Nuclear Magnetic Resonance Relaxation Times Research Articles

Feasibility of Surface Nuclear Magnetic Resonance With Absurdly Long Excitation Pulses

AbstractThe common understanding in surface nuclear magnetic resonance (NMR) is that the excitation pulse should be kept much shorter than the NMR relaxation times for an effective excitation. We present analytic, numerical, and experimental evidence demonstrating that this need not be so, and surface NMR signals can be retrieved even for absurdly long excitation pulses. We solve the Bloch equations in the limit of infinitely long excitation and use this result to demonstrate that a measurable magnetization can be obtained with long excitation pulses. We perform numerical simulations of the Bloch equations incorporating effects of relaxation‐during‐pulse, and our results suggest that long excitation pulses can be used to increase the depth of investigation, but that the spatial resolution of long pulse excitation is low. Data collected in Kompedal, Denmark using up to 3 s long excitation pulses provide experimental proof for the feasibility of long pulse surface NMR.

Ultrafast T1-T1ρ NMR for Correlating Different Motional Regimes of Molecules.

Nuclear magnetic resonance (NMR) relaxation times provide detailed information about molecular motions and local chemical environments. Longitudinal T1 relaxation time is most often sensitive to relatively fast, nano- to picosecond ranges of molecular motion. Rotating frame T1ρ relaxation time reflects a much slower, micro- to millisecond range of motion, and the motional regime can be tuned by changing spin-lock field strength. Conventional methods for measuring T1 and T1ρ relaxation times are time-consuming, since experiments must be repeated many times with incremented magnetization recovery or decay delay. In this work, we introduce two novel and efficient NMR methods to correlate the T1 and T1ρ relaxation times. The first method, IR-SPICY, combines the conventional T1 inversion recovery (IR) with the single-scan T1ρ detection-based spin-lock cycle (SPICY). The second method, ultrafast (UF) IR-SPICY, allows measurement of whole two-dimensional T1-T1ρ correlation data in a single scan, in a couple of seconds, based on spatial encoding of the T1 dimension. We demonstrate the performance of the methods by studying relaxation of water in porous silica and hydrogel samples, latter acting as a model of the articular cartilage extracellular matrix. The methods allow correlating different molecular motional regimes, potentially providing unprecedented information about various chemical and biochemical systems, such as structures and fluid dynamics in porous materials, macromolecular changes in tissues, and protein dynamics. One to three orders of magnitude shortened experiment time enable the studies of changing or degrading samples. Furthermore, the single-scan approach may significantly facilitate the use of modern nuclear-spin hyperpolarization techniques to enhance the sensitivity of T1-T1ρ measurements by several orders of magnitude.

Supramolecular Arrangement and Conformational and Dynamic Properties of Chiral Smectic Liquid Crystals Obtained through Nuclear Magnetic Resonance: A Brief Review

Ferroelectric and antiferroelectric smectic liquid crystalline (LC) phases are still at the center of investigations and interests for both their fundamental properties and variety of technological applications. This review aims to report the main contributions based on different nuclear magnetic resonance (NMR) techniques to the study of chiral liquid crystalline calamitic mesogens forming smectic phases, such as the SmA, the SmC* (ferroelectric), and the SmC*A (antiferroelectric) phases. 2H NMR and 13C NMR techniques and their combination were of help in clarifying the local orientational properties (i.e., the molecular and fragments’ main orientational order parameters) at the transition between the SmA and the SmC* phases, and in the particular case of de Vries liquid crystals, NMR studies gave important clues regarding the actual models describing the molecular arrangement in these two phases formed by de Vries LCs. Moreover, this review describes how the combination of 2H NMR relaxation times’ analysis, 1H NMR relaxometry, and 1H NMR diffusometry was successfully applied to the study of chiral smectogens forming the SmC* and SmC*A phases, with the determination of relevant parameters describing both rotational molecular and internal motions, collective dynamics, and translational self-diffusion motions. Several cases will be reported concerning NMR investigations of chiral ferroelectric and antiferroelectric phases, underlining the great potential of combined NMR approaches to the study of supramolecular, conformational, and dynamic properties of liquid crystals.

Multi-shelled hollow porous carbon nanospheres-based evaporator for highly efficient solar-driven desalination

Carbon-based materials stand out as photothermal materials for interfacial solar evaporation due to their high solar absorptance, chemical stability, adjustable structure, ease of preparation, and low cost compared to other candidate materials. Development of multifunctional carbon-based materials that can endow the fabricated evaporators with reduced energy loss and evaporation enthalpy is highly demanded to achieve extraordinary evaporation rates. Herein, high-solar-absorptivity multi-shelled hollow porous carbon nanospheres are fabricated and incorporated with an insulating hydrogel bottom layer into an integrated solar evaporator. It achieves a fast photothermal response and a remarkably high solar evaporation rate of 2.4 kg m−2 h−1 under one sun. Multiphysics simulation indicates that the porous multi-shelled hollow structure enables sufficient and effective interactions between water and the hydrophilic carbon surfaces, thus producing more intermediate water (IW) and lowering the evaporation enthalpy. The solar-driven water evaporation in the evaporator is probed by in-situ low-field nuclear magnetic resonance relaxation time measurements, based on which conversion of free water (FW) into IW during solar evaporation is proposed. The molecular dynamics simulations reveal that the evolution of FW clusters into IW is facilitated on the carbon surface, thus replenishing the evaporated IW and maintaining continuous high evaporation rates. The demonstrated solar evaporator exemplifies the effectiveness of structural and thermal management in enhancing solar-driven desalination.

Understanding Ion Dynamics in Closoborate-Type Lithium-Ion Conductors on Different Time-Scales.

The lithium-ion transport mechanism in 0.7Li(CB9H10)-0.3Li(CB11H12) complex hydride solid electrolyte was studied over a wide time-scale (ns-ms) by choosing appropriate techniques for assessing ionic motion on the desired time-scale using nuclear magnetic resonance (NMR) relaxation, AC impedance, and pulsed field gradient-NMR (PFG-NMR) measurements. The 7Li NMR line width decreased with increasing temperature, and the spin-lattice relaxation time T1 for the cation and anions showed a minimum near 303 K, indicating that the lithium ions and the anions were highly mobile. The activation energy estimated from the analysis of the NMR relaxation time matched well with the values estimated from the AC impedance and PFG-NMR. This confirms that the lithium-ion motion in 0.7Li(CB9H10)-0.3Li(CB11H12) is the same over a wide time-scale, suggesting steady Li-ion motion over a wide transport range. This understanding offers insights into strategies for designing complex hydride lithium superionic conductors.

Physical and Chemical Methods to Assess Performance of TPO-Modified Asphalt Binder

The demand for effective asphalt additives is growing as road infrastructure ages and more sustainable pavement solutions are needed. Tire pyrolysis oil (TPO) is an example material that has been gaining attention as a potential asphalt additive. While physical performance grade (PG) temperatures are the predominant performance requirements for asphalt binders, chemical properties are also significant in the evaluation of asphalt performance. There is a need to chemically characterize the aging of asphalt binders modified with TPO and link chemical changes in binder components to binder performance. This study compares 2%, 4%, and 8% TPO and asphalt binder blends via dynamic shear rheometry (DSR), Fourier-transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) relaxometry. The variability in the modified blends was seen by both physical and chemical testing during four different blending times (1, 60, 120, and 240 min). After blending, high and intermediate PGs were determined by physical testing. The 8% TPO blend reduced the high PG of the binder from 64 °C to 58 °C. This effect was confirmed by chemical testing through changes in carbonyl indices and NMR relaxation times. With more oil present in the binder matrix, the binder’s resistance to rutting was reduced. While the high PG was hindered, the intermediate PG remained unchanged for all TPO blends. This physical similarity was mirrored in chemical testing. The chemical and physical variability along with the hindrance of the high PG temperature indicate that more treatment may be needed before TPO can be effectively applied to asphalt binders. This study suggests a correlation between physical performance and key chemical indicators.

