NMR Microimaging Technique Research Articles

Direct Observation of Electrophoretic Flow of Solvent Molecules with Lithium Ions By NMR Imaging

Lithium ion transport in the organic liquid electrolyte is a key process in conventional lithium ion batteries, where the lithium ion shuttles between the positive and negative electrodes while the charging and discharging process. The translational motion of the lithium ion in the liquid electrolyte is accompanied by the coordinating organic solvent molecules such as EC, DMC etc., which must be detached from the lithium ion at the electrodes by the desolvation process. On the other hand, the counter anions such as PF6 - is thought to move opposite direction, although the local concentration is the same to that of lithium cation in order to keep the electroneutrality condition. Although this picture is based on many evidences by electrochemical measurements, the direct observation of the correlated motion of the lithium ions and solvated molecules has not been reported. In this paper, we first demonstrate the direct observation of the translational motion of solvent molecules (EC,DEC) with the lithium ions by using NMR micro-imaging technique. NMR microimaging is observed by Avance 400 spectrometer equipped with mini-Imaging probe by Bruker Co. The 1H and 19F NMR imaging are observed in this measurement. Model cell is constructed in NMR spectrometer, which is composed by LiMn2O4 cathode, lithium metal anode and liquid electrolyte of EC/DMC+LiPF6. The cell is connected to an electrochemical charge-discharge set-up to operate the cell. Small desolution of Mn2+ from the cathode acts as a contrast agent to enhance the flow image of the cell. Some vertical images of the cell in a charge-discharge process are shown in Fig. 1, where the LiMn2O3 positive electrode is located at the bottom and the lithium metal anode is on the top. Constant current mode of 25 mA is used. While the charging current is set upward from LiMn2O3 cathode to the lithium anode, namely the Li+ cations move upward, then the proton NMR imaging observing the motion of the EC and DMC molecules is confirmed to upward, which is the same direction as that of the Li+ ions. Moreover, the flowing current of the solvent moves toward left and right directions near the lithium anode, where the EC and DMC should release the Li+ to the anode and move aside. This continuous flow generates an electroconvection which can be seen in Fig. 1 as a vortex curling from center to the side wall. On the other hand, when the current is reversed to discharge, the flow of the solvent changes its direction from the top (anode) to the bottom (cathode), which generate the reverse vortex as shown in Fig. 1. Figure 1

Magnetic resonance imaging (MRI) study of the water content and transport in rat lenses

NMR micro-imaging technique has been used for the measurement of the water content distribution in lenses of senescence-accelerated OXYS rats and age-matched Wistar rats, as well as for the study of water and phosphate transport in rat lenses. The water content in the lens cortex is significantly higher than in the nucleus; the spatial gradient of the water content becomes steeper with age. No difference in the water content distribution has been found between Wistar and OXYS rat lenses of matching ages, although cataract onset in the OXYS rat lens occurs much earlier due to the enhanced generation of reactive oxygen species associated with oxidative stress. This finding implies that cataract development does not lead to significant changes in water content distribution inside the lens. The water transport in rat lenses slows down with age, and in OXYS lenses it is somewhat faster than in lenses of Wistar rats, probably due to the compensatory response to oxidative stress. The application of 31P MRI for the monitoring of phosphate penetration into a lens has been performed for the first time. It is found that phosphate transport in a lens is significantly slower than that of water.

Microscopic states of water and methanol in Nafion membrane observed by NMR micro imaging

Direct methanol fuel cell (DMFC) is a promising energy source for potable electric devices. However the local structure and the transport mechanism of the water and the methanol in the solid electrolyte membrane have not been well understood. In this paper is reported the recent results of the proton NMR spectra and diffusion measurements of water and methanol in Nafion 117. Also, the NMR micro-imaging technique has been applied for the diffusion and exchange of water molecules in the membrane.The chemical shift decreased monotonically as the water content increased and the slope was found to change at water uptake ratio N~6, probably corresponding to the different environment of protons in the membrane. Water and methanol contents in the Nafion membrane immersed in their solution were evaluated from the spectra.Diffusion of the water molecule into and out of the Nafion membrane was visually observed by using NMR micro-imaging technique. Exchange process of the water (H2O) and heavy water (D2O) in a small Nafion ball (3 mm diameter) was observed and density profile of proton was analyzed to give the mutual diffusion coefficient of water and D2O in the Nafion ball.

Cleaner techniques for the preservation of raw goat skins

As the popular salt curing system is considered detrimental to the environment, a search for safer alternative systems has been a top priority research in the area of leather science. The ill-effects of sodium chloride on the environment and eco-system need no emphasis. Hence there is an urgent need for the development and adoption of a viable cleaner curing system. In the present study, a short-term preservation technique using silica gel has been studied and standardized. The possibility of using silica gel in place of salt as a curing agent alone and in combination with a suitable biocide was studied at an ambient temperature of 31°C. The preservation efficacy of the methods was assessed by various parameters such as moisture content, total extractable nitrogen, and bacterial count. The layer wise moisture content was determined using a NMR micro-imaging technique. The effect of the new curing methods on the fibre structure of treated skins was assessed using scanning electron microscopic (SEM) studies. The pollution load generated in the processing of the skins treated using the new techniques is compared with that for salt cured stock. The results show that the cleaner preservation techniques developed were as efficient as salt curing for the preservation of skins. The new curing methods did not pose any problem either in soaking or in the leather manufacturing processes. The methods developed are found to be effective and viable options for combatting the pollution problems of chloride and total dissolved solids (TDS).

Application of the 1H NMR Microimaging Technique to in situStudies of Evaporation of Liquids from Objects Modeling Porous Solids

Application of the 1H NMR Microimaging Technique to in situStudies of Evaporation of Liquids from Objects Modeling Porous Solids

An 1H NMR Microimaging Visualization of Hexachloroplatinate Dianion Redistribution within a Porous γ-Al2O3 Pellet in the Course of Supported Catalyst Preparation

The application of the 1H NMR microimaging technique to the indirect mapping of the spatial distribution of hexachloroplatinate dianion within porous alumina pellets is reported. It is demonstrated that the nuclear spin−lattice relaxation times of liquids filling the pores of the pellet increase in the presence of the adsorbed hexachloroplatinate dianion. The microimaging results for the supported catalysts with two types of platinum distribution (egg-shell and egg-white) are shown to be consistent with the results obtained by the staining method and electron probe microanalysis. Finally, the microimaging technique is employed for a nondestructive visualization of the dynamics of the active component redistribution in the course of the supported catalyst preparation by competitive adsorption.

An 1H NMR Microimaging Study of Water Vapor Sorption by Individual Porous Pellets

The 1 H NMR microimaging technique is applied to study water vapor sorption by the individual cylindrical silica gel and alumina pellets impregnated with hygroscopic salts. The two-dimensional images or the onedimensional profiles of the sorbed water distribution are detected sequentially to monitor the transport of water within the pellets in real time in the course of the sorption process. The results identify the propagation of the sorbed water front through the dry regions of the pellets as the rate-limiting stage of the sorption process. This propagation can be facilitated by employing the pellets with the eggshell distribution of the salt, but in such cases the salt redistributes readily in the course of the sorption process, as revealed by the relaxation weighted 1 H NMR microimaging experiments in which paramagnetic salts are used. The diffusion equation with water content dependent diffusivity is employed to model the one-dimensional radial profiles of water distribution within the pellet with appropriate correction for the relaxation weighting effects.

A quantitative NMR imaging study of mass transport in porous solids during drying

The temporal transformations of the radial distribution of a liquid in a presoaked porous cylindrical catalyst support pellet detected by 1 H NMR microimaging technique in the course of the pellet drying are analyzed quantitatively in terms of the diffusion equation. The approach is shown to be adequate for evaluating the diffusivity and its dependence on the degree of pellet saturation with a liquid, provided that the NMR microimaging data are properly corrected for the relaxation weighting effects. It is demonstrated that for liquids characterized by a low surface tension, such as acetone, benzene and cyclohexane, transformations of the concentration profiles can be adequately modeled assuming a liquid content-independent diffusivity. In contrast, the diffusivity of water in titania and alumina pellets substantially decreases with the decrease of water content. For alumina pellets with a pronounced “bimodality” in the pore size distribution the water concentration dependence of diffusivity is shown to be non-monotonic. It is argued that for liquids with high surface tension, the shape of the concentration profiles and the behavior of diffusivity as a function of liquid content are both related to the shape of the cummulative pore size distribution of the porous solid under study due to the existence of efficient capillary flows induced by capillary suction.

Detection of Anisotropic Pulsating Flow and Its Velocity-Fluctuation Rate in Fertilized Bird Eggs by NMR Microimaging

Coherent and incoherent flows in fertilized quail and bantam eggs have been studied with the aid of NMR microimaging techniques in the course of incubation until the end of the sixth day. The methods employed were multiplane tagging NMR imaging and a NMR gradient-echo imaging pulse sequence supplemented by bipolar gradient pulses in the coherence-evolution interval. The latter technique is suited for recording of velocity maps as well as for localizing of regions with enhanced echo attenuation by incoherent motions. Slight coherent displacements in the middle of the upper part of the egg white were found after the fourth day of incubation with the aid of both pulse schemes. The maximum velocity was estimated to be 1 mm/s. More pronounced effects revealed themselves in the examination of incoherent motions. After the same time of incubation and in a somewhat more restricted area of the upper part of the egg white, distinct motions could be localized consistently with either technique. It is shown that these motions are directed to and from the yolk. Furthermore, the analysis of the time fluctuations of the local signals with the aid of a Fourier transformation showed that the flow is largely of a pulsating nature. The pulsation frequency was found to be 0.4 Hz.

Visualization of anisotropic pulsations in extraembryonic compartments of incubated quail eggs by NMR microimaging

Multi-plane tagging time-of-flight and bipolar gradient phase-encoding and amplitude-weighting NMR microimaging techniques have been employed to study transport in extraembryonic compartments of fertilized quail eggs during the first seven days of incubation. After the fourth day coherent and incoherent motions became visible in certain regions, in particular in the upper part of the albumen. Coherent motions as visualized by deformations of multiplane tagging grids were specified by local velocities less than 1 mm/s at most. On the other hand, incoherent motions led to much more pronounced phenomena. The multiplane tagging grid completely faded in a region comprising the upper third of the albumen after 4.5 incubation days. Images weighted by signal attenuation owing to incoherent displacements indicate motions in the same region. The fact that a reproducible localization of the motions is only possible when signals from different transients are averaged indicates that the incoherence at least partly is temporal in nature. The signal intensity of a volume selected in the incoherent-motion region consequently fluctuates with time. The Fourier analysis of these fluctuations revealed a distinct pulsation with a frequency of 0.4 Hz.