Quadrupolar Na NMR relaxation as a probe of subpicosecond collective dynamics in aqueous electrolyte solutions.

Nuclear magnetic resonance relaxometry represents a powerful tool for extracting dynamic information. Yet, obtaining links to molecular motion is challenging for many ions that relax through the quadrupolar mechanism, which is mediated by electric field gradient fluctuations and lacks a detailed microscopic description. For sodium ions in aqueous electrolytes, we combine ab initio calculations to account for electron cloud effects with classical molecular dynamics to sample long-time fluctuations, and obtain relaxation rates in good agreement with experiments over broad concentration and temperature ranges.

Comparison of experimental times in T-D and D-T correlation experiments in single-sided NMR.

Diffusion-relaxation correlation experiments in nuclear magnetic resonance are a powerful technique for the characterization of fluid dynamics in confined geometries or soft matter, in which relaxation may be either spin-spin (T) or spin-lattice (T). The general approach is to acquire a set of bidimensional data in which diffusion is codified by the evolution of the magnetization with either Hahn or stimulated echoes (STE) in the presence of a constant magnetic field gradient. While T is codified by a Carr-Purcell-Meiboom-Gil (CPMG) sequence, T is either encoded by saturation or inversion-recovery methods.

Sensitive magnetometry reveals inhomogeneities in charge storage and weak transient internal currents in Li-ion cells.

The ever-increasing demand for high-capacity rechargeable batteries highlights the need for sensitive and accurate diagnostic technology for determining the state of a cell, for identifying and localizing defects, and for sensing capacity loss mechanisms. Here, we leverage atomic magnetometry to map the weak induced magnetic fields around Li-ion battery cells in a magnetically shielded environment. The ability to rapidly measure cells nondestructively allows testing even commercial cells in their actual operating conditions, as a function of state of charge.

Diagnosing current distributions in batteries with magnetic resonance imaging.

Batteries and their defects are notoriously difficult to analyze non-destructively, and consequently, many defects and failures remain little noticed and characterized until they cause grave damage. The measurement of the current density distributions inside a battery could reveal information about deviations from ideal cell behavior, and could thus provide early signs of deterioration or failures. Here, we describe methodology for fast nondestructive assessment and visualization of the effects of current distributions inside Li-ion pouch cells.

Single-shot velocity mapping by rewinding of velocity encoding with Echo-Planar Imaging.

The ability of single-shot NMR imaging methods to follow the time evolution of a velocity distribution within an object is strongly limited by the phase errors accumulated as velocity maps are acquired. In the particular case of Carr-Purcell based sequences combined with Echo Planar Imaging acquisition, phase accumulates through subsequent images, hampering the possibility to acquire several velocity maps, which would be useful to determine transient behavior. In this work, we propose the use of a rewinding velocity encoding module applied after the acquisition of each image during the CPMG echo train.

Multinuclear absolute magnetic resonance thermometry.

Non-invasive measurement of absolute temperature is important for proper characterization of various pathologies and for evaluation of thermal dose during interventional procedures. The proton (hydrogen nucleus) magnetic resonance (MR) frequency shift method can be used to map relative temperature changes. However, spatiotemporal variations in the main magnetic field and the lack of local internal frequency reference challenge the determination of absolute temperature.

Unusual Proton Transfer Kinetics in Water at the Temperature of Maximum Density.

Water exhibits numerous anomalous properties, many of which remain poorly understood. One of its intriguing behaviors is that it exhibits a temperature of maximum density (TMD) at 4 °C. We provide here new experimental evidence for hitherto unknown abrupt changes in proton transfer kinetics at the TMD.

Monitoring Molecular Transport across Colloidal Membranes.

The controlled shaping and surface functionalization of colloidal particles has provided opportunities for the development of new materials and responsive particles. The possibility of creating hollow particles with semipermeable walls allows modulating molecular transport properties on colloidal length scales. While shapes and sizes can typically be observed by optical means, the underlying chemical and physical properties are often invisible.

Probing numerical Laplace inversion methods for two and three-site molecular exchange between interconnected pore structures.

Two-dimension (2D) Nuclear Magnetic Resonance relaxometry experiments are a powerful tool extensively used to probe the interaction among different pore structures, mostly in inorganic systems. The analysis of the collected experimental data generally consists of a 2D numerical inversion of time-domain data where T-T maps are generated. Through the years, different algorithms for the numerical inversion have been proposed.

Flow-Pattern Characterization of Biphasic Electrochemical Cells by Magnetic Resonance Imaging under Forced Hydrodynamic Conditions.

The fluid dynamics of a liquid|liquid system inside a four-electrode electrochemical cell were studied by velocimetry magnetic resonance imaging (MRI) and flow propagator measurements. To characterize this system fully, three different cell configurations operating at two rotational frequencies were analyzed. Quantitative information about the stability of the liquid|liquid interface and the dynamics of the organic phase were determined.

Enhanced Surface Interaction of Water Confined in Hierarchical Porous Polymers Induced by Hydrogen Bonding.

Hierarchical porous polymer systems are increasingly applied to catalysis, bioengineering, or separation technology because of the versatility provided by the connection of mesopores with percolating macroporous structures. Nuclear magnetic resonance (NMR) is a suitable technique for the study of such systems as it can detect signals stemming from the confined liquid and translate this information into pore size, molecular mobility, and liquid-surface interactions. We focus on the properties of water confined in macroporous polymers of ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate [poly(EGDMA-co-HEMA)] with different amounts of cross-linkers, in which a substantial variation of hydroxyl groups is achieved.

Spatially Resolved Monitoring of Drying of Hierarchical Porous Organic Networks.

Evaporation kinetics of water confined in hierarchal polymeric porous media is studied by low field nuclear magnetic resonance (NMR). Systems synthesized with various degrees of cross-linker density render networks with similar pore sizes but different response when soaked with water. Polymeric networks with low percentage of cross-linker can undergo swelling, which affects the porosity as well as the drying kinetics.

Desktop MRI as a promising tool for mapping intra-aneurismal flow.

In this work we evaluate the performance of a 40-mm diameter bore 0.2T desktop Halbach tomograph to obtain 2D and 3D velocity maps for studying intra-aneurismal flow in the presence or absence of nitinol meshed implants with the aim of optimizing the flow diverter efficacy. Phantoms with known spatial velocity distribution were used to determine the performance of the MRI system.

Evaporation kinetics in swollen porous polymeric networks.

NMR is a fast, nondestructive, and noninvasive technique that can provide information about the pore structure of macroporous polymer beads and the dynamics of liquids confined in them. In this work, we describe the study of the pore structure of the macroporous polymer of ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate [poly(EGDMA-co-HEMA)] in the dry but also in the swollen state by measuring relaxation times of liquids contained in the polymer network. The results show that the pore architecture differs from the dry to the soaked state.