Magnetic resonance imaging: an innovative approach to observe rare metal extraction using ionic liquid.

In the present work, a novel approach has been made to evaluate the extraction mechanism of neodymium (Nd) using trihexyl-tetradecyl-phosphonium benzoate (TTPB) ionic liquid through nuclear magnetic resonance (NMR) techniques. A detailed study on the interactions between the extractant (Nd) and the ionic liquid (IL) is presented. The 1H NMR spectral analysis confirmed that Nd extraction took place through the benzoate anion. Furthermore, the NMR relaxation time of the anion is greatly affected affirming that Nd extraction indeed took place through the benzoate anion. This change in the relaxation time caused by the Nd ion on the protons in the anion and cation in TTPB has been used to visualize the extraction mechanism using 1H MRI. A strong change in the image intensity with respect to the time observed in the IL phase validates the extraction of Nd from the aqueous phase into the IL phase. Also, combining the 1H NMR, diffusion coefficient, Karl-Fischer and ultraviolet-visible absorption spectroscopic (UV-Vis) results, we have elucidated the co-ordination structure around Nd during the extraction process.

Experimental study on the influence of ultrasonic excitation duration on the pore and fracture structure and permeability of coal body

The study aims to explore the effect of ultrasonic duration on the pore structure and seepage characteristics of coal. Herein, we adopted a self-developed ultrasonic excitation experiment system using low-field nuclear magnetic resonance (NMR) technology and NM-4B non-metallic ultrasonic wave velocity detector. The study investigated NMR relaxation time T2 patterns and the number of pores of each size, internal structural damage, and seepage characteristics of the coal body before and after ultrasonic fracturing. Based on the Warren-Root model, the permeability model of coal under ultrasonic fracturing was established, revealing the changing law of ultrasonic fracturing at different times on the change of pore scale, connectivity, and nuclear magnetic permeability of the coal body. The mechanism of ultrasonic fractured coal body evolution at different times was clarified. The results showed that the ultrasonic fracturing at different times improved the number and volume of all size pores in the coal body, expanded primary fractures, and developed newborn fractures. The rate of change in pore size, porosity, wave velocity, and coal permeability had a linear relationship with the fracturing time. The growth rate of seepage pore volume proportion was positively correlated to the decreased rate of adsorption pore volume proportion. The fracturing duration leads to the interconnection of micropores within the coal body, forming medium and large pore fractures. This transformation between pores and fractures enhances the pore structure and seepage characteristics of the coal body. The coal rock permeability model can be used to calculate the permeability of a coal body, which follows the same change law as nuclear magnetic permeability. When evaluating the index using absolute and relative errors, the range of relative error is 0.97%–7.91%. The error variation range is small, indicating that the established model can effectively reflect the change law of porosity and permeability of the coal body responding to ultrasonic fracturing. The ultrasonic fracturing rendered the ultrasonic cavitation takes micropores as fracturing units, developed pores of all sizes, connected closed pores, increased free fluid space proportion, and improved the coal permeability.

Green synthesis of biocompatible Gd3+-doped ultrasmall carbon-based nanohybrids from coffee wastes

A cheap method allowing fabrication of biocompatible, ultra-small (2–10 nm) and fluorescent (λem = 425–500 nm) nanohybrids (NHs) from coffee wastes is reported. The gadolinium-doped nanohybrids (GDNHs) or gadolinium-free carbon dots (GFCDs) can be synthesized in a domestic microwave oven according to green synthesis principles. Hydrodynamic sizes, chemical composition, impact on proton magnetic resonance relaxation time and optical properties of the GDNHs and GFCDs were studied in details and compared. In particular, doping of the NHs with Gd3+ ions, up to 1.87 % w/w of gadolinium per particles’ weight, will allow their application for magnetic resonance imaging (MRI). Furthermore, cell culture tests on human adenocarcinomic alveolar basal epithelial cells line (A549) have shown high biocompatibility of the GDNHs and in a wide concentration range 100–1000 µg/ml.

