for trends in activation energies or corresponding half-life times of the cis isomer. However, TST or improved theories cannot easily be applied when the azo moiety is part of a larger molecular complex or embedded into a heterogeneous environment, where a multitude of possible reaction pathways may exist. In these cases, only the sampling of an ensemble of dynamic reactive trajectories (transition path sampling, TPS) with explicit models of the environment may reveal the nature of the processes involved. In the present work we show how a TPS approach can conveniently be implemented for the phenomenon of relaxation-isomerization of azobenzenes starting with the simple examples of pure azobenzene and a push-pull derivative immersed in a polar (DMSO) and apolar (toluene) solvent. The latter are represented explicitly at a molecular mechanical (MM) and the azo moiety at a quantum mechanical (QM) level. We demonstrate for the push-pull azobenzene that path sampling in combination with the chosen QM/MM scheme produces the expected change in isomerization pathway from inversion to rotation in going from a low to a high permittivity (explicit) solvent model. We discuss the potential of the simulation procedure presented for comparative calculation of reaction rates and an improved understanding of activated states.

Enhancing Self-Assembly in Cellulose Nanocrystal Suspensions Using High-Permittivity Solvents

Helical liquid crystal self-assembly in suspensions of cellulose nanocrystals (CNCs), bioderived nanorods exhibiting excellent mechanical and optical properties, opens attractive routes to sustainable production of advanced functional materials. For convenience, in most studies until now, the CNCs were suspended in water, leaving a knowledge gap concerning the influence of the solvent. Using a novel approach for aggregation-free solvent exchange in CNC suspensions, here we show that protic solvents with a high dielectric permittivity εr significantly speed up self-assembly (from days to hours) at high CNC mass fraction and reduce the concentration dependence of the helix period (variation reducing from more than 30 μm to less than 1 μm). Moreover, our computer simulations indicate that the degree of order at constant CNC content increases with increasing εr, leading to a shorter pitch and a reduced threshold for liquid crystallinity. In low-εr solvents, the onset of long-range orientational order is coupled to kinetic arrest, preventing the formation of a helical superstructure. Our results show that the choice of solvent is a powerful parameter for tuning the behavior of CNC suspensions, enhancing our ability to control the self-assembly and thereby harvesting valuable novel cellulose-based materials.

Solvent Effects for Spectroscopic Properties of Near-Infrared Absorbing Nickel–Dithiolene Complex [Ni(iPr2timdt)2] (iPr2timdt: Monoanion of 1,3-Diisopropylimidazolidine-2,4,5-trithione)

Abstract The near-infrared (NIR) absorption properties of a square-planar nickel–dithiolene complex [Ni(iPr2timdt)2] in various organic solvents have been investigated (iPr2timdt denotes a monoanion of 1,3-diisopropylimidazolidine-2,4,5-trithione). In non-coordinating aprotic organic solvents of smaller relative permittivity (εr &amp;lt; 10) such as dichloromethane (εr = 8.9), the neutral complex [Ni(iPr2timdt)2]0 shows a huge and sharp NIR absorption band at ca. 1000 nm having the molar absorptivity of ε = 6–8 × 104 L mol−1 cm−1. In contrast, in strongly coordinating solvents such as pyridine (Gutmann’s donor number, DN = 33.1), the NIR absorption of [Ni(iPr2timdt)2]0 disappears most probably, owing to the coordination of pyridine molecules onto the axial sites of this square-planar complex. In high relative permittivity solvents such as N,N-dimethylformamide (DMF, εr = 36.71), [Ni(iPr2timdt)2]0 (λmax: ca. 1000 nm) undergoes spontaneous reduction reactions yielding the ionic complexes of [Ni(iPr2timdt)2]− (λmax: ca. 1400 nm) and [Ni(iPr2timdt)2]2− (no NIR peaks), which is indeed reconciled with the results of the spectroelectrochemical measurements. It is stressed that the absorption properties of [Ni(iPr2timdt)2] in the NIR region are sensitive to the solvent properties, and these complex systems serve as NIR probes to report solvent properties.

Libis(fluorosulfonyl)Imide-Based Low EC-Content Electrolyte with Specific Coordination/Solvation Process

In the organic electrolyte for Li-ion batteries, mixed solvents containing a high-permittivity solvent such as ethylene carbonate (EC) and fluoroethylene carbonate (FEC) are essential to form a favorable solid-electrolyte interface (SEI) layer. The mixed solvents should also contain 30 – 50 vol.% high-permittivity solvents in order to obtain high ionic conductivity by sufficient dissociation of Li salts such as LiPF6 and LiBF4. On the other hand, lithium bis(fluorosulfonyl)imide (LiFSI) dissolves easily in a low-permittivity solvent such as dimethyl carbonate (DMC) because LiFSI has very weak interaction between Li+ and FSI-. In the FSI-based systems, therefore, the role of high-permittivity solvents becomes SEI formation only. In this study, we prepared LiFSI-based organic electrolytes with low EC content and found that the Li-ion cells assembled with our electrolytes exhibit excellent charge and discharge rate performance by reduction of charge-transfer resistance associated with a solvation state of EC to Li+. 1.0 mol dm-3 LiFSI dissolved in mixed solvents of EC with DMC (1:9 v/v) was prepared and used as the electrolyte with low EC content (denoted by LiFSI/EC:DMC = 1:9), while 1.0 mol dm-3 LiFSI or LiPF6 dissolved in mixed solvents of EC and DMC (1:1 v/v) were used as reference electrolyte (denoted by LiFSI/EC:DMC = 1:1 and LiPF6/EC:DMC = 1:1, respectively). Graphite or LiNi1/3Mn1/3Co1/3O2 composites containing conductive additive and binder were used as negative and positive electrodes, respectively. The respective mass of active materials in the negative and positive electrodes were ca. 4.5 and 9.5 mg cm-2. We assembled Li/LiNi1/3Mn1/3Co1/3O2, Li/graphite and graphite/LiNi1/3Mn1/3Co1/3O2 cells with each electrolyte and evaluated their battery performances. Table 1 shows the ionic conductivities and viscosities of each electrolyte. LiFSI/EC:DMC = 1:1 shows higher ionic conductivity and slightly lower viscosity than those of the LiPF6/EC:DMC = 1:1. LiFSI/EC:DMC = 1:9 exhibits the lowest ionic conductivity among the tested electrolytes probably because EC content is extremely small in this electrolyte. Nevertheless, the conductivity is still sufficiently high. These characteristics should be ascribed from excellent dissociation ability of LiFSI in spite of low-permittivity conditions. Figure 1 shows the charge-discharge rate performances of Li/graphite cells assembled with each electrolyte. From the ionic conductivities of each electrolyte, it can be expected that the Li/graphite cell containing LiFSI/EC:DMC = 1:1 shows the highest rate performance. In spite of that speculation, however, it is surprising that the Li/graphite cell containing LiFSI/EC:DMC = 1:9 which has the lowest ionic conductivity shows the highest rate performance. In the graphite/LiNi1/3Mn1/3Co1/3O2 cell systems, LiFSI/EC:DMC = 1:9 shows the highest rate performance , which is similar to the Li/graphite cell system. In order to explain these unexpected results, we carried out AC impedance measurement of Li/graphite cells containing each electrolyte. As a result, the Li/graphite cell containing LiFSI/EC:DMC = 1:9 has significantly smaller charge-transfer resistance of the electrode/electrolyte interface when compared to cells containing the other electrolytes. Furthermore, we found that the reduction of charge-transfer resistance is attributed to a specific solvation state of EC to Li+. Raman spectra of each electrolyte show that the solvation number of EC on Li+ reduces significantly in LiFSI/EC:DMC = 1:9. From these results, we consider that the rate performances of the cells containing LiFSI/EC:DMC = 1:9 are improved by the low-energy desolvation process at the Li+ insertion into the electrode by the reduction of the solvation number of EC on Li+.

Switching of the Diastereomer Deposited during the Crystallization of N-[(S)-1-Phenylethyl]-2′-carbamoyl-1,1′-binaphthalene-2-carboxylic Acid: Investigation of the Mechanism of Dielectrically Controlled Resolution

Dielectrically controlled resolution (DCR) has been achieved during the crystallization of (S)-1-phenylethylamides of racemic 1,1'-binaphthalene-2,2'-dicarboxylic acid (RS(a),S)-1. For example, a water well-shaped plot is obtained for the diastereomeric excess (de) of the deposited amide versus the solvent permittivity (ε) for the crystallization of (RS(a),S)-1 from three-component mixed solvents, consisting of 25 vol % of dichloromethane and 75 vol % of varying ratios of two solvents (i.e., an alcohol and either hexane or water). The de value drastically changes within two narrow ε ranges and diastereomerically pure crystals of either (R(a),S)-1 (13.9 ≤ ε ≤ 17.9) or (S(a),S)-1·CH(2)Cl(2) (ε ≤ 11.9 and ε ≥ 21.8) deposit, depending on the solvent permittivity. X-ray crystallographic analyses reveal that the major difference between the crystal structures of (S(a),S)-1 and (R(a),S)-1 is the presence of solvent molecules that fill the spatial voids in the (S(a),S)-1 crystals. The ε-dependence of the chemical shifts of (S(a),S)-1 and (R(a),S)-1 suggests that their aggregation states are similar in the same solvents and change discontinuously at two ε values. The ε-dependence of the C═O stretching vibrations suggests that the lower ε is a transition point where the amide molecules, which aggregate through intermolecular hydrogen bonds in low-permittivity solvents, begin to dissociate. An absorption experiment suggests that dichloromethane is easily incorporated into solvent-free (S(a),S)-1 crystals in high-permittivity solvents. On the basis of these observations, a feasible molecular mechanism is proposed for the present DCR phenomenon.

Insight into the crystal synthesis, activation and application of ZIF-20

The crystallization of the zeolitic imidazolate framework ZIF-20 has been tuned from the point of view of crystal size and aggregation by using rotation and seeding with a previously prepared material. In addition, the activation of ZIF-20 by solvent extraction has been found to be in correlation with the relative permittivity of the solvent. High permittivity solvents (acetone and methanol) extract more guest dimethylformamide but amorphize the structure, while those with low permittivity (n-pentane and chloroform) preserve the crystallinity of ZIF-20. The dispersion in commercial polysulfone of the small synthesized ZIF-20 particles obtained with low aggregation results in an improved O2-selective mixed matrix membrane (O2 permeability and O2/N2 selectivity being 1.0 (±0.0) Barrer and 6.7 (±0.5), respectively).

Planar-Chiral Pillar[5]arene: Chiral Switches Induced by Multiexternal Stimulus of Temperature, Solvents, and Addition of Achiral Guest Molecule

We synthesized chiral-substituents modified pillar[5]arene for the first time. The chiral-substituents modified pillar[5]arene showed planar chirality and interconversion between (pS) and (pR) forms took place quickly. The planar chirality was switched by temperature, solvents, and addition of achiral guest. As the measurement temperature increased, the diastereomeric excess was decreased. The diastereomeric excesses were high in low-permittivity solvents, while a low diastereomeric excess was observed in high-permittivity solvents. Addition of achiral guest induced an increase of negative CD intensities.

Nonadditivity of Polymeric and Charged Surface Interactions: Consequences for Doped Lamellar Phases

We explore theoretically the modifications to the interactions between charged surfaces across an ionic solution caused by the presence of dielectric polymers. Although the chains are neutral, the polymer physics and the electrostatics are coupled; the intrasurface electric fields polarize any low-permittivity species (e.g., polymer) dissolved in a high-permittivity solvent (e.g., water). This coupling enhances the polymer depletion from the surfaces and increases the screening of electrostatic interactions with respect to a model which treats polymeric and electrostatic effects as independent. As a result, the range of the ionic contribution to the osmotic interaction between surfaces is decreased while that of the polymeric contribution is increased. These changes modify the total interaction in a nonadditive manner. Building on the results for parallel surfaces, we investigate the effect of this coupling on the phase behavior of polymer-doped smectics.

Solvent Extraction with Electrokinetic Multicommutation Analysis System

The feasibility of solvent extraction with an electrokinetic flow analysis (EKFA) system should be investigated further because of its non‐aqueous condition. As an example, the pre‐concentration and determination of copper, including on‐line color reaction, solvent extraction, and spectrometric determination were carried out by an electrokinetic multicommutation analysis system in this work. The proposed system consisted of one electroosmotic pump, four solenoid valves which were controlled by a personal computer, and a spectrometric detector. With the electroosmotic pump, sample and reagent solutions were aspirated into the system's color reaction section in small plugs, alternately, and were reacted sufficiently. Then, a plug of chloroform was inserted into the colored zone. The proposed system carried out solvent extraction by moving the sandwiched zone back and forth along its short extraction coil. After phase separation with a T‐shape separator, organic phase was determined in a flow detection cell of the spectrophotometer. The electroosmotic pump is a liquid delivery device with the merits of non‐pulsed and stable flow rate, simple pump structure, high driving efficiency, and facile flow control. Ethanol solution, a relatively high permittivity and innocuous solvent, was adopted as the pump carrier. In this paper, carrier additives were investigated further in order to improve the pump stability and efficiency (3.9 mL min−1 mA−1). The detection limit for copper was 0.03 mg L−1 (K = 3, n = 11) and its recoveries were in the range of 92–96% with a relative standard deviation of 5.2% (n = 3). The proposed method can provide a throughput of 20 samples per hour.

A Raman spectroscopic study of organic electrolyte solutions based on binary solvent systems of ethylene carbonate with low viscosity solvents which dissolve different lithium salts

The ionic structure of organic electrolyte solutions has been investigated, by means of Raman spectroscopy for mixed aprotic solvents that dissolve lithium salts. The solutions consisted of binary solvent systems of a high permittivity solvent (ethylene carbonate, EC) mixed with low viscosity alkyl carbonates (dimethyl carbonate, DMC, and diethyl carbonate, DEC) or a linear alkyl ether (1,2-dimethoxyethane, DME) and of LiCF3SO3, LiPF6 and LiN(C2F5SO2)2 as the solute. The Raman shifts based on the solvents varied with the sort of dissolved lithium salts and their concentration. The ion solvation was estimated from the side-bands of the Raman scattering for the C–O stretch of single bonds of the carbonate groups and for the symmetric ring deformation of EC. The number of EC molecules interacting with the lithium cation (Li+) was higher than that of DMC in a mixed EC+DMC (50:50 by volume) system. The apparent solvation number of Li+ in 1.5 mol dm-3 LiCF3SO3 solution was about 2.8 in EC+DMC, whereas that in 1.5 M LiPF6 solution was about 3.9. Specific solvation of Li+ was distinguished in EC+DME (50:50), where DME predominantly coordinates to Li+. However, it was also confirmed that EC, which has a lower donicity, interacts with Li+ even in the EC+DME system. That is, the solvation number of EC in LiCF3SO3/(EC+DME) remained ca. 1.0 even in high salt concentrations.

Conductometric study of cationic and anionic complexes in propylene carbonate

Conductivity data are used to determine thermodynamic complex formation constants for cases in which both the initial electrolyte and the complexed electrolyte form ion pairs. Using the method described in the text, the complex formation constants of Li+, Na+ and K+ with the crown ether 18-crown-6 and of Li+ with the ligand triphenylphosphine oxide in propylene carbonate have been evaluated from conductance data. The complexation of AgBr in propylene carbonate solutions of n-etrabutylammonium bromide has also been studied by the measurement of molar conductivities. The results of these studies indicate that ion pairing should not be neglected, even in high permittivity solvents such as propylene carbonate, and that the ion pair association constants correlate well with structural studies on cation-crown ether molecular conformations.

Stochastic models of diffusion-controlled ionic reactions-induced spurs. 2. Low-permittivity solvents

The diffusion-controlled recombination of small clusters of ions in low-permittivity solvents is considered. A Monte Carlo simulation technique used previously for high-permittivity solvents is introduced and discussed briefly. The independent reaction times (IRT) simulation method is described, and its implementation for the kinetics of ion clusters is detailed. The IRT approximation is tested against the full Monte Carlo simulation for a variety of random and nonrandom initial configurations and against alternative analytic theories. We find the IRT method to be surprisingly accurate under these stringent conditions.

Stochastic models of diffusion-controlled ionic reactions in radiation-induced spurs. 1. High-permittivity solvents

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStochastic models of diffusion-controlled ionic reactions in radiation-induced spurs. 1. High-permittivity solventsPeter. Clifford, Nicholas J. B. Green, Michael J. Pilling, and Simon M. PimblottCite this: J. Phys. Chem. 1987, 91, 16, 4417–4422Publication Date (Print):July 1, 1987Publication History Published online1 May 2002Published inissue 1 July 1987https://doi.org/10.1021/j100300a043RIGHTS & PERMISSIONSArticle Views142Altmetric-Citations42LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (678 KB) Get e-Alerts