Gelled Electrolyte Containing Phosphonium Ionic Liquids for Lithium-Ion Batteries.

In this work, new gelled electrolytes were prepared based on a mixture containing phosphonium ionic liquid (IL) composed of trihexyl(tetradecyl)phosphonium cation combined with bis(trifluoromethane)sulfonimide [TFSI] counter anions and lithium salt, confined in a host network made from an epoxy prepolymer and amine hardener. We have demonstrated that the addition of electrolyte plays a key role on the kinetics of polymerization but also on the final properties of epoxy networks, especially thermal, thermo-mechanical, transport, and electrochemical properties. Thus, polymer electrolytes with excellent thermal stability (>300 °C) combined with good thermo-mechanical properties have been prepared. In addition, an ionic conductivity of 0.13 Ms·cm−1 at 100 °C was reached. Its electrochemical stability was 3.95 V vs. Li°/Li⁺ and the assembled cell consisting in Li|LiFePO4 exhibited stable cycle properties even after 30 cycles. These results highlight a promising gelled electrolyte for future lithium ion batteries.

Water sub-diffusion in membranes for fuel cells.

We investigate the dynamics of water confined in soft ionic nano-assemblies, an issue critical for a general understanding of the multi-scale structure-function interplay in advanced materials. We focus in particular on hydrated perfluoro-sulfonic acid compounds employed as electrolytes in fuel cells. These materials form phase-separated morphologies that show outstanding proton-conducting properties, directly related to the state and dynamics of the absorbed water. We have quantified water motion and ion transport by combining Quasi Elastic Neutron Scattering, Pulsed Field Gradient Nuclear Magnetic Resonance, and Molecular Dynamics computer simulation. Effective water and ion diffusion coefficients have been determined together with their variation upon hydration at the relevant atomic, nanoscopic and macroscopic scales, providing a complete picture of transport. We demonstrate that confinement at the nanoscale and direct interaction with the charged interfaces produce anomalous sub-diffusion, due to a heterogeneous space-dependent dynamics within the ionic nanochannels. This is irrespective of the details of the chemistry of the hydrophobic confining matrix, confirming the statistical significance of our conclusions. Our findings turn out to indicate interesting connections and possibilities of cross-fertilization with other domains, including biophysics. They also establish fruitful correspondences with advanced topics in statistical mechanics, resulting in new possibilities for the analysis of Neutron scattering data.

The structural organization of seed oil bodies could explain the contrasted oil extractability observed in two rapeseed genotypes.

MAIN CONCLUSION: The protein, phospholipid and sterol composition of the oil body surface from the seeds of two rapeseed genotypes was compared in order to explain their contrasted oil extractability. In the mature seeds of oleaginous plants, storage lipids accumulate in specialized structures called oil bodies (OBs). These organelles consist of a core of neutral lipids surrounded by a phospholipid monolayer in which structural proteins are embedded. The physical stability of OBs is a consequence of the interactions between proteins and phospholipids. A detailed study of OB characteristics in mature seeds as well as throughout seed development was carried out on two contrasting rapeseed genotypes Amber and Warzanwski. These two accessions were chosen because they differ dramatically in (1) crushing ability, (2) oil extraction yield and, (3) the stability of purified OBs. Warzanwski has higher crushing ability, better oil extraction yield and less stable purified OBs than Amber. OB morphology was investigated in situ using fluorescence microscopy, transmission electron microscopy and pulsed field gradient NMR. During seed development, OB diameter first increased and then decreased 30 days after pollination in both Amber and Warzanwski embryos. In mature seeds, Amber OBs were significantly smaller. The protein, phospholipid and sterol composition of the hemi-membrane was compared between the two accessions. Amber OBs were enriched with H-oleosins and steroleosins, suggesting increased coverage of the OB surface consistent with their higher stability. The nature and composition of phospholipids and sterols in Amber OBs suggest that the hemi-membrane would have a more rigid structure than that of Warzanwski OBs.

In vivo measurement of the size of oil bodies in plant seeds using a simple and robust pulsed field gradient NMR method.

An easy to implement and convenient method to measure the mean size of oil bodies (OBs) in plant seeds is proposed using a pulsed field gradient nuclear magnetic resonance (PFGNMR) approach. PFGNMR is a well-known technique used to study either free or restricted diffusion of molecules. As triacylglycerols (TAG) are confined in OBs, analysis of their diffusion properties is a well-suited experimental approach to determine OB sizes. In fact, at long diffusion time, TAG mean squared displacement is limited by the size of the domain where these molecules are confined. In order to access the OB size distribution, strong intensities of magnetic field gradients are generally required. In this work we demonstrate for the first time that a standard liquid-phase NMR probe equipped with a weak-intensity gradient coil can be used to determine the mean size of OBs. Average sizes were measured for several seeds, and OB diameters obtained by PFGNMR were fully consistent with previously published values obtained by microscopy techniques. Moreover, this approach provided evidence of TAG transfer through the network of interconnected OBs, which is dependent on the ability of adjacent membranes to open diffusion routes between OBs. The main advantage of the NMR method is that it does not require any sample preparation and experiments are performed with whole seeds directly introduced in a standard NMR tube.

NMR 1D-imaging of water infiltration into mesoporous matrices.

It is shown that coupling nuclear magnetic resonance (NMR) 1D-imaging with the measure of NMR relaxation times and self-diffusion coefficients can be a very powerful approach to investigate fluid infiltration into porous media. Such an experimental design was used to study the very slow seeping of pure water into hydrophobic materials. We consider here three model samples of nuclear waste conditioning matrices which consist in a dispersion of NaNO(3) (highly soluble) and/or BaSO(4) (poorly soluble) salt grains embedded in a bitumen matrix. Beyond studying the moisture progression according to the sample depth, we analyze the water NMR relaxation times and self-diffusion coefficients along its 1D-concentration profile to obtain spatially resolved information on the solution properties and on the porous structure at different scales. It is also shown that, when the relaxation or self-diffusion properties are multimodal, the 1D-profile of each water population is recovered. Three main levels of information were disclosed along the depth-profiles. They concern (i) the water uptake kinetics, (ii) the salinity and the molecular dynamics of the infiltrated solutions and (iii) the microstructure of the water-filled porosities: open networks coexisting with closed pores. All these findings were fully validated and enriched by NMR cryoporometry experiments and by performing environmental scanning electronic microscopy observations. Surprisingly, results clearly show that insoluble salts enhance the water progression and thereby increase the capability of the material to uptake water.

Almost ideal 1D water diffusion in imogolite nanotubes evidenced by NMR relaxometry.

The longitudinal proton relaxation rates R(1) of water diffusing inside synthetic aluminium silicate imogolite nanotubes are measured by fast field-cycling NMR for frequencies between 0.02 and 35 MHz at 25, 37 and 50 degrees C. We give analytical expressions of the dominant intermolecular dipolar spin-spin contribution to R(1) and to the transverse relaxation rate R(2). A remarkable variation of R(1) by more than two orders of magnitude is observed and shown to be close to the theoretical law, inversely proportional to the square root of the resonance frequency, which is characteristic of perfect molecular 1D diffusion. The physics of diffusion is discussed.

Microscopic structure of heterogeneous lipid-based formulations revealed by 13C high-resolution solid-state and 1H PFG NMR methods.

Lipid-based formulations such as lip glosses that are very alike on the base of their components may have significant differences in their expected macroscopic properties as cosmetics. To differentiate such formulations, high-resolution (13)C NMR was performed under magic angle spinning to investigate the properties at both molecular and microscopic levels. Temperature studies were carried out and no polymorphism in the solid domains could be evidenced after the thermal treatment performed for obtaining the commercial lip glosses. (13)C NMR spectra also showed that some waxes remain partially solubilized in the oils of formulations. The microscopic structure of the wax-oil liquid domains was worked out on the basis of restricted diffusion properties obtained with proton pulsed-field gradient NMR. Changing a single wax component, in two identical formulations, yields significant morphological differences. In the first one the liquid phase appears as a continuum whereas in the second one, the liquid phase is fractionated into micrometric droplets.

Microphase structure of poly(N-isopropylacrylamide) hydrogels as seen by small- and wide-angle X-ray scattering and pulsed field gradient NMR.

Above the lower critical solution temperature T(c) (ca. 34 degrees C), poly(N-isopropylacrylamide) hydrogels become weakly hydrophobic and undergo microphase separation. Macroscopic deswelling, however, is extraordinarily slow, the out-of equilibrium state of the gel being conserved for many days. In this article the structure of the microphase-separated state above T(c) is probed by small-angle X-ray scattering and by pulsed field gradient NMR of the protons of water, both in the water phase and in the polymer-rich phase. Above T(c) the gel comprises two microphases, separated by smooth interfaces. The cavities occupied by the water phase form a connected network. The diffusion rate of the water molecules in this phase varies from one cavity to another and can be described by a Gaussian distribution. Water molecules belonging to the polymer-rich phase are also mobile, but their self-diffusion coefficient D is greatly diminished. Absence of compartmentalization of the water phase implies that the slow deswelling rate of the gel is not due to trapping of the water phase.

NMR and pulsed field gradient NMR approach of water sorption properties in Nafion at low temperature.

The water uptake and the water self-diffusion coefficient were measured in Nafion membranes at subzero temperatures. NMR spectroscopy was used to precisely quantify the actual concentration of water in membranes as a function of the temperature and their hydration rates at room temperature. We find that below 273 K the water concentration decreases with temperature to reach, at around 220 K, a limit value independent of the initial concentration. This regime is observed if the concentration at room temperature is higher than 10%. Below this concentration no membrane deswelling was observed. The water self-diffusion coefficient, measured by pulsed field gradient NMR in function of the temperature, is determined by the actual concentration C(T) whatever the concentration at room temperature. The concentration variation is attributed to a decrease in the relative humidity RH(T) of the water vapor surrounding the membrane induced by the simultaneous presence of supercooled water inside the membrane and ice outside the membrane.

In situ pulsed-field gradient NMR determination of the size of oil bodies in vegetable seeds. Analysis of the effect of the gradient pulse length.

We report a pulsed-field gradient NMR study of the size of the oil bodies in lettuce seeds. The pulsed-field gradient spin-echo method (PFGSE) was applied to measure the self-diffusion coefficient of triacylglycerol molecules (TAG) inside the oil bodies. The confined nature of TAG diffusion is used to determine the size dispersion of the oil bodies. At long diffusion time, we measure a spin-echo attenuation that is related to the form factor of the confining volumes in the reciprocal q space, where q is proportional to the product of the gradient intensity and the length of the pulse gradient. Specific care was taken in analyzing the influence of the gradient pulse length delta on the shape of the PFGSE decay in order to construct the function corresponding to the short gradient pulse approximation (SGP). The SGP model gives an analytical framework for the PFGSE signal that enables the size distribution of the oil bodies to be determined. The SGP function was unambiguously obtained by varying the gradient pulse length delta in order to linearly extrapolate at delta = 0 the SGP limit. In this work, we also consider the Gaussian phase distribution (GPD) assumption that is often used to analyze confined diffusion experiments. Although the GPD assumption is known to be inaccurate in predicting the fine structure of the PFGSE function in q space, we point out that in the present case it can be used to take into account the finite value of delta. A log-normal distribution of the radius values was assumed in simulating the PFGNMR experiments since this type of distribution is observed in vegetable seeds by transmission electronic microscopy. From a practical and experimental standpoint, the NMR measurements reported here require no specific treatment of the seeds and the size of oil bodies is determined "in situ" on seeds poured into the NMR tube.

Water dynamics in ionomer membranes by field-cycling NMR relaxometry.

The dynamic behavior of water within two types of ionomer membranes, Nafion and sulfonated polyimides, has been investigated by field-cycling nuclear magnetic relaxation. This technique, applied to materials prepared at different hydration levels, allows to probe the proton motion on a time scale of the microsecond. The NMR longitudinal relaxation rate R(1) measured over three decades of Larmor angular frequencies omega is particularly sensitive to the host-water interactions and thus well suited to study fluid dynamics in restricted geometries. In the polyimide membranes, we have observed a strong dispersion of R(1)(omega) following closely a 1/sqrt[omega] law in a low-frequency range (correlation times from 0.1 to 10 micros). This is indicative of a strong interaction of water with "interfacial" hydrophilic groups of the polymeric matrix (wetting situation). On the contrary, in the Nafion, we observed weak variations of R(1)(omega) at low frequency. This is typical of a nonwetting behavior. At early hydration stages, the proton-proton inter-dipolar contribution to R(1)(omega) evolves logarithmically, suggesting a confined bidimensional diffusion of protons in the microsecond time range. Such an evolution is lost at higher swelling where a plateau related to 3D diffusion is observed.

Water dynamics in ionomer membranes by field-cycling NMR relaxometry.

The dynamic behavior of water within two types of ionomer membranes, Nafion and sulfonated polyimide, has been investigated by field-cycling nuclear magnetic relaxation. This technique, applied to materials prepared at different hydration levels, allows the proton motion on a time scale of microseconds to be probed. The NMR longitudinal relaxation rate R(1) measured over three decades of Larmor angular frequencies omega is particularly sensitive to the host-water interactions and thus well-suited to study fluid dynamics in restricted geometries. In the polyimide membranes, we have observed a strong dispersion of R(1)(omega) following closely a 1/square root omega law in a low-frequency range (correlation times from 0.1 to 10 micros). This is indicative of a strong interaction of water with "interfacial" hydrophilic groups of the polymeric matrix (wetting situation). Variations of the relaxation rates with water uptake reveal a two-step hydration process: solvation and formation of disconnected aqueous clusters near polar groups, followed by the formation of a continuous hydrogen bond network. On the contrary, in the Nafion we observed weak variations of R(1)(omega) at low frequencies. This is typical of a nonwetting behavior. At early hydration stages, R(1)(omega) evolves logarithmically, suggesting a confined bidimensional diffusion of protons in the microsecond time range. Such an evolution is lost at higher swelling where a plateau related to three-dimensional diffusion is observed.

Investigation of gamma-irradiated vegetable seeds with high-resolution solid-state 13C NMR.

13C solid-state NMR was used to investigate the effects of gamma radiation on vegetable seeds, Pisum sativum and Latuca sativa, at absorbed doses that inhibit their germination. By combining single-pulse excitation and cross-polarization experiments under magic angle spinning, both liquid and solid domains of seeds can be characterized. We showed that the liquid domains, mostly made of triacylglycerols (TAG), of vegetable seeds are not sensitive to radiation. The main structural changes have been observed in the embryonic axes of seeds when the seeds are water-imbibed before irradiation. These results rule out a starting hypothesis concerning the potential role of TAG contained in oil bodies as a potential source of aldehydes that could further react with DNA moiety.