Investigation of oil and water migrations in lacustrine oil shales using 20 MHz 2D NMR relaxometry techniques

The behavior of oil and water in tight rocks can change the distribution of oil or water in pores,which affects the production of crude oil.Nuclear Magnetic Resonance(NMR)method is an effective and nondestructive tool for evaluating rocks with comparison and analysis both quantitatively and qualitatively.In our study,20 MHz NMR Relaxometry is used as a key technique to study the changes of water and oil behaviors in Chinese lacustrine Qingshankou shales under different saturated states(imbibition and evaporation without pressure).The results show that variation in different proton populations(water,oil and organic)can be distinguished using 2D T_(1)-T_(2)maps.The comparison among T_(1)-T_(2)maps with different saturated states shows that different signal regions changed during oil and water migrations,which the 1D NMR Relaxometry may be not easy to approach.Combined with the pyrolysis analysis,T2 shift and differences of signal regions in T_(1)-T_(2)maps can reflect properties such as wettability and composition(organic matter,clay and magnetic minerals)to some extent.This study provides better insight into oil and water behaviors in lacustrine oil shales with further understanding of 20 MHz NMR 2D T_(1)-T_(2)maps both in qualitative and quantitative analysis.

Monitoring Cr(Ⅵ)photoreduction at different depths by operando low-field NMR relaxometry

Chromium(VI)(Cr(VI)),a toxic metal ion,is widely present in industrial wastewater.To reduce the contamination of Cr(VI),many technologies for the photocatalytic reduction of Cr(VI)to Cr(III)have been developed in the past decades.However,the practical application of photocatalysts for the reduction of Cr(VI)inwastewater treatment is often hindered by the complicated photoreduction processes due to the sedimentation and stratification of catalyst particles that present during the treatment of the wastewater.Probing and understanding the influences of the sedimentation and stratification of the catalyst particles on the photoreduction processes are long-term challenges in the field.Herein,we demonstrate that this issue can be solved by using layer location integrated low-field time-domain nuclear magnetic resonance(LF-NMR)relaxometry.With paramagnetic Cr(III)cation as the molecular probe,we successfully monitored the Cr(VI)photoreduction processes by operando probing the 1 H T2 relaxation time of the photoreduction systems.The influences of catalyst sedimentation and the light wavelength on photocatalysis were studied and discussed.The results showed the great potential of LF-NMR relaxometry in the study of Cr(VI)photoreduction processes during industrial wastewater treatments.

Thalamic paramagnetic iron by T2＊ relaxometry correlates with severity of multiple sclerosis

Iron can contribute to the pathogenesis and progression of multiple sclerosis（MS） due to its accumulation in the human brain.We focus on the thalamus as an information transmitter between various subcortical and cortical areas.Thalamic iron seems to follow different rules than iron in other deep gray matter structures and its relation to the clinical outcomes of MS is still indistinct.In our study,we investigated a connection between thalamic iron and patients＇ disability and course of the disease.The presence of paramagnetic substances in the tissues was tracked by T2＊ quantification.Twenty-eight subjects with definite MS and 15 age-matched healthy controls underwent MRI examination with a focus on gradient echo sequence.We observed a non-monotonous course of T2＊ values with age in healthy controls.Furthermore,T2＊ distribution in MS patients was significantly wider than that of age matched healthy volunteers（P〈 0.001）.A strong significant correlation was demonstrated between T2＊ distribution spread and the expanded disability status scale（EDSS）（left thalamus：P〈0.00005;right thalamus：P〈0.005）,and multiple sclerosis severity scale（MSSS）（left thalamus：P〈0.05;right thalamus：P〈0.005）.The paramagnetic iron distribution in the thalamus in MS was not uniform and this inhomogeneity may be considered as an indicator of thalamic neurodegeneration in MS.

Application of NMR Relaxometry to Study Nanostructured Poly(vinyl alcohol)/MMT/Cephalexin Materials for Use in Drug Delivery Systems

Polymers containing nanoparticles dispersed and distributed in the matrix can be used for control of drug release. In this work, hydrophilic matrix systems were prepared using poly(vinyl alcohol) and unmodified clay containing the same amount of cephalexin. The materials were obtained through in situ polymerization and were characterized by the conventional technique of FTIR and NMR relaxometry, through determination of proton spin-lattice relaxation time, in order to understand the molecular behavior of the new materials. The NMR relaxometry data showed that the new materials containing low quantities of clay (0.25% and 0.75%) and the same amount of cephalexin (0.5 g) had very good dispersion and distribution of the clay and drug in the polymer matrix. The combination of clay and cephalexin formed a more homogenous material with a narrow domain curve and low relaxation values. The material containing 0.25% clay presented a mixed morphology, with part exfoliated and part intercalated, as could be seen from the relaxation domain distribution, which was larger than that for material with 0.75% clay.

Selective coordination and localized polarization in graphene quantum dots: Detection of fluoride anions using ultra-low-field NMR relaxometry

The development of ultra-sensitive methods for detecting anions is limited by their low charge to radius ratios, microenvironment sensitivity, and p H sensitivity. In this paper, a magnetic sensor is devised that exploits the controllable and selective coordination that occurs between a magnetic graphene quantum dot(GQD) and fluoride anion(F–). The sensor is used to measure the change in relaxation time of aqueous solutions of magnetic GQDs in the presence of F–using ultra-low-field(118 μT) nuclear magnetic resonance relaxometry. The method was optimized to produce a limit of detection of 10 nmol/L and then applied to quantitatively detect F–in domestic water samples. More importantly, the key factors responsible for the change in relaxation time of the magnetic GQDs in the presence of F–are revealed to be the selective coordination that occurs between the GQDs and F–as well as the localized polarization of the water protons. This striking finding is not only significant for the development of other magnetic probes for sensing anions but also has important ramifications for the design of contrast agents with enhanced relaxivity for use in magnetic resonance imaging.

Dipolar NMR relaxation of adsorbates on surfaces of controlled wettability

In reservoir rocks,the term“ageing”refers to extended exposition to crude oil;a typically water-wet sandstone will then gradually become oil-wet as a consequence of the deposition of insoluble fractions of oil onto the surface grains.Rocks have been aged artificially by subjecting them to a bitumen solution at elevated temperature in order to achieve comparable surface properties for three different types of rock:Bentheimer,Berea Buff and Liege Chalk.Using saturated and aromatic model compounds as proxies for crude oil,the nuclear magnetic resonance(NMR)relaxation dispersion in native and aged rocks was compared and correlated to the properties of paramagnetic impurities in these rock types.Perfluorated liquids were found to follow the same trend as deuterated and naturally occurring oil components,suggesting they can be used as suitable tracers for wettability studies since the ^(19)F nucleus is absent in natural sources.By combining electron paramagnetic resonance(EPR)and dynamic nuclear polarization(DNP)it becomes possible to identify and quantify the origin of the dominating relaxation processes between native and aged rocks,providing an alternative approach to assess wettability in natural rocks.

Study on Multi-Exponential Inversion Method for NMR Relaxation Signals with Tikhonov Segularization

The analysis of NMR data in terms of inversion of relaxation distribution is hampered by the ill-posed nature of the required solution about the Fredholm integral equation. Naive approaches such as multi-exponential fitting or standard least-squares algorithms are numerically unstable and often failed. This paper updates the application of Tikhonov regularization to stabilize this numerical inversion problem and demonstrates the method for automatically choosing the optimal value of the regularization parameter. The approach is computationally efficient and easy to implement using standard matrix algebra techniques, which is based on mathematical ware MATLAB. Example analyses arepresented using both synthetic data and experimental results of NMR studies on the liquid samples like as oils and yoghurt.

Influence of Organoclay Structure on Nanostructured Materials Based on Eva

This article reports the preparation of a series of EVA nanocomposites employing solution casting methods using different types of organo-modified montmorillonite clay. The effect of the organoclay type on the structural organization and thermal behavior of EVA nanostructured materials were systematically investigated. Regarding thermal behavior, the thermogravimetric analysis showed that the nanocomposites presented a slight decrease in thermal degradation temperature compared to EVA, while differential scanning calorimetry, in general, did not show a significant change in the thermal transition temperatures such as glass transition, melting temperature and crystallization temperature of the nanocomposites, regardless of the type and proportion of organoclay in the systems. With respect to structural aspect, the X-ray diffractograms showed that all systems presented a heterogeneous distribution of the nanoparticles, containing part intercalated. Nuclear magnetic resonance relaxometry data provided complementary information for the X-ray results, showing that the EVA systems containing 5 wt% of both studied organoclays presented a mixture of intercalated and exfoliated structures, evidencing that there was a surface interaction between polymer chains and clay lamellae.

The Development and Characterization of Polycaprolactone and Titanium Dioxide Hybrids

Organic/Inorganic hybrid materials have been attracting much attention since they combine the advantages of inorganic materials with the properties of organic polymers. Titanium dioxide nanoparticles (TiO2) present good thermal stability, accessibility and catalytic properties. Polycaprolactone (PCL) is a bi-ocompatible and bioresorbable material, which is being examined as biode-gradable packaging materials, controlled drug release carriers and other medical applications. Hybrids based on PCL containing different amounts of titanium dioxide nanoparticles, ranging from 0.05% to 0.35% w/w, were prepared using the solution cast method. These systems were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), low-field nuclear magnetic resonance (NMR), thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The FTIR analysis confirmed that there was an interaction between the PCL chains and the TiO2 nanoparticles. The XRD and DSC analysis showed that the PCL crystallization was affected by TiO2 incorporation, modifying its semi-crystalline structure to a less ordered structure. When TiO2 nanoparticles were added the values of T1H and T1ρH increased for all hybrids, therefore, their addition produced a new material with less molecular mobility. In the TG analysis, it was observed that the introduction of TiO2 nanoparticles decreased the thermal resistance of PCL. In DSC analysis, the PCL/TiO2 hybrids presented a reduction in the crystallization temperature and degree of crystallinity, except for PCL hybrids containing 0.15% w/w of TiO2 nanoparticles.

Spin-Spin Relaxation Time to Evaluate Degradation of HIPS/Organoclaynano Composites by Aging

NMR relaxometry is one of the techniques that allow observing changes in the molecular mobility that come from materials’ morphology. T1H has been used to monitor food and polymer sciences. However, T2>H, although being a revealing as T1>H, is rarely used to analyze changes in thermoplastic systems it is more sensitive to the mobile region. High Impact Polystyrene nanomaterials were prepared through solution casting and were exposed for different times to UV light in the air. The samples, removed after each exposure interval, were characterized by T2>H, focusing on the changes in the relaxation data. The results for this parameter showed that the changes in the relaxation data come from the competition of chain scission and chain recombination processes, which occurs due to the UV light influence with increased time. The T2>H data indicated that the clay ratio can influence the chain degradation processes, acting to inhibit or accelerate the aging process [1] [2].