Molecular insights into nuclear-magnetic-resonance properties of NaCl solution confined within calcite nanopores

Nuclear magnetic resonance (NMR) relaxation time is an important petrophysical property probing fluid dynamics within pores and providing valuable information to understand solid–fluid interactions and ion-related effects. In this study, we investigate NMR and diffusion properties of confined sodium chloride (NaCl) solutions within calcite nanopores via molecular dynamics (MD) simulations. Density profiles, self-diffusion coefficients, and NMR relaxation times were analyzed as a function of pore size, pore geometry, and NaCl concentration. MD results indicate that the presence of NaCl hinders water movement, resulting in reduced self-diffusion coefficients and relaxation times of water. Nevertheless, the influence of NaCl on water mobility is less than the effects caused by confinement and geometry. Strength of oscillations in water and ion density profiles increases when the slit pore size is reduced to 1 nm, suggesting that water-calcite interactions near pore surfaces are stronger in smaller pore sizes. Analysis of dipole–dipole correlation functions and probability distribution of correlation times shows that ions in aqueous solution have an impact on both intra- and intermolecular interactions. A comprehensive comparison of NMR relaxation times of water in both slit and spherical nanopores reveals that spherical models provide a more accurate representation of the confinement effect induced by pore networks within tight rocks. These findings provide a novel quantitative understanding of the impact of confinement, pore geometry, and ion concentration on the translational and rotational dynamics of confined fluids in calcite nanopores.

Elucidation of Liquid Structures and Transport Properties of Highly Concentrated LiN(SO2F)2/Ethylene Carbonate Electrolytes

The Li+ conduction mechanism in highly concentrated ethylene carbonate (EC) solution of lithium bis(fluorosulfonyl)amide (LiFSA) was studied based on the measurements of thermal properties, density, viscosity, ionic conductivity, self-diffusion coefficients, Raman spectra, and proton nuclear magnetic resonance relaxation time. The compositions of EC and LiFSA were varied from dilute to concentrated states ([EC]/[LiFSA] = 9.2–0.80). For compositions of [EC]/[LiFSA] ≤ 1.5, the free solvents decrease, and contact ion pairs and aggregates become dominant, causing a significant change in the transport properties. Faster diffusion of Li+ compared with solvent (Li+ hopping conduction) was observed when the molar composition of [EC]/[LiFSA] ≤ 1.0 as in the case of sulfolane.

Nanostructure of hydrogenated amorphous silicon (a-Si:H) films studied by nuclear magnetic resonance

The aim of this work is to investigate the nanostructures of nanoporous materials by studying the anisotropy of the nuclear spin–spin and spin–lattice relaxations of the guest molecules trapped in the pores. The nuclear magnetic resonance (NMR) data are analyzed in the framework of the theory of the nuclear relaxation dominated by the dipole–dipole interactions in gas or liquid species contained in nanopores. A distinctive feature of this theory is the establishment of a relationship between the degree of orientation ordering of nanopores in the host matrix and their characteristic volume and the anisotropy of the NMR relaxation times.In this work the complex experimental and theoretical approach was applied to study the nanostructure of hydrogenated amorphous silicon (a-Si:H) films. A feature of this study is the simultaneous investigation of the three (T1, T1ρ, and T2) NMR relaxation times, for the same sample. This allows us to determine not only the degree of orientation ordering of nanopores but also to estimate their size (∼1 nm) and correlation times of the nanopore fluctuations. The obtained results demonstrate that the developed approach is effective in studying details of nanostructure of different nanoporous materials.

Estimating permeability in a limestone geothermal reservoir from NMR laboratory experiments

A wireline NMR (Nuclear Magnetic Resonance) logging tool has recently been deployed in the Dogger geothermal aquifer of the Paris Basin to provide a continuous permeability estimation throughout the reservoir. The complex pore structure of heterogeneous carbonate systems means that careful consideration must be given to standard permeability prediction. A laboratory study was performed on cores from a geothermal well at Bobigny, north of Paris. Petrographic and petrophysical analyses of thin sections, water permeability and laboratory NMR relaxation time T2 were conducted on 72 samples. A classification was established using four main facies and the impact of microporosity and micritization on flow properties was investigated. The range of permeability is wide [0.05–1000 mD] and the evaluation addresses different relationships between permeability and a combination of porosity and T2 distributions. Since the latter distributions can provide an estimation of the pore size distributions and in particular the fraction of microporosity within the total porosity, several possibilities arise for better constraining the permeability relationship. For one facies, permeability is nearly independent of porosity over a porosity range of [0.12–0.22], illustrating the well-known difficulty of predicting permeability in carbonate lithologies. The best permeability prediction is obtained when considering only macroporosity instead of total porosity in a classical power law.

Adsorbate/adsorbent interactions in microporous zeolites: mechanistic insights from NMR relaxation and DFT calculations

Nuclear magnetic resonance (NMR) relaxation is an effective and non-invasive technique for probing guest-host interactions in porous materials. In particular, the ratio of longitudinal-to-transverse nuclear spin relaxation time constants T1/T2 has been demonstrated as a robust indicator of adsorbate/adsorbent interactions in mesoporous media. However, the use of NMR relaxation times in microporous materials to probe interactions and dynamics remains relatively unexplored. Herein, we investigate and describe the effect of the aluminium content in microporous HZSM-5 zeolites on the NMR relaxation times of a range of common liquid probe molecules. In particular, we discuss the NMR relaxation time behavior of liquids with hydrophilic (water, methanol) and hydrophobic (toluene, methyl cyclohexane) properties adsorbed over HZSM-5 samples with varying silica-to-alumina ratios (SAR = SiO2/Al2O3). Our results demonstrate that highly polar molecules show high sensitivity to aluminium content (i.e., surface acidity), with T1/T2 ratios increasing significantly for higher acidity zeolites. Conversely, for molecules with low polarity, the T1/T2 ratio as a function of SAR remains approximately constant, and in the zeolites with low SAR is much lower compared to that of water and methanol. Density functional theory (DFT) calculations are employed to contrast the surface interaction mechanisms of water and toluene within model zeolite structures of varying SAR, and provide molecular level insights into the observed trends in NMR relaxation behavior.

Prediction of gas–water relative permeability in tight rock from movable fluid distribution with nuclear magnetic resonance

The measurement of the relative permeability in tight rock is challenging due to its ultralow permeability and the time-consuming nature of the experiments. Studying the movable and unmovable fluid distribution and establishing a reliable relative permeability prediction model is an urgent problem to be solved. This paper used nuclear magnetic resonance (NMR) to investigate movable and unmovable water distribution in tight sandstone under different centrifugal forces. A new method for predicting gas–water relative permeability in tight rock is established based on movable fluid distribution using the capillary bundle model. The results show that the distribution of movable and unmovable fluids is strongly influenced by the tight rock's pore size distribution and structure. The unmovable fluid saturation increases as the tight rock's permeability and median radius decrease. The nonlinear correlation between the NMR relaxation time and the pore throat size obtained from high-pressure mercury intrusion can be used to derive the pore size of the fluid distribution in tight rocks. The ratio of the movable fluid thickness to pore throat size increases near linearly with the logarithm of the pore throat size. The proposed mathematical model for the prediction of gas-water relative permeability based on movable fluid distribution is verified by comparing with the normalized relative permeability curve measured from experiments. This new model offers an alternative method of estimating the gas–water relative permeability when measurement is unavailable due to the ultralow permeability of the core samples.

Quantifying Magnetic Resonance Effects Due to Solid–Fluid Interactions on Confined Water within Quartz-Lined Nanopores via Molecular Dynamics Simulations

Nuclear magnetic resonance (NMR) relaxation time provides valuable information about properties of fluid and solid surfaces within rocks; however, the complexity of rock samples makes it difficult to quantify the effect of solid–fluid interactions on NMR measurements. Additionally, the ability of 2 MHz NMR equipment to probe nanopores is limited, while detailed analyses of fluid NMR properties in nanopores are possible through molecular dynamics (MD) simulations. We performed atomistic MD simulations to quantify the effect of solid–fluid interactions on confined water within hydroxylated slit and cylindrical quartz-lined rock pores (slit width and cylinder radius from 1 to 9 nm). NMR properties along with density profiles and mean-squared displacements (MSD) were calculated to quantify the effect of solids on relaxation times. MD results indicate that the surface chemistry of slit and cylindrical pores causes differences in density profiles and NMR properties of water confined in silica nanopores. Structural features present in density profiles are important to interpret both MSD and NMR relaxation properties. Intramolecular correlation times are shorter than intermolecular correlation times except when water is confined inside a 1 nm slit pore. These results highlight the importance of pore size on the solid–fluid interactions at the nanoscale. Layer analysis of confined water shows that NMR relaxation times of central layers in small nanopores are not the same as bulk relaxation time. This difference originates an overestimation of pore-size distributions of tight rocks from NMR measurements via Brownstein–Tarr’s equation. Furthermore, relaxation times of water layers indicate that the effect of solid surfaces on NMR relaxation times in a 3 nm slit pore is 15.32% of those in a 9 nm slit pore.

Solid state 1H, 7Li, and 13C NMR studies on new ionic plastic crystals of crown ether-Li-TFSA complexes.

This study provides the first evidence that a Li ion can form ionic plastic crystals using crown ether with a bis-(trifluoromethanesulphonyl) amide (TFSA) anion. 1H, 7Li, and 13C nuclear-magnetic-resonance (NMR) measurements of the 15-crown-5-Li-TFSA complex revealed that the constituents underwent isotropic reorientation in the plastic crystalline phase. The NMR data of the 12-crown-4-Li-TFSA salt showed that the complex is a rotator crystal (the complexes are denoted as [Li 15C5] and [Li 12C4] in this paper). The X-ray diffraction (XRD) reflection patterns of the [Li 15C5] crystal recorded in the highest-temperature solid phase (plastic phase) could be indexed to a cubic structure. Conversely, [Li 12C4] could be fitted to a trigonal structure. In this study, [M (3n)Cn] (M = Li, Na, K; n = 4-6) complexes were also prepared, and NMR, DSC, XRD, and electrical conductivity measurements were performed. Based on these results, we additionally revealed that the [Na 15C5] and [K (15C5)2] complexes are also new rotator crystals. Single-crystal XRD measurements also revealed that the [Na 15C5] compound has two stable sites in the crystal. Activation energies of molecular motions in the [M (3n)Cn] crystals were estimated using 1H NMR relaxation time (T1 and T2) measurements. The electrical conductivity measurements of [Li 12C4], [Li 15C5], and [Na 15C5] showed high ionic conductivities (∼10-2 S cm-1).

Nuclear magnetic resonance pore radius transformation method and fluid mobility characterization of shale oil reservoirs

The mobility of fluid is important for evaluating shale oil reservoirs, and it is closely related to the pore structure. Nuclear magnetic resonance (NMR) can effectively reveal the pore size distribution from nanometer to micron, providing a way to study the relationship between pore structure and mobility. However, the transverse relaxation time (T2) of NMR also contains bulk relaxation and diffusion relaxation, which will affect the accuracy of pore structure calculation. To characterize the mobility of shale oil by NMR, we proposed a pore radius transformation method with relaxation correction. The NMR simulations were carried out based on different digital core models, which were constructed according to X-CT results of shale cores. And the comparisons were performed to verified the accuracy and efficiency of the presented method. Then, the relation of geometric means of pore radius and mobility was studied through NMR experiments, and the NMR logging data of well J31 were processed by proposed method. The results show that the relative errors between corrected T2 distributions and surface relaxation distributions are smaller, and the geometric means of pore radius after relaxation correction are closer to those of digital core models, which proves the efficiency of the presented method. The logarithm of geometric mean of pore radius obtained from T2 distribution of shale core NMR experiment is positively correlated with S1/TOC, which can represent shale mobility. The processing results of NMR logging data in well J31 show two sections with large geometric means of pore radius, indicating that they have good mobility, which are consistent with the oil test results.

Dynamic NMR Relaxometry as a Simple Tool for Measuring Liquid Transfers and Characterizing Surface and Structure Evolution in Porous Media.

Porous media containing voids which can be filled with gas and/or liquids are ubiquitous in our everyday life: soils, wood, bricks, concrete, sponges, and textiles. It is of major interest to identify how a liquid, pushing another fluid or transporting particles, ions, or nutriments, can penetrate or be extracted from the porous medium. High-resolution X-ray microtomography, neutron imaging, and magnetic resonance imaging are techniques allowing us to obtain, in a nondestructive way, a view of the internal processes in nontransparent porous media. Here we review the possibilities of a simple though powerful technique which provides various direct quantitative information on the liquid distribution inside the porous structure and its variations over time due to fluid transport and/or phase changes. It relies on the analysis of the details of the NMR (nuclear magnetic resonance) relaxation of the proton spins of the liquid molecules and its evolution during some process such as the imbibition, drying, or phase change of the sample. This rather cheap technique then allows us to distinguish how the liquid is distributed in the different pore sizes or pore types and how this evolves over time; since the NMR relaxation time depends on the fraction of time spent by the molecule along the solid surface, this technique can also be used to determine the specific surface of some pore classes in the material. The principles of the technique and its contribution to the physical understanding of the processes are illustrated through examples: imbibition, drying or fluid transfers in a nanoporous silica glass, large pores dispersed in a fine polymeric porous matrix, a pile of cellulose fibers partially saturated with bound water, a softwood, and a simple porous inclusion in a cement paste. We thus show the efficiency of the technique to quantify the transfers with a good temporal resolution.

Quantifying the Effect of Spatial Confinement on the Diffusion and Nuclear Magnetic Resonance Relaxation of Water/Hydrocarbon Mixtures: A Molecular Dynamics Simulation Study

We implement molecular dynamics (MD) simulations to explore the relaxation mechanisms involved in the description of translational diffusion and rotational dynamics in water/hydrocarbon interfaces. The analysis of density profiles, self-diffusion coefficients, and nuclear magnetic resonance (NMR) relaxation properties as a function of the confinement layer width and type of hydrocarbons improves the understanding of confined water properties at water/oil interfaces. Density profile fluctuations reveal the presence of water-oil interactions close to the interface. MD results show that self-diffusion coefficients and NMR relaxation times of planar and cylindrical water/oil interfaces are strongly influenced by layer thickness and geometry. Shorter (between 20 and 60%) self-diffusion coefficients and 1H NMR relaxation times were obtained for water/n-pentane, water/n-decane, and water/n-hexadecane systems than bulk diffusion coefficients. An increase in Larmor frequency from 2.3 MHz to 400 MHz shows that longitudinal relaxation time (T1) of confined oil has slightly larger differences at higher frequencies than the transverse relaxation time (T2). At 400 MHz, n-alkanes (n-pentane, n-decane, and n-hexadecane) exhibit longer relaxation times than at smaller frequency values (2.3 and 22 MHz). Analysis of spin-spin and spin-lattice times provides relevant information about inter- and intramolecular relaxation mechanisms of water and oil as a function of geometry and width of the interface layer. These MD results suggest that the strength of confinement and geometry play a vital role in the diffusion and NMR relaxation properties of water/oil interfaces.