1H Nuclear Magnetic Resonance Relaxometry Research Articles

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.

Moisture sorption behaviour, microstructural changes and macroscopic deformation of hardened cement pastes during the first three drying–resaturation cycles

Moisture sorption and macroscopic deformation of hardened cement pastes (hcps) were studied in the first three drying–resaturation (D–R) cycles using low–field 1H nuclear magnetic resonance relaxometry. Four types of water (interlayer, gel, interhydrate and capillary) were detected in the hcps. In principle, they were sequentially removed from larger to smaller pores during drying with decreasing relative humidity (RH), resulting in shrinkage of the hcps. Unexpected increases in gel and interlayer water contents as well as greater shrinkage during drying from 100 % to 69 % RH were observed, which is believed to originate from the re–arrangement of C–S–H structure. Because of the C–S–H re–arrangement, irreversible shrinkage was detected during D–R cycles. The drying and irreversible shrinkage in each cycle diminished with the D–R number. A lower water–to–cement ratio and higher curing temperature for hcps are beneficial for reducing drying and irreversible shrinkage.

Microscopic and Macroscopic Characterization of Hydrogels Based on Poly(vinyl-alcohol)-Glutaraldehyde Mixtures for Fricke Gel Dosimetry.

In recent decades, hydrogels have emerged as innovative soft materials with widespread applications in the medical and biomedical fields, including drug delivery, tissue engineering, and gel dosimetry. In this work, a comprehensive study of the macroscopic and microscopic properties of hydrogel matrices based on Poly(vinyl-alcohol) (PVA) chemically crosslinked with Glutaraldehyde (GTA) was reported. Five different kinds of PVAs differing in molecular weight and degree of hydrolysis were considered. The local microscopic organization of the hydrogels was studied through the use of the 1H nuclear magnetic resonance relaxometry technique. Various macroscopic properties (gel fraction, water loss, contact angle, swelling degree, viscosity, and Young's Modulus) were investigated with the aim of finding a correlation between them and the features of the hydrogel matrix. Additionally, an optical characterization was performed on all the hydrogels loaded with Fricke solution to assess their dosimetric behavior. The results obtained indicate that the degree of PVA hydrolysis is a crucial parameter influencing the structure of the hydrogel matrix. This factor should be considered for ensuring stability over time, a vital property in the context of potential biomedical applications where hydrogels act as radiological tissue-equivalent materials.

Multiple effects of glycine on stability and rheology behavior of hydrated Mg(OH)2 slurry

Hydration of MgO is a potential technology for economically preparing Mg(OH)2 slurry. Understanding the rheological behavior evolution of the slurry during MgO hydration, particularly in the presence of hydration agent, is essential for better control of the hydrated Mg(OH)2 slurry’s rheology. In this work, Mg(OH)2 slurry was prepared by hydrating MgO in the presence of glycine. The effect of glycine on the rheological behavior of the hydrated Mg(OH)2 slurry have been investigated by means of viscosity, shear stress, sedimentation measurements, particle size distribution, 1H nuclear magnetic resonance relaxometry and zeta potential. Results showed that shear thinning rheological slurry could be made by hydration at 80 °C for 1 h. The yield stress of the slurry is 27.49 ± 0.81 Pa, and no settling occurs within 7 days. Yet, in the absence of glycine, the structure of the slurry was unstable and easily settled even after 8 h of hydration. Glycine has multiple effects on the slurry’s solid loading, particle morphology, particle size distribution, and zeta potential of the slurry. In addition, the neutral zwitterionic form of glycine may serve as an inter-particle lubricant, reducing viscosity.

Structural integrity and healing efficiency study of micro-capsule based composite materials via 1H NMR relaxometry

In this work we present a novel approach utilizing nuclear magnetic resonance (NMR) relaxometry to assess the structural stability of microcapsules employed as self-healing agents in advanced aerospace composites both in ambient and harsh environmental conditions. We successfully correlate the amount of the encapsulated self-healing agent with the signal intensity and confirm non-destructively the quantity of the encapsulated self-healing agent mass for the first time in the literature using 1H NMR spin–spin relaxation techniques on urea–formaldehyde (UF) microcapsules of different diameters containing an epoxy healing agent. The amount of self-healing agent is shown to increase by reducing the capsule diameter; however, the reduced shell mass renders the capsules more fragile and prone to failure. Most notably, via NMR experiments conducted during thermal cycling simulating flight conditions, we demonstrate that the microcapsule integrity under thermal fatigue varies according to their size. Especially we experimentally verify that the microcapsules with the most sensitive shells are the 147 nm and 133 nm diameter microcapsules, which are the most commonly used in self-healing systems. Finally, we were able to retrieve the same results using a portable NMR spectrometer developed in-house for in situ microcapsule testing, thus demonstrating the potential of NMR relaxometry as a powerful non-destructive evaluation tool for the microcapsule production line.

Time Domain NMR Approach in the Chemical and Physical Characterization of Hazelnuts (Corylus avellana L.).

'Tonda Gentile Romana' and 'Tonda di Giffoni' (Corylus avellana L.) are two Italian hazelnut cultivars, recognized under the quality labels "Protected Designation of Origin" (PDO) and "Protected Geographical Indication" (PGI), respectively. Hazelnut seeