Spin-echo Nuclear Magnetic Resonance Research Articles

Investigating the Differences between the in-Situ Galvanostatic Test and Ex-Situ Fenton Test on Nafion Membranes for PEM Water Electrolysis

Perfluorinated sulfonic acid (PFSA) ionomer membranes (e.g Nafion) are widely employed as the benchmark materials for the electrolyte membranes in PEM water electrolysis (PEMWE). It is broadly acknowledged that the state of health of PFSA membranes is detrimentally impacted by the chemical degradation occurring during operation of PEMWE. The cross-over gases interacting with the catalytic surface lead to the generation of hydrogen peroxide. This compound can undergo homolytic cleavage or, in the presence of ferrous salts, yield reactive oxygen species such as hydroperoxyl (HOO.) and hydroxyl (HO.) radicals. These radicals attack the ionomer subsequently leading to chain scission, unzipping and loss of functional groups and release of HF in the effluent water. However, the degree of degradation differs when exposed to ex-situ conditions compared to real proton exchange membrane (PEM) water electrolysis conditions.This work depicts a methodical investigation of degradation of catalyst coated Nafion membranes (CCM) using a Fenton's accelerated aging experiment and in-situ test. In the Fenton's approach, the durability of Nafion 117 and catalyst coated Nafion membrane with counter ions such as ferrous ions against H2O2 was explored as a degradation factor of polymer electrolyte water electrolyser. CCMs were submerged to a solution containing ferrous ions and peroxide. Accelerated aging experiments were conducted over a period of 3-7 days. An in-situ ageing test has been performed on a MEA with and without the presence of Ferrous ions by applying galvanostatic pulses for 7 days. Experimental confirmation of degradation mechanisms has been obtained by post-mortem analysis of the MEA using microscopy and chemical analysis and mechanical investigation. To quantify the effect of water activity in Nafion and CCM chemical structure on both water diffusion and interfacial transport, pulse field gradient spin echo nuclear magnetic resonance (PFGSE-NMR) technique has been employed. Morphological characteristics before and after aging tests were also investigated. Comparative estimation of the fluoride release rate in case of both in-situ and ex-situ test was also performed. This work offers a comprehensive dataset comparing the performance of degraded membranes both in situ and ex situ.

Comparative Analysis of Degradation of Pristine Nafion and Catalyst Coated Membrane Subjected to Ex-Situ Fenton's Test Approach

Polyfluorinated sulfonic –acid ionomer membranes (e.g Nafion) are extensively used today as the benchmark materials for the electrolyte membrane in PEM water electrolysis. It is broadly accepted that the state of the health of PFSA membranes are adversely impacted by the chemical degradation occured during operation of PEMWE. The crossover gases on the catalytic surface generate Hydrogen Peroxide which is homolytically or in the presence of ferrous salts produce reactive oxygen species like hydroperoxyl (HO.) and hydroxyl (HO.) radicals. These radicals attack the ionomer subsequently leading to chain scission, unzipping and loss of functional groups and release of HF in the effluent water.Other than Fe3+, several transition metal ions Cu2+, Ni2+, Ti3+, Cu+, can poison the membrane significantly. The fact that membrane degradation is accelerated owing to introduction of ferrous ions is fervently implemented in ex-situ degradation tests (known as Fentons tests) to evaluate the durability of membrane materials.This work depicts a systematic investigation of degradation of pristine Nafion and catalyst coated Nafion membrane using a Fentons accelerated aging experiment. The durability of Nafion 117 and catalyst coated Nafion membrane with various counter ions against H2O2 was explored as a degradation factor of polymer electrolyte water electrolyser. Two distinct variations of the experiments were compared : (1) Nafion and CCM were dipped in only hydrogen peroxide solution, (2) Nafion and CCM were exposed to a solution containing ferrous ions and peroxide. Accelerated aging experiments were conducted over 3-7 days. The difference in degradation phenomena with and without Fe ions were evaluated in terms of the fluoride ion release. For both cases, to quantify the effect of water activity in Nafion and CCM chemical structure on both water diffusion and interfacial transport, pulse field gradient spin echo nuclear magnetic resonance (PFGSE-NMR) technique has been employed. Furthermore the equivalent weight of the Nafion and CCM can vary in presence of aforementioned chemical stressors which can be accurately quantitatively studied by confocal Raman spectroscopy. Morphological characteristic before and after aging test was also investigated. Role of H2O2 and ferous ion in mechanical behaviour of Nafion and CCM were also analyzed. The same experiment was repeated for different transition metal ions. This work sheds light on decomposition mechanism of Nafion and CCM in more detail.

Sensitivity-Enhanced Spin Echo Nuclear Magnetic Resonance Pulse Sequence for Quantitative Polymer Characterizations with a Nuclear Magnetic Resonance Cryoprobe

Sensitivity-Enhanced Spin Echo Nuclear Magnetic Resonance Pulse Sequence for Quantitative Polymer Characterizations with a Nuclear Magnetic Resonance Cryoprobe

Self-diffusion of aromatic compounds in the carbon tetrachloride – acetone binary system. NMR experiment and MD simulation

In this work, we studied the influence of the structure of molecules of aromatic compounds (methylparaben (MP), propylparaben (PP), syringic acid (SA), gallic acid (GA), protocatechualdehide (PAL), p-coumaric acid (p-CA), and caffeic acid (CA)) on their molecular association and self-diffusion in the binary carbon tetrachloride – acetone solvent. The self-diffusion coefficients of PAL, SA, and GA in the binary carbon tetrachloride – acetone‑d6 solvent were measured by the pulsed gradient spin-echo nuclear magnetic resonance (PGSE NMR) method at temperatures of 288, 298, and 308 K. The data obtained at 298 K were also compared with the data on the self-diffusion coefficients of MP, PP, CFA, and p-CA in the binary solvent available in the literature. According to the presented data, the self-diffusion coefficients of all the substances under consideration become greater with an increase in the acetone‑d6 concentration and decrease in the MP > PAL > PP > p-CA > SA > CA > GA series of compounds. Quantitative assessment of the degree of influence of molecular association on solute self-diffusion was carried out within the framework of a method based on the ratio of the self-diffusion coefficient of a solute to the self-diffusion coefficient of its monomers. The study shows that the degree of influence of molecular association of the solute on its self-diffusion is determined by the number and type of active functional groups in the structure of the solute molecules (MP < PP < PAL < SA < p-CA < CA < GA), but does not depend on the composition of the binary solvent. According to the results of molecular dynamics (MD) simulation, this effect correlates with the increase in the degree of self-association of solutes and decrease in the degree of solute – acetone heteroassociation observed when the carbon tetrachloride concentration becomes higher. This effect is also responsible for the similar concentration dependencies of the self-diffusion coefficients of active and inert compounds.

Water Diffusion and Uptake in Injectable ETTMP/PEGDA Hydrogels.

Differential scanning calorimetry (DSC) and pulsed field gradient spin echo nuclear magnetic resonance (PFGSE NMR) were used to characterize water in hydrogels of ethoxylated trimethylolpropane tri-3-mercaptopropionate (ETTMP) and poly(ethylene glycol) diacrylate (PEGDA). Freezable and nonfreezable water were quantified using DSC; water diffusion coefficients were measured using PFGSE NMR. No freezable water (free or intermediate) was detected from DSC for hydrogels of 0.68 and greater polymer mass fractions. Water diffusion coefficients, from NMR, decreased with increasing polymer content and were assumed to be weighted averages of free and bound water contributions. Both techniques showed decreasing ratios of bound or nonfreezable water mass per polymer mass with increasing polymer content. Swelling studies were used to quantify the equilibrium water content (EWC) to determine which compositions would swell or deswell when placed in the body. At 30 and 37 °C, fully cured, non-degraded ETTMP/PEGDA hydrogels at polymer mass fractions of 0.25 and 0.375, respectively, were shown to be at EWC.

The structure and dynamics of bottlebrushes: Simulation and experimental studies combined

Bottlebrushes are complex macromolecular structures composed of polymer chains densely tethered to another polymer chain via a stable covalent bond linkage. Although numerous experimental techniques have been successfully applied for the characterization of bottlebrush polymers, some parameters still cannot be determined. Herein new simulation method using a dedicated machine was used to confront its applicability for complex macromolecules simulations. The bottlebrushes were synthesized by atom transfer radical polymerization (ATRP) with varied degree of polymerization (N) of the side chains, poly(methyl methacrylate) (PMMA). Poly(2-(2-bromoisobutyryloxy)ethyl methacrylate) (PBiBEM) was used as macroinitiator with a degree of polymerization Nbb = 102. Degree of polymerization of side chains (Nsc) changed from 28 to 113. The bottlebrushes were characterized by Gel Permeation Chromatography – Multiangle Laser Light Scattering (GPC-MALLS), Pulsed-field Gradient Spin Echo Nuclear Magnetic Resonance (PGSE NMR), and combined Static and Dynamic Light Scattering methods (SLS-DLS). A novel calculation strategy via the Monte Carlo-class Dynamic Lattice Liquid (DLL) algorithm executed on a dedicated machine ARUZ was applied for theoretical studies. The experimental values concerning the scaling behavior of polymer size and dynamics were compared and confronted with simulation results.

Structural rearrangements during sub-Tg relaxation and nucleation in lithium disilicate glass revealed by a solid-state NMR and MD strategy

Structural rearrangements taking place during relaxation and crystal nucleation in lithium-disilicate (LS2) glass have been investigated by a comprehensive set of solid-state nuclear magnetic resonance (NMR) experiments, supported by molecular dynamics (MD) simulations. Samples were subjected to heat treatments at 435 °C, i.e., 20 K below the laboratory glass transition temperature (Tg). Raman and NMR data indicate that under these conditions both relaxation and nucleation occur without detectable changes in the network former unit distribution of the glassy silicon-oxide network. Instead, relaxation of the frozen supercooled melt and nucleation of LS2 crystals occur principally in terms of a changing lithium local environment: 7Li spin-echo decay NMR indicates average Li-Li distances, characterized by homonuclear dipolar second-moment measurements, are reduced after very short heat treatments and approach those found in the isochemical crystal. This finding is supported by molecular dynamics (MD) simulations predicting a dependence of the Li+ ion distribution on the melt-cooling rate. In addition, the structural reorganization also impacts the distribution of electric field gradients as detected by 7Li satellite transition NMR spectroscopy. Finally, crystal nucleation becomes most evident by the appearance of minor amounts of sharp 29Si MAS resonances and a significant change in the 7Li NMR satellite transitions, as visualized by difference spectroscopy. This study defines a new NMR strategy, generally applicable for investigating the structural relaxation process accompanying the internal crystallization of ion-conducting frozen supercooled melts containing suitable NMR active nuclear probes (7Li, 23Na, 133Cs, etc.).

Self-diffusion and molecular association in the binary systems dimethyl sulfoxide – chloroform and acetone – chloroform

The self-diffusion of components of such binary mixtures as dimethyl sulfoxide (DMSO) – chloroform and acetone – chloroform has been investigated by pulsed gradient spin-echo nuclear magnetic resonance (PGSE NMR) method and molecular dynamics (MD) simulation at ambient conditions. The self-diffusion coefficients obtained by the experimental and theoretical methods are well agreed with each other. Detailed analysis of structural characteristics (fraction of molecules with i hydrogen bonds, the average number of hydrogen bonds), as well as interaction energy in hydrogen-bonded complexes of DMSO – DMSO, DMSO – chloroform, acetone – acetone, acetone – chloroform made it possible to estimate the influence of the self- and heteroassociation on the self-diffusion of the mixture components. A set of methods showed that it is necessary to take into account not only heteroassociates with a composition of 1:1 just like acetone – chloroform mixture for sufficient approximation of the experimental data for DMSO – chloroform mixture. It has been established that for cosolvents (DMSO and acetone) with a similar molecular structure, a different behavior of concentration dependences of the self-diffusion coefficients in binary systems is connected with the features of self-association and heteroassociation.

Investigation of the aggregation behaviour of the anionic surfactant sodium dodecyl sulfate in ionic liquids 1-allyl-3-methylimidazolium chloride and 1-Ethyl-3-methylimidazolium diethyl phosphate

We investigated the aggregation behaviour of the anionic surfactant sodium dodecyl sulfate (SDS) in 1-allyl-3-methylimidazolium chloride (AMIMCl) ionic liquid at three temperatures 323 K, 333 K and 343 K using 1H Nuclear Magnetic Resonance (NMR) chemical shift and Pulsed-Field Gradient (PFG) spin-echo NMR self-diffusion measurements. Chemical shifts of SDS protons and diffusion coefficients of SDS as a function of the surfactant concentration have breakpoints, which indicate an onset of the surfactant micellisation. We estimated the critical micelle concentration (cmc) with high accuracy from SDS methyl protons' chemical shifts and the micelles' average aggregation number from diffusion coefficients. The formation of micelles does not influence the diffusion and chemical shifts of AMIMCl.We determined water concentration in the samples from the NMR spectra. We did not find evidence that water affects the aggregation process since water content practically does not influence the SDS protons' chemical shifts and diffusion coefficients. However, water appears to influence the diffusion and chemical shifts of AMIMCl.We also investigated the behaviour of SDS in 1-Ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) hydrophilic ionic liquid. The value of the Gordon parameter of EMIMDEP indicates that it does not possess the ability to support the self-assembly of amphiphiles. Within this work, we treat the system SDS/EMIMDEP as a reference one.SDS forms a lamellar phase in AMIMCl at high concentration, as revealed by Small Angle X-ray Scattering (SAXS) and Polarised Optical Microscopy (POM) investigations. At about 358 K, a transition from the lamellar phase to the isotropic liquid phase occurs. No other liquid-crystalline phase in this system was determined.

Using NMR to Test Molecular Mobility during a Chemical Reaction.

We evaluate critically the use of pulsed gradient spin-echo nuclear magnetic resonance to measure molecular mobility during chemical reactions. With raw NMR spectra available in a public depository, we confirm the boosted mobility during the click chemical reaction (Wang et al. Science 2020 369, 537-541) regardless of the order of magnetic field gradient (linearly increasing, linearly decreasing, random sequence). We also confirm boosted mobility for the Diels-Alder chemical reaction. The conceptual advantage of the former chemical system is that a constant reaction rate implies a constant catalyst concentration, whereas that of the latter is the absence of a paramagnetic catalyst, precluding paramagnetism as an objection to the measurements. The data and discussion in this paper show the reliability of experiments when one avoids convection, allows decay of nuclear spin magnetization between successive pulses and recovery of its intensity between gradients, and satisfies quasi-steady state during the time window to acquire each datum. Especially important is to make comparisons on the time scale of the actual chemical reaction kinetics. We discuss possible sources of mistaken conclusions that are desirable to avoid.

Proton conduction in hydronium solvate ionic liquids affected by ligand shape.

We investigated the ligand dependence of the proton conduction of hydronium solvate ionic liquids (ILs), consisting of a hydronium ion (H3O+), polyether ligands, and a bis[(trifluoromethyl)sulfonyl]amide anion (Tf2N-; Tf = CF3SO2). The ligands were changed from previously reported 18-crown-6 (18C6) to other cyclic or acyclic polyethers, namely, dicyclohexano-18-crown-6 (Dh18C6), benzo-18-crown-6 (B18C6) and pentaethylene glycol dimethyl ether (G5). Pulsed-field gradient spin echo nuclear magnetic resonance results revealed that the protons of H3O+ move faster than those of cyclic 18C6-based ligands but as fast as those of acyclic G5 ligands. Based on these results and density functional theory calculations, we propose that the coordination of a cyclic ether ligand to the H3O+ ion is essential for fast proton conduction in hydronium solvate ILs. Our results attract special interest for many electro- and bio-chemical applications such as electrolyte systems for fuel cells and artificial ion channels for biological cells.

Influence of the number and type of functional groups on self-diffusion of some aromatic compounds in acetone: Nuclear magnetic resonance and molecular dynamics simulations

Self-diffusion of parabens (methylparaben and propylparaben), phenolic acids (syringic and gallic acids) and their derivative (protocatechualdehyde), hydroxycinnamic acids (caffeic, ferulic, sinapic, and p-coumaric acids), and tetramethylsilane in acetone has been investigated by the pulsed gradient spin-echo nuclear magnetic resonance (PGSE NMR) method and molecular dynamics simulation in ambient conditions. The self-diffusion coefficients obtained by the experimental and theoretical methods are in good agreement with each other. A detailed analysis of the average number of solute – acetone hydrogen bonds has made it possible to trace the influence of the molecular heteroassociation on the self-diffusion of the aromatic compounds. The degree of influence of solute – acetone molecular association on the solute self-diffusion defined as the ratio of the solute self-diffusion coefficient to the self-diffusion coefficient of its monomer has been calculated using the Stokes-Einstein equation. It has been found that for a number of aromatic compounds with the same type and number of functional groups, the parameter expressing the degree of influence of molecular association has similar values. This fact has allowed us to calculate the self-diffusion coefficients of the compounds in the given series at a known self-diffusion coefficient value of one of the series members.

Diffusion Spectrum of Polymer Melt Measured by Varying Magnetic Field Gradient Pulse Width in PGSE NMR.

The translational motion of polymers is a complex process and has a big impact on polymer structure and chemical reactivity. The process can be described by the segment velocity autocorrelation function or its diffusion spectrum, which exhibit several characteristic features depending on the observational time scale—from the Brownian delta function on a large time scale, to complex details in a very short range. Several stepwise, more-complex models of translational dynamics thus exist—from the Rouse regime over reptation motion to a combination of reptation and tube-Rouse motion. Accordingly, different methods of measurement are applicable, from neutron scattering for very short times to optical methods for very long times. In the intermediate regime, nuclear magnetic resonance (NMR) is applicable—for microseconds, relaxometry, and for milliseconds, diffusometry. We used a variation of the established diffusometric method of pulsed gradient spin-echo NMR to measure the diffusion spectrum of a linear polyethylene melt by varying the gradient pulse width. We were able to determine the characteristic relaxation time of the first mode of the tube-Rouse motion. This result is a deviation from a Rouse model of polymer chain displacement at the crossover from a square-root to linear time dependence, indicating a new long-term diffusion regime in which the dynamics of the tube are also described by the Rouse model.

Unravelling the role of a green rejuvenator agent in contrasting the aging effect on bitumen: A dynamics rheology, nuclear magnetic relaxometry and self-diffusion study

This paper evaluated the potentialities of a green and biocompatible rejuvenator agent (HR) in conferring an appreciable resistance against the effects caused by artificial aging on a given bitumen. Both neat and aged bitumens were analyzed and compared to analogous samples modified with HR. Control samples containing a vegetable oil as softening agent were also tested for comparison. The tested samples were subjected to a second aging cycle. Structural differences between the samples were carried out through an inverse Laplace transform of the NMR spin-echo decay (T2) and self-diffusion measurements by pulsed gradient spin echo nuclear magnetic resonance (PGSE-NMR) spectroscopy. In addition, dynamic rheological analyses were conducted to determine the dependence of the gel-sol transition temperature on both the type of additive and ageing process. The present study clearly highlighted the fact that artificial ageing, realized here by the rolling thin film oven test (RTFOT) and the pressure ageing vessel (PAV) test, induced important structural modifications. The analysis of relaxation times and self-diffusion coefficients indicated that ageing promoted the formation of molecular populations characterized by a shift of the distribution toward higher molecular weights compared to unaged bitumen. Diffusion data showed also an Arrhenius-like temperature dependence. A correlation between all the data was attempted to understand the role of the investigated additives. The eco-friendly biocompatible rejuvenator helped not only to restore the structure of the aged bitumen, but even slowed down the processes of a second aging (aiming at the first aged sample).

Study of ion dynamics of LiI·6H2O in the supercooled liquid state using NMR spectroscopy and ionic conductivity measurements

Ion dynamics in the liquid and supercooled liquid state of LiI·6H2O were studied by nuclear magnetic resonance (NMR) spectroscopy and ionic conductivity measurements. The self-diffusion coefficients of the water molecules and lithium ions were measured by 1H and 7Li pulsed gradient spin echo NMR (PGSE-NMR). The temperature dependences of the DC ionic conductivity and diffusion coefficients of lithium ions and water molecules were well-fitted by the Vogel-Tamman-Fulcher (VTF) law, similar to those of the LiCl·RH2O system. The conductivity and lithium diffusion coefficients of the LiI·6H2O system were more than twice those of LiCl·7H2O in the supercooled liquid state below 200 K, which could be attributed to the larger size of the iodide anions than that of chloride anions. The temperature dependence of the correlation times calculated from NMR T1 relaxation deviated from the VTF law at low temperatures because of the local orientational fluctuation of the water molecules.

TMS self-diffusion coefficients in the binary solvent carbon tetrachloride – acetone-d6. 1H PGSE NMR experiment and random discrete displacements model of self-diffusion

Abstract The tetramethylsilane (TMS) self-diffusion coefficients in the binary solvent carbon tetrachloride (CTC) – acetone-d6 (A-d6) have been obtained by the pulsed gradient spin-echo nuclear magnetic resonance (PGSE NMR) method at 278, 298, and 318 K. The TMS self-diffusion coefficients increase as the A-d6 concentration and temperature become higher. The temperature dependences of the TMS self-diffusion coefficients at various concentrations of the binary solvent have been analysed based on the random discrete displacements model of self-diffusion presented in this paper. Within the framework of the proposed model, it is shown that the Arrhenius type of the temperature dependence of the self-diffusion coefficient (which is observed for TMS in this work) is a special case when the diffusion activation energy ED > kBT. In the opposite case, the temperature dependence of the self-diffusion coefficient tends to the form of the equation obtained for an ideal gas.

Auto-fluorescent PAMAM-based dendritic molecules and their potential application in pharmaceutical sciences.

The epithelial permeation of water-soluble fluorescent PAMAM dendrons based on 7H-benz[de] benzimidazo [2,1-a] isoquinoline-7-one as a fluorescent core across epithelial cell models MDCK I and MDCK II has been quantified. Hydrodynamic radii have been derived from self-diffusion coefficients obtained via pulsed-gradient spin-echo Nuclear Magnetic Resonance (PGSE-NMR). Results indicate that these dendritic molecules are molecularly disperse, non-aggregating, and only slightly larger than their parent homologues. MDCK I permeability studies across epithelial barriers show that these dendritic molecules are biocompatible with the chosen epithelial in-vitro model and can permeate across MDCK cell monolayers. Permeability is demonstrated to be a property of dendritic size and cell barrier restrictiveness indicating that paracellular mechanisms play the predominant role in the transport of these molecules.

Diffusional Motion of Solvated Ions in Super-Concentrated Electrolytes

The evolution of solvation structure and dynamics of aqueous LiTFSI based electrolytes with varying salt concentration and competing divalent (Zn2+, Mg2+ and Ca2+) and ammonium based (Me3EtN+) cations were studied using 7Li, 19F and 1H nuclear magnetic resonance (NMR) spectroscopy and pulsed-field gradient (PFG) NMR methods. The NMR peak intensity analysis (Figure 1(a)), reveals that more than half of Li+, TFSI- and H2O molecules are invisible in liquid NMR spectra, likely due to the loss of mobility (broader NMR line width) associated with formation of bigger solvate clusters at higher salt concentrations. The 7Li, 19F and 1H chemical shift values (Figure 1(b)), were shifted to the higher field (more negative chemical shift values) with salt concentration, indicating the interaction between Li+ cations and TFSI- anions became stronger, while the hydrogen bonding network between H2O molecules became weaker resulting from the localization of water clusters in the solutions. The mobility of the remaining species were analyzed through the PFG-NMR based diffusion measurements (Figure 1(c)). It showed that Li+ cation diffuses relatively faster than TFSI- anion (D H2O>D Li>D TFSI) for these aqueous electrolytes, and differ from non-aqueous electrolyte solutions which traditionally register higher anion diffusion rates (D anion > D Li) [1-4]. The D H2O/D TFSI diffusion ratio showed that the relative mobility of water molecules increases with LiTFSI concentration and by addition of multivalent (Zn2+, Mg2+ and Ca2+) cation salt. The D Li/D TFSI diffusion ratio reaches the maximum value of ~3.4 for the 20 m LiTFSI/H2O solution, and the addition of competing cations tends to minimally affect the lithium diffusion. The different behavior between D H2O/D TFSI and D Li/D TFSI values suggest that the localized water molecules diffuse freely in the higher concentration electrolytes, while the diffusion motions of Li+ cation and TFSI- anion depend strongly on the total composition of the competing ions in the solution. The structural and diffusional properties of high concentration electrolytes will be discussed based on diffusion and chemical shift analysis. References Frömling, T., et al., Enhanced Lithium Transference Numbers in Ionic Liquid Electrolytes. J. Phys. Chem. B, 2008. 112(41): p. 12985-12990.Hayamizu, K., Temperature Dependence of Self-Diffusion Coefficients of Ions and Solvents in Ethylene Carbonate, Propylene Carbonate, and Diethyl Carbonate Single Solutions and Ethylene Carbonate + Diethyl Carbonate Binary Solutions of LiPF6 Studied by NMR. J. Chem. Eng. Data, 2012. 57(7): p. 2012-2017.Hayamizu, K., et al., Pulse-Gradient Spin-Echo 1H, 7Li, and 19F NMR Diffusion and Ionic Conductivity Measurements of 14 Organic Electrolytes Containing LiN(SO2CF3)2. J. Phys. Chem. B, 1999. 103(3): p. 519-524.Wu, T.-Y., et al., Influence of LiTFSI Addition on Conductivity, Diffusion Coefficient, Spin–Lattice Relaxation Times, and Chemical Shift of One-Dimensional NMR Spectroscopy in LiTFSI-Doped Dual-Functionalized Imidazolium-Based Ionic Liquids. J. Chem. Eng. Data, 2015. 60(3): p. 471-483. Figure 1

Toward understanding the anomalous Li diffusion in inorganic solid electrolytes by studying a single-crystal garnet of LLZO-Ta by pulsed-gradient spin-echo nuclear magnetic resonance spectroscopy.

Li diffusion was observed by 7Li nuclear magnetic resonance (NMR) spectroscopy in three single-crystal samples of LLZO-Ta (Li6.5La3Zr1.5Ta0.5O12) grown by the floating zone melting method as well as a crushed sample in this study. Previously, the pulsed-gradient spin-echo 7Li NMR method was applied to Li+ diffusion measurements in inorganic solid electrolyte powder samples. Anomalous Li+ diffusion behaviors were observed such as dependence of the observing time (Δ) and pulsed-field-gradient strength (g), and the diffusive-diffraction patterns in short Δ in the echo-attenuation plots. In the powder samples, it is uncertain that the Li ions diffuse in the bulk within grain, across grains, or both. To date, the origins of the anomalous Li+ diffusion have not yet been clearly understood. From models of atomic-level lithium pathways, the micrometer-space diffusion channels are assumed to be narrow with curvatures. In contrast to the powder samples, a single crystal is supposed to be uniform without grain boundaries and the Li ions in single-crystal samples can diffuse in the bulk with negligible effects from the surface. The single-crystal samples are expected to give us proper answers. We found that the 7Li echo-attenuation plots of the single-crystal samples showed anomalous phenomena in dependence on Δ and g with much reduced manners. We found that the phenomena are inherent characteristics of Li+ diffusion in inorganic solid electrolytes. From the aspects of Li+ carrier numbers, the fast divergent Li+ diffusion constants, observed at short Δ with small g, contribute importantly to the electrochemical high ionic conduction measured by impedance spectroscopy.

The self-diffusion of parabens (methyl-, propylparaben) and tetramethylsilane in the binary solvent carbon tetrachloride – Co-solvent (methanol‑d4, acetone‑d6) at 278, 298 and 318 K

The self-diffusion of parabens (methylparaben, propylparaben) and tetramethylsilane in the binary solvents carbon tetrachloride – co-solvent (methanol‑d4, acetone‑d6) has been investigated by the pulsed gradient spin-echo nuclear magnetic resonance (PGSE NMR) method in the range of temperatures from 278 to 318 K. The self-diffusion coefficients of paraben and tetramethylsilane increase as the concentration of acetone‑d6 increases and have a minimum for paraben and an inflection point for tetramethylsilane when the methanol‑d4 concentration increases. Based on the Stokes-Einstein equation it is shown that the paraben hydrodynamic radius in the binary solvent acetone‑d6 – carbon tetrachloride is practically independent of the acetone‑d6 concentration and has a maximum in the binary solvent methanol‑d4 – carbon tetrachloride. This behavior in both cases is explained by the paraben self-association degree and the heteroassociation degree of paraben – co-solvent.