Low-field Nuclear Magnetic Resonance Relaxometry Research Articles

Using 1H low-field NMR relaxometry to detect the amounts of Robusta and Arabica varieties in coffee blends

Low-field nuclear magnetic resonance (LF-NMR) is a method of widespread use in food research due to its non-destructive character and the relatively low cost of the instruments, allowing the determination of oil / fat contents and the achievement of images of different types of food materials, among other uses. In this work, 1H LF-NMR relaxometry was used to distinguish the contributions due to Arabica and Robusta coffee varieties present in coffee blends. As the method detects preferentially the NMR signals due to phases with high molecular mobility, which exhibit longer values of the 1H transverse relaxation time (T2), the difference in the oil contents associated with Arabica and Robusta coffee was the key factor responsible for the detection of the contributions due to each variety. The analysis presented in this work showed that the relative hydrogen index is a useful parameter to be used in quantitative analyses of the contents of each coffee variety present in the blends. The results illustrate the high potential of applicability of LF-NMR relaxometry as a screening tool for quality control and adulteration detection of coffee-related products.

Structural Characterization of Several Cement-Based Materials Containing Chemical Additives with Potential Application in Additive Manufacturing.

The rapid increase in additive manufacturing applications in all industries has highlighted the lack of innovative technologies and processes in the construction industry. Several European and international policies are in place to guide the development of the technological processes involved in the construction industry toward a sustainable future. Considering the global concerns regarding this industry, the purpose of this study was to develop new cement-based materials that are capable of accelerated hydration and early strength development for use in additive manufacturing. Ca(NO3)2·4H2O, Al2(SO4)3·18H2O and Na2S2O3·5H2O were used to obtain the accelerating effect in the hydration of Portland cement. Based on results obtained from X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDX) techniques, as well as low-field nuclear magnetic resonance relaxometry (LF-NMR) techniques, it was demonstrated that all accelerators used have a quickening effect on cement hydration. The addition of Na2S2O3·5H2O or combined Na2S2O3·5H2O and Ca(NO3)2·4H2O led to obtaining new cement-based materials with early strength development and fast hydration of microorganized internal structures, critical characteristics for 3D printing.

Monitoring the Effect of Calcium Nitrate on the Induction Period of Cement Hydration via Low-Field NMR Relaxometry

The hydration process of Portland cement is still not completely understood. For instance, it is not clear what produces the induction period, which follows the initial period of fast reaction, and is characterized by a reduced reactivity. To contribute to such understanding, we compare here the hydration process of two cement samples, the simple cement paste and the cement paste containing calcium nitrate as an accelerator. The hydration of these samples is monitored during the induction period using two different low-field nuclear magnetic resonance (NMR) relaxometry techniques. The transverse relaxation measurements of the 1H nuclei at 20 MHz resonance frequency show that the capillary pore water is not consumed during the induction period and that this stage is shortened in the presence of calcium nitrate. The longitudinal relaxation measurements, performed at variable Larmor frequency of the 1H nuclei, reveal a continuous increase in the surface-to-volume ratio of the capillary pores, even during the induction period, and this increase is faster in the presence of calcium nitrate. The desorption time of water molecules from the surface was also evaluated, and it increases in the presence of calcium nitrate.

Investigations on asphaltene aggregate formation by high-field diffusion NMR and low-field ghost solvent NMR relaxometry

Aggregation of asphaltenes remains a scientific challenge. In the present contribution, at first, transverse magnetization relaxation (T2) data from low-field NMR measurements of the asphaltenes from heavy, medium-heavy, or light crude oil samples were recovered. Following this, diffusion ordered spectroscopy nuclear magnetic resonance (NMR) spectra of these asphaltenes were acquired to obtain average molecular weights (M w) of asphaltene aggregates. Analyzing the relaxation and diffusion behavior of asphaltene aggregates as a function of solution percentage and hence molecular weights are utilized to explain the difference between light, medium-heavy and heavy crude oil asphaltenes in aggregate formation. The main results suggest that light crude oil asphaltenes form a small but significant number of aggregates. In contrast, heavy crude oil asphaltenes demonstrate a more complicated picture at high concentrations with small, medium, and large aggregates. The relaxation behavior of medium-heavy asphaltenes is similar to those of heavy crude oil asphaltenes in diluted solutions and similar to light crude oil asphaltenes in concentrated solutions. Diffusion NMR results showed that the light crude oil asphaltene samples have a relatively smaller aggregate size, higher diffusion coefficient, and hence a smaller molecular weight than the samples extracted from heavy crude oils.

Characterization of the Influence of an Accelerator upon the Porosity and Strength of Cement Paste by Nuclear Magnetic Resonance (NMR) Relaxometry

Designing of new cement-based materials, suitable for three-dimensional printing applications, requires accurate control of the porosity and strength development. This goal may be achieved by introducing the so-called accelerators in the cement mixture. One such accelerator, used in many commercial products, is calcium nitrate. In the present work, the effect of calcium nitrate on the kinetics of pore evolution and strength development was investigated using low-field nuclear magnetic resonance relaxometry and compressive tests. The presence of calcium nitrate in cement paste accelerates the hydration dynamics immediately after mixing but does not significantly affect the pore structure. Moreover, the presence of calcium nitrate increases the compressive strength at 7 days compared with the simple cement paste but the same compressive strength was reached following 28 days of hydration.

1D magnetic resonance imaging and low-field nuclear magnetic resonance relaxometry of water-based silica nanofluids

The purpose of this research is to investigate 1-D Magnetic Resonance Imaging (MRI) and low-field Nuclear Magnetic Resonance (NMR) relaxation characteristics of silica nanofluids. The results show that presence of silica nanoparticles increases the MRI signal intensity and influences the NMR relaxation by shifting the relaxation peaks toward faster times compared to deionized water (DIW). Additionally, inversion recovery sequences show that nanoparticles reduce longitudinal relaxation time. For the tested nanofluid of EOR-12, signal intensity, longitudinal relaxation rate and transverse relaxation rate show a strong linear dependence on nanoparticle concentration with the highest enhancement of 1.75-fold, 2.57-fold and 3.20-fold, respectively compared to DIW. Additionally, investigation of the effect of nanoparticle size shows that below an optimal size, the MRI signal intensity and the NMR relaxation rates show a positive correlation with nanoparticle size but above the optimal size, the behavior reverses. For the nanoparticle with the optimal diameter, signal intensity, longitudinal relaxation rate and transverse relaxation rate enhancement was 2.21-fold, 4.44-fold and 4.45-fold, respectively compared to DIW. Application of the observed improvement in signal intensity to obtain the profile of the aqueous phase volume fraction in a Pickering emulsion shows a maximum error of 8% which indicates that the proposed technique can be applied for emulsion characterization with good accuracy.

Low-field 1H NMR relaxometry of water molecules confined in microporous UiO-66

Water molecules confined in a microporous metal–organic framework (MOF) UiO-66 are characterized by a low-field 1H nuclear magnetic resonance (NMR) spectroscopy. Measurements are performed of the longitudinal ([Formula: see text] and transverse ([Formula: see text] relaxation times as a function of water content from fully saturated to incomplete coverage of the first-adsorbed monolayer. The results obtained indicate that the relaxation of water molecules confined in UiO-66 is within the fast-exchange regime. When the amount of water exceeds filling ratio [Formula: see text] = 0.4, the averaged relaxation time is approximately linearly dependent on water filling ratio in pore. When the water amount cannot support a full coverage of surface monolayer, the relaxation rate increases with less filling ratio, illustrating that the mobility of water molecules is more restricted. Analysis of the measured values and the simulated ones leads to the conclusion that the surface-affected zone in UiO-66 is not confined to the surface monolayer.

Nuclear magnetic resonance analysis of water absorption characteristics and dynamic changes in pore size distribution of wood-plastic composites

Low-field nuclear magnetic resonance (NMR) technology was used to perform the experiments of transverse relaxation time (T2), pore size distribution, and water absorption rate for wood-plastic composites (WPC) with different contents of added slag powder, exploring the water movement and the dynamic changes of pore size during the moisture absorption process of the material under immersion condition. The experimental results were as follows: (1) According to the T2 of H proton and its inversion pattern, the measured porosity had a relatively small difference from that of the weighing method. (2) The pore size distribution graph showed the following: (i) when the immersion time of composite materials was different, the changing law of volume of pores with different radius was different.; (ii) when the material’s immersion time was greater than 216 h, the pore radius and its distribution characteristics showed large differences; (iii) slag powder changed the pore structure of the WPC but did not change the water absorption characteristics of the wheat straw. (3) The changes of water absorption and expansion rate showed that the slag powder changed the time for the materials’ pores to absorb water until saturation and reduced the water absorption and expansion rate. The measurement results were consistent with changing trend in the pore size obtained by low-field NMR relaxometry.

Application of Low-Field NMR to the Pore Structure of Concrete

In the present study, we used low-field nuclear magnetic resonance (LF-NMR) measurements and mercury intrusion porosimetry (MIP) to evaluate the influence of the water–binder (w/b) ratio, fly ash (FA) replacement and curing regimes on the pore structure of concrete. The main advantage of LF-NMR is that it is nondestructive and suitable for large concrete samples compared with other traditional methods, such as MIP, adsorption methods and scanning electron microscopy methods. Hence, the LF-NMR relaxometry method measures the pore structures that are closer to reality. The LF-NMR relaxation time, T2, represents the change in the pore structure during the hydration and hardening processes of concrete. The results showed that the T2 spectrum of the concrete sample was mainly composed of 3–5 signal peaks. Additionally, the w/b ratio, FA replacement and the curing regimes have significant effects on the T2 spectrum, porosity, and pore size distribution of concrete. In addition, the compressive strength of concrete has a close relationship with its pore structure. Based on the LF-NMR test results, the relationship between the compressive strength and the porosity, pore size distribution of concrete was established.

Cascading Mechanism Triggering the Activation of Polyphenol Oxidase Zymogen in Shrimp Litopenaeus vannamei After Postmortem and the Correlation with Melanosis Development

Melanization is the major deterioration in organoleptic quality of shrimp Litopenaeus vannamei during cold storage and leads to dramatical reduction of commercial value. So far, the biochemical cascade mechanism triggering and accelerating melanosis progression remains unclear. Herein, this investigation aimed to monitor the melanosis development in L. vannamei during 5 days’ cold storage at 4 °C and to explore the role of serine protease (SP) in zymogen activation of polyphenol oxidase (PPO) by application of low field nuclear magnetic resonance (LF-NMR), transmission electron microscopy (TEM), and immunohistochemistry (IHC). The results showed that melanosis development was positively associated with the increase of PPO and SP activities, and the utmost melanization was observed at cephalothorax segment, following with the telson and abdomen. Besides, LF-NMR relaxometry revealed both a dramatical reduction in trapped water component T22 and a significant increase in free water component T23. Meanwhile, the histopathological findings of hepatopancreas tissue demonstrated the progressive disruption in cytoarchitecture. Along with the increase of T23 and cytoarchitecture disruption, SP and Ca2+ were arbitrarily disseminated in hepatopancreas tissue. In addition, a heat map analysis revealed that there was a highly positive relationship between melanosis development and the aberrant elevation of PPO and SP activities, ratio of T22 components, cytoarchitecture disruption level, and dissemination status of SP and Ca2+. Altogether, the biochemical cascade events for melanosis development of L. vannamei during cold storage could be sketched out; i.e., the cytoarchitecture disruption, in combination with the driving force of free water molecule migration, was greatly favorable for aggregation of SP, Ca2+, and PPO zymogen, following with aberrant activation of PPO zymogen and initiation of melanization. These data provide new insights into the biochemical cascade mechanism of melanosis development in L. vannamei during cold storage and pave new ways for target controlling of melanization at initial stage.

Surface Area Determination of Kevlar Particles in Suspensions Containing Iron Impurities Using Low-Field Nuclear Magnetic Resonance Relaxometry

In the science and engineering of polymer matrix composites (PMC), the specific surface area of particle fillers is a key design consideration. In this study, the characterization of Kevlar pulp an...

Detecting Microbially Induced Calcium Carbonate Precipitation in Porous Systems Using Low-Field Nuclear Magnetic Resonance Relaxometry

Low-field nuclear magnetic resonance has been shown to be sensitive to the chemical and physical changes in a porous medium caused by microbially induced calcium carbonate precipitation (MICP), confirming its potential for detection of MICP for subsurface engineering applications. This investigation used a 2-MHz rock core analyzer, measuring T2 relaxation, in combination with scanning electron microscopy to characterize the daily chemical and physical changes occurring in various granular media including 1- and 0.5-mm soda lime glass beads and 1- and 0.45-mm quartz sand. An increase in T2 time was observed in all of the granular media in accordance with MICP progression. An estimate of the surface relaxivity, ρ, was obtained for the silica glass, quartz sand, and mineral precipitate, which allowed for correlation between mineral precipitation surface coverage and T2 relaxation time. The results indicated the potential for detailed in situ MICP progress monitoring during the early stages of the process by portable low-field nuclear magnetic resonance (NMR) devices.

Estimates of blood plasma water content using portable NMR relaxometry

Although blood plasma water content (PWC) is a relevant metric for many medical diagnostic procedures, the routine clinical measurement of PWC has remained elusive. Portable nuclear magnetic resonance (NMR) offers one way to nondestructively and quickly measure PWC. Contrived pseudoplasma samples that mimic blood plasma while also allowing rigorous control over water content are used to demonstrate the role of NMR in this work. Calibration curves relating measured NMR relaxation time constants (T2 and T1) to gravimetric PWC values for a set of human lyophilized plasma samples are used to predict the PWC in porcine and model human blood plasma from respective NMR T2 and T1 values. It is shown that the T2 and T1 decay constants measured with low field NMR relaxometry correlate with the PWC values for pseudoplasma and human lyophilized plasma samples. Statistical testing of the NMR-PWC correlation model demonstrated a prediction accuracy exceeding 98%. The PWC obtained in this way was used to correct sodium cation concentrations reported from direct ion-selective electrode tests. The accuracy of PWC determination with NMR is comparable to that of the gravimetric method that requires sample lyophilization. The rapid turnaround time, non-destructive nature, and portable footprint of the NMR-PWC measurement makes rapid, point-of-care clinical electrolyte estimates possible.

Capillary Trapping of CO2 in Sandstone Using Low Field NMR Relaxometry

AbstractInjecting carbon dioxide into geological formations for long‐term storage is considered integral to reducing greenhouse gas emissions. Residual trapping of CO2 is a primary storage mechanism, whereby CO2 ganglia are trapped in the pore space by capillary forces. Experimental knowledge of residual trapping processes in rocks is critical to the development of safe storage strategies. Here we present a quantitative low field 1H nuclear magnetic resonance (NMR) core flooding study of CO2 residual trapping in three different sandstones. It was found that transverse relaxation (T2) measurements were sensitive to the dissolution of paramagnetic ions from rock matrix minerals after exposure to carbonic acid; this response was observed on time scales relevant to core flooding experiments (i.e., minutes to hours). Subsequently, a brine aging protocol was designed and implemented to minimize this chemical effect, and hence, by applying the well‐known T2‐pore size relationship, changes in T2 time distributions during core flooding could be related to displacement of brine from pores of different sizes. Comparison of T2 distributions for partially CO2/brine‐saturated cores to previously published data for N2/H2O systems shows an increased displacement of brine from small pores by CO2. Furthermore, results from cyclical brine/CO2 injections showed an increase in the total volume of residually trapped CO2 and an increase in trapping efficiency; compared to the results observed for N2/H2O, however, the improvement in trapping efficiency with cyclic injection was less pronounced. Potential causes for the observed differences are discussed in the context of effective N2 and CO2 wetting.

In-situ heavy oil viscosity prediction at high temperatures using low-field NMR relaxometry and nonlinear least squares

Heavy oil and bitumen resources are the most abundant hydrocarbon energy source worldwide. However, due to their high viscosity, complex thermal enhanced oil recovery (EOR) methods are frequently applied to reduce it. Information about the distribution of oil viscosity within the reservoir can be used to help management of thermal EOR project. Nuclear magnetic resonance (NMR) downhole tools provide a non-destructive way to determine the oil viscosity without having to recover samples (core or produced oil) from the wellbore. Tests showed that the accuracy of the literature NMR viscosity models significantly decreases with temperature increase, making them ineffective for monitoring high temperature. Moreover, improved accuracy is required for high viscosity ranges of oil representative of original reservoir conditions.An enhanced NMR viscosity model was developed and tested on a suite of 23 Canadian heavy oils recovered from different reservoirs. Subsequently, the model was tested on a single bitumen sample at temperature range 26–200 °C. Results were compared to nine well-known NMR viscosity models from the literature, and in both cases, the enhanced model scored the lowest root mean square error (RMSE) in this study. Furthermore, a simple model optimization procedure was presented, which employs nonlinear least squares (NLS) regression.Experiments were carried out at the temperatures that correspond to those in the hot steam injection EOR treatments. The same methodology can be extended for use in cyclic solvent injection (CSI) where NMR model can detect the change of oil viscosity when the solvent vapor dissolves into the oil.

Low field NMR relaxation as a probe to study the effect of activators and retarders on the alkali-activated GGBFS setting process

Low field nuclear magnetic resonance relaxometry (LF-NMR) was used to study the setting process of alkali-activated GGBFS (AA-GGBFS) paste during the early curing hours. LF-NMR measurements were carried out from fresh paste casting until hardening (generally no more than 8 h). The transverse relaxation time T2 was used as a probe to assess the setting process. Combined with Vicat penetration and temperature monitoring, an important threshold indicator was defined as the deadline for paste casting (DPC). The physical meaning of the DPC is a threshold point where the developing micro pores make loss of movable water attain a certain level so that the semi-solid paste has slight strength. Moreover, several periods related to AA-GGBFS early-hour paste development are proposed: (1) dissolution; (2) setting; (3) acceleration; and (4) hardening. By analysing each period during the early hours, it was found that the hybrid retarder of zinc nitrate and sodium gluconate works for the AA-GGBFS system.

Study of Aliphatic Polyurethanes by the Low-Field 1H NMR Relaxometry Method with the Inversion of the Integral Transformation

In this paper, the distributions of the 1H nuclear magnetic resonance (NMR) spin–lattice and spin–spin relaxation times are used to characterize the mobility of different sections of macromolecules of aliphatic polyurethanes and the cross-linking density of polymer chains. The NMR relaxometry method with inversion of integral transformation is applied to study the effect of poly (ethylene glycol) and glycerol phosphate calcium on the polymer dynamics.

Leaf Development Monitoring and Early Detection of Water Deficiency by Low Field Nuclear Magnetic Resonance Relaxation in Nicotiana tabacum Plants

Drought is the main abiotic stress worldwide affecting harvest quality and quantity of numerous crops. To enable better water management, low field NMR (nuclear magnetic resonance) relaxometry was assessed as a developmental marker and a new method for early detection of water deficiency. The effect of a foliar biostimulant against water stress was also investigated. Two leaves of different ranks (four and eight) were studied. The leaves of different ranks were characterized by different NMR T2 spectra which validated the ability of NMR to describe the developmental stage of tobacco. Results also showed that T2 NMR relaxation spectra allow the detection of mild water stress (80% of the field capacity) through the precise characterization of the leaf water status while other water stress markers (relative water content, photosynthetic related parameters…) were not yet impacted. The agricultural impact of the mild water stress was determined through the nitrogen rate in shoots and amino acids assay six weeks after the beginning of the stress and results shows that foliar application of biostimulant limits the negative consequences of drought. Our results demonstrate the sensitivity of NMR to detect slight changes triggered in the leaf by water stress at the tissue level.

Measuring hydrological connectivity inside a soil by low field nuclear magnetic resonance relaxometry

AbstractHydrological connectivity inside the soil is related to the spatial patterns inside the soil (i.e., the structural connectivity). This, in turn, is directly associated with the physical and the chemical processes at a molecular level (i.e., the functional connectivity). Nuclear magnetic resonance (NMR) relaxometry can be successfully applied to reveal both structural and functional components of soil hydrological connectivity. In the present study, the low field NMR relaxometry was applied on water suspended soils sampled at the upstream‐ and downstream‐end of three different length plots. Also the sediments collected from the storage tanks at the end of each plot were water suspended and monitored by NMR relaxometry. The results from the NMR investigations were elaborated by using a mathematical approach in order to quantify both the functional and structural connectivity components. In particular, following integration of the T1 distribution curve, an S‐shaped curve was obtained. It revealed two plateaus corresponding to the shortest (low component) and the longest (high component) intervals of relaxation times, respectively. According to relaxometry theory, the two T1 intervals, associated to the different plateaus, were attributed to micro and macro soil pores, respectively. The two T1 intervals were used to define a functional connectivity index, while the central part of the S‐shaped distribution was used to define a structural connectivity index. Here we provide the physical meaning of the our mathematical approach, thereby revealing that functional connectivity index increases with plot length, as a result of a selective eroded particle transport. Moreover, the relationship structural connectivity index versus plot length resulted quasi‐independent of grainsize distribution, whereas the values of the structural connectivity index for the sediment samples resulted lower than those obtained for the corresponding soils.

Probing into the mesoporous structure of carbon xerogels via the low-field NMR relaxometry of water and cyclohexane molecules

The liquid morphology of water and cyclohexane molecules, under partially saturated conditions inside the porous structure of two mesoporous carbon xerogels, was investigated using low-field nuclear magnetic resonance (NMR) relaxometry. The two xerogels were prepared under the same conditions, but with a different resorcinol-to-catalyst ratio. Two techniques were used in our investigations: the well-known Carr–Purcell–Meiboom–Gill (CPMG) pulse sequence for transverse relaxation measurements and the Fast Field-Cycling (FFC) relaxometry technique for longitudinal relaxation dispersion measurements. It was found a stronger interaction of cyclohexane molecules with the pore surface as compared with water molecules. This leads to a uniform coverage of cyclohexane molecules on the pore surface for lower filling degrees while, in the case of water filled carbon xerogels, the distribution was non-uniform. Due to the stronger adsorption of cyclohexane molecules on the pore surface, it was possible to identify the micropores of the carbon xerogels predicted by nitrogen adsorption data. The NMR relaxation data have clearly demonstrated that, by increasing the resorcinol-to-catalyst ratio, the size of mesopores increases. Moreover, the enhanced adsorption affinity of carbon xerogels for cyclohexane shows that this type of materials can be employed as adsorbents for the removal of similar organic contaminants from water.