Pulsed NMR Techniques Research Articles

Two-Cation Competition in Ionic-Liquid-Modified Electrolytes for Lithium Ion Batteries

It is a common observation that when ionic liquids are added to electrolytes the performances of lithium ion cells become poor, while the thermal safeties of the electrolytes might be improved. In this study, this behavior is investigated based on the kinetics of ionic diffusion. As a model ionic liquid, we chose butyldimethylimidazolium hexafluorophosphate (BDMIPF(6)). The common solvent was propylene carbonate (PC), and lithium hexafluorophosphate (LiPF(6)) was selected as the lithium conducting salt. Ionic diffusion coefficients are estimated by using a pulsed field gradient NMR technique. From a basic study on the model electrolytes (BDMIPF(6) in PC, LiPF(6) in PC, and BDMIPF(6) + LiPF(6) in PC), it was found that the BDMI(+) from BDMIPF(6) shows larger diffusion coefficients than the Li(+) from LiPF(6). However, the anionic (PF(6)(-)) diffusion coefficients present little difference between the model electrolytes. The higher diffusion coefficient of BDMI(+) than that of Li(+) suggests that the poor C-rate performance of lithium ion cells containing ionic liquids as an electrolyte component can be attributed to the two-cation competition between Li(+) and BDMI(+).

Variation of the orientational order parameter in a nematic liquid crystal-COANP-C70 composite structure

Behavior of the orientational order parameter in structures of the nematic liquid crystal (NLC)-organic donor-fullerene type was studied by pulsed 1H NMR techniques. In the NLC sensitized by a fullerenecontaining charge transfer complex, the order parameter at temperatures 10 K below the nematic-isotropic phase transition exhibits an increase and exceeds the value for the initial liquid crystal. This effect is not typical of nonmesogenic additives.

Long-range diffusion in beds of nanoporous particles: pitfalls and potentials

Owing to the recent progress in the area of hardware and software of the pulsed field gradient NMR technique, molecular transport in real-life zeolite systems, such as zeolite beds and particles of formulated fluid catalytic cracking (FCC) catalysts, can be investigated in detail. These studies have revealed a number of important features of molecular transport in zeolites, which are reviewed in the present paper. In particular, the anomalous character of intracrystalline diffusion in MFI-type zeolites, dependence of the tortuosity factor in zeolite beds on diffusion regime and the role of various modes of diffusion in transport limitations arising for catalytic reactions in FCC catalysts will be discussed.

Pulsed NMR for the determination of the nuclear polarization

The polarization in polarized solid targets is usually measured by a continuous wave nuclear magnetic resonance system (CW-NMR). This technique reaches its limits for small and wide signals. The pulsed NMR technique is usually used in nuclear physics and medicine, because of its higher performance and sensitivity compared to the CW-NMR. First tests and linearity measurements of the detection system of our new pulsed NMR will be presented.

Lipid Lateral Diffusion in Ordered and Disordered Phases in Raft Mixtures

Lipid lateral diffusion coefficients in the quarternary system of dioleoylphosphatidylcholine (DOPC), sphingomyelin, cholesterol, and water were determined by the pulsed field gradient NMR technique on macroscopically aligned bilayers. The molar ratio between dioleoylphosphatidylcholine and sphingomyelin was set to 1:1, the cholesterol content was varied between 0 and 45 mol %, the water content was 40 wt %, and the temperature was varied between 293 and 333 K. The diffusion coefficients were separated into fast and slow spectral components by using the CORE method for global analysis of correlated spectral data. A large two-phase region, tentatively assigned to the liquid disordered ( l d) and the liquid ordered ( l o) phases, was present in the phase diagram. The l d phase was enriched in dioleoylphosphatidylcholine and exhibited diffusion coefficients that were about three to five times larger than for the l o phase. Both the diffusion coefficients and the apparent activation energies for the quarternary systems were compatible with earlier reports on ternary phospholipid/cholesterol/water systems. However, in contrast to the latter ternary systems, the exchange of lipids between the l o and the l d phases was slow on the timescale for the diffusion experiment for the quarternary ones. This means that on the millisecond timescale fluid, ordered domains are floating around in a sea of faster diffusing lipids, assigned to consist of mainly dioleoylphosphatidylcholine.

On the 2003 Nobel Prize in medicine or physiology awarded to Paul C. Lauterbur and Sir Peter Mansfield.

On the 2003 Nobel Prize in medicine or physiology awarded to Paul C. Lauterbur and Sir Peter Mansfield.

Water self-diffusion in Chlorella sp. studied by pulse field gradient NMR.

The water self-diffusion behavior in chlorella water suspension was investigated by pulsed field gradient NMR technique. Three types of water was determined, which differs according to the self-diffusion coefficients; bulk water, extracellular and intracellular water. Intracellular and extracellular water self-diffusion were restricted, and the sizes of restriction regions were 3.4 microm and 17 microm, respectively. The water molecular exchange process between these three diffusion regions was investigated. The residence time and exchange rate constant for chlorella cells were obtained. The cell wall permeability determined from the rate constant as 3 x 10(-6) m/s agreed with the permeability 10(-6) m/s obtained from time dependence of intracellular water self-diffusion coefficient. The structural cluster model of chlorella cell is estimated to describe the extracellular water self-diffusion in chlorella water suspension.

Water self-diffusion behavior in yeast cells studied by pulsed field gradient NMR

The water self-diffusion behavior in yeast cell water suspension was investigated by pulsed field gradient NMR techniques. Three types of water were detected, which differ according to the self-diffusion coefficients: bulk water, extracellular and intracellular water. Intracellular and extracellular water self-diffusion was restricted; the sizes of restriction regions were approximately 3 and 15–20 μm, respectively. The smallest restriction size was determined as inner cell size. This size and also cell permeability varied with the growth phase of yeast cell. Cell size increased, but permeability decreased with increasing growth time. The values of cell permeabilities P 1 d obtained from time dependence of water self-diffusion coefficient were in good agreement with the permeabilities obtained from the exchange rate constants P 1 eff. The values of P 1 eff were 7×10 −6, 1.2×10 −6 and 1.6×10 −6 m/s, and P 1 d were 6.3×10 −6, 8.4×10 −7, 1.5×10 −6 m/s for yeast cells incubated for 9 h (exponential growth phase), 24 h (end of exponential growth phase), and 48 h (stationary growth phase), respectively.

The Use of Dimetal Building Blocks in Convergent Syntheses of Large Arrays.

Within the broad field called “supramolecular chemistry,” there is a sector that is based on the use of metal atoms or ions as key elements in promoting the assembly and dictating the main structural features of the supramolecular products. Considerable success has been achieved by using M—M bonded dimetal entities in this role. Metal–metal bonded cationic complexes of the [M2(DAniF)n(MeCN)8–2n](4−n)+ type, where M = Mo or Rh and DAniF is an N,N′-di-p-anisylformamidinate anion, have been used as subunit precursors and then linked by various equatorial and axial bridging groups such as polycarboxylate anions, polypyridyls, and polynitriles. Characterization of the products by single-crystal x-ray diffraction, cyclic voltammetry, differential pulse voltammetry, NMR, and other spectroscopic techniques has revealed the presence of discrete tetranuclear (pairs or loops), hexanuclear (triangles), octanuclear (squares), and dodecanuclear (cages) species and one-, two-, or three-dimensional molecular nanotubes. These compounds display a rich electrochemical behavior that is affected by the nature of the linkers.

Ionic conduction mechanisms of lithium gel polymer electrolytes investigated by the conductivity and diffusion coefficient

Conduction properties of the polymer gel electrolytes of lithium were investigated based on the electrical conductivity and diffusion coefficient using the pulsed gradient spin echo NMR technique. The gel electrolytes prepared by the phase inversion method showed characteristic features in diffusive behavior depending on the kind of immiscible solvent used during the preparation process of the porous polymer membranes. The diffusion coefficients of several kinds of gel were composed of two components that were attributed to the different phases, the trapped solution in the cavities in the membrane and the swollen polymer chains due to the immersed solution. The swollen polymer dominates the high conductivity of this type of gel electrolytes due to the homogenous network appropriate for carrier migration through the chains.

Nonlinear NMR in a superfluid B phase of 3He in aerogel

The properties of liquid 3He in a low-density aerogel preliminarily covered with a few monolayers of 4He were studied by pulsed and nonlinear CW NMR techniques. It was found that an NMR frequency shift from the Larmor value exhibits a sharp increase at a magnetization tilting angle exceeding 104°. Nonlinear CW NMR signals related to the formation of a macroscopic region featuring homogeneous precession of the magnetization (homogeneous precession domain) were observed. The experimental results confirm that the low-temperature superfluid 3He phase in the aerogel is analogous to the B-phase in bulk 3He and indicate that the spin supercurrents play an important role in the spin dynamics of superfluid 3He in aerogel.

Transport Properties of Comb-Type Grafted and Normal-Type N-Isopropylacrylamide Hydrogel

Transport properties of the comb-type grafted and normal-type N-isopropylacrylamide (NIPA) gel are investigated by gel filtration chromatography and a pulsed field gradient NMR technique with known standard probe molecules in terms of molecular weight cutoff and diffusion coefficient in and through the gels, respectively. The incorporation of NIPA grafted chains into NIPA gel makes the effective mesh size smaller and induces the additional friction between the probe molecule and gel network. One may control the maximum mesh size of the NIPA gel and thus the effective diffusivity of a probe molecule within a gel by incorporating grafted chains and by adjusting the temperature.

Comparison of ultrasonic and pulsed NMR techniques for determination of solid fat content

AbstractIn this work an ultrasonic velocity technique was compared to direct pulsed NMR (pNMR) spectroscopy for the determination of the solid fat content (SFC) of anhydrous milk fat (AMF), cocoa butter (CB), and blends of AMF and CB with canola oil (CO) in the range 100 to 70% (w/w). In situ measurements of ultrasonic velocity were carried out during cooling (50–5°C) and heating (5–50°C) of the fat samples, and SFC values were calculated. The SFC were also determined simultaneously by pNMR. Peak melting temperatures determined by DSC were used as an indicator of the polymorphic state of the different fats and fat blends. Estimates of SFC obtained using pNMR and ultrasonic velocimetry did not agree. Our results suggested that ultrasonic velocity was highly dependent on the polymorphic state of the solid fat. Ultrasonic velocity in fat that contained crystals in a more stable polymorphic form was consistently higher than in fat that contained crystals in a less stable polymorphic modification. A high attenuation of the signal was observed in milkfat and CB at lower temperatures, particularly after sitting for 24 h. This high attenuation could be a product of scattering by crystallites or by microscopic air pockets formed upon solidification of the material, or it could be due to high ultrasonic absorption associated with phase transitions. This research highlights some of the problems associated with applying ultrasonics to the determination of SFC.

The use of dimetal building blocks in convergent syntheses of large arrays.

Within the broad field called "supramolecular chemistry," there is a sector that is based on the use of metal atoms or ions as key elements in promoting the assembly and dictating the main structural features of the supramolecular products. Considerable success has been achieved by using MM bonded dimetal entities in this role. Metal-metal bonded cationic complexes of the [M(2)(DAniF)(n)(MeCN)(8-2n)]((4-n)+) type, where M = Mo or Rh and DAniF is an N,N'-di-p-anisylformamidinate anion, have been used as subunit precursors and then linked by various equatorial and axial bridging groups such as polycarboxylate anions, polypyridyls, and polynitriles. Characterization of the products by single-crystal x-ray diffraction, cyclic voltammetry, differential pulse voltammetry, NMR, and other spectroscopic techniques has revealed the presence of discrete tetranuclear (pairs or loops), hexanuclear (triangles), octanuclear (squares), and dodecanuclear (cages) species and one-, two-, or three-dimensional molecular nanotubes. These compounds display a rich electrochemical behavior that is affected by the nature of the linkers.

Interaction of morin with CTMAB: aggregation and location in micellar

The aggregation and location of morin in CTMAB micellar solution was studied by light scattering spectra, electronic absorption spectra and pulsed FT NMR techniques. The difference in the light scattering property of morin with and without CTMAB proved that a large particle of the morin–CTMAB associate formed. Morin has a self-assembly tendency, but the assembly number is not high. With the increase of morin concentration, morin changed from a monomer to dimer. The hyperchromic and bathochromic effect of morin, with the increase in pH value or CTMAB concentration indicated that CTMAB provided a base microenvironment. The changes in the chemical shifts of the individual groups of protons in CTMAB indicated that the solubilization location of morin changes from the inner to the outer of the CTMAB micellar with an increase in morin concentration.

Molecular Diffusion in a Living Network

We report on the diffusion of a surfactant confined in a branched cylindrical “micellar” network, formed by lecithin and small amounts of water in the solvent isooctane. By means of the pulsed field gradient 1H NMR technique, the measured surfactant mean square displacement, 〈z2〉, allows for a detailed investigation on the microstructure of the micellar network. Our results show that the structure depends weakly on the micellar volume fraction, Φ, and strongly on the water-to-lecithin molar ratio, W0. We have studied the lecithin diffusion along two different oil dilution lines, corresponding to different water-to-lecithin molar ratios, 2 and 3. The time window in the diffusion experiments was varied in the range from 50 ms to 1 s. At W0 = 3, a Gaussian diffusion, characterized by a mean square displacement varying linearly with time, was observed for all concentrations and all observation times investigated. Furthermore, the self-diffusion coefficient was found to be independent of the concentration in the micellar volume fraction range studied from Φ = 0.1 to Φ = 0.38. The value of the diffusion coefficient is approximately 1/3 of the value of the lateral diffusion coefficient, Dc. At the second dilution line, W0 = 2, the situation is markedly different. At lower concentrations (Φ < 0.11), we found at shorter times a mean square displacement 〈z2〉 scaling as t1/2 consistent with curvilinear diffusion. For longer times, there was a crossover to a Gaussian diffusion with 〈z2〉 ∝ t. The observation time where there is a crossover from curvilinear to a Gaussian diffusion shifts to shorter times with increasing Φ. At higher concentrations, only a Gaussian diffusion was observed within the experimental time window. The diffusion coefficient evaluated from the Gaussian regime increases linearly with Φ, the value varying from Dc/100 to Dc/20. The high diffusion coefficients evaluated at W0 = 3 clearly indicate that the structure is a branched micellar network where the curvilinear distance along the cylindrical micelles between two branch points is smaller than the persistence length. At W0 = 2, the data can also be interpreted in terms of a branched network, however with a much smaller density of branch points. The branching density increases with increasing Φ. Finally, the measured water diffusion along the two oil dilution lines was found to be Gaussian with a time-independent, single diffusion coefficient. The dominating mechanism for the water diffusion was found to be the motion inside the giant wormlike reverse micelles mediated by an interaggregate exchange with a characteristic time of the order of microseconds.

Diffusion Coefficients in Cold Sulfuric Acid Solution

The diffusion coefficients of dimethyl sulfoxide, dimethyl sulfone, 15N-labeled DNO3, and 17O-labeled D2O in solutions of 0.6−0.8 weight fraction D2SO4 in D2O were studied at temperatures from 248 to 298 K by the pulsed gradient spin-echo NMR technique. Diffusion coefficients for these compounds are reported, and an empirical technique for extrapolating the results to sulfuric acid of stratospheric compositions and temperatures is discussed. The viscosity of 0.7 weight fraction D2SO4 in D2O at temperatures from 248 to 298 K is also reported.

Observation of anomalously fast diffusion in 3He–4He solid solutions near the BCC-HCP transition

The pulsed NMR technique was used to investigate diffusion on the BCC-HCP phase-equilibrium and melting curves of a dilute solution of 3He in 4He. The contributions from all coexisting phases were identified using the spin-echo method. It is established that, along with the contributions from the equilibrium BCC and HCP phases or from bulk liquid (in the melting curve measurements), there is an additional diffusional process that is characterized by an anomalously high diffusion coefficient. It is found that the latter is close to the diffusion coefficient in liquid helium, while the diffusion itself is spatially restricted. The observed effect may be caused by the formation of liquid droplets in the course of the BCC-HCP transition.

T, p-Dependence of intradiffusion in binary fluid mixtures with ammonia as one component

Intradiffusion coefficients Dii were measured for four binary systems with ammonia as one component by the pulsed field gradient NMR technique. The second components are: benzene, acetonitrile, 1-pentanol and methanol. The studies are limited at the low temperature side by the onset of crystallisation. They are extended to a maximum pressure of 200 MPa. The concentration dependence of Dii in the mixtures containing methanol, shows at constant T and p at lower temperatures a pronounced minimum in the Dii s. x curves. This minimum becomes deeper with increasing pressure. This can only be explained by the formation of transient hydrogen bonded networks in which the ammonia molecules participate as donors and acceptors. The data for the ammonia/methanol system are analysed by the mode coupling- and the VTF-models. Both show significant anomalies in the mole fraction range of ammonia x(NH3)≈0.7.

T, p Dependence of intradiffusion in binary fluid mixtures with carbon dioxide as one component

Intradiffusion coefficients Dii were measured by the pulsed field gradient NMR technique for five binary systems with carbon dioxide as one component, the second component being benzene, hydrogen, palmitic acid methyl ester, acetic acid or methanol. The studies are limited for most systems to low temperatures because of the onset of crystallisation. They are extended to a maximum pressure of 200 MPa. The concentration dependence of the hydrogen-containing mixtures shows, at the carbon dioxide rich side of the Dii s. x diagram, a fairly steep increase in diffusivity with hydrogen concentration. The analysis of the methanol/carbon dioxide system is complemented by studies of the hydroxyl proton chemical shift. The x, T, p dependence of the chemical shift is described by a linear association model. These data show clearly that the carbon dioxide molecule does not form any hydrogen bonds with the methanol hydroxyl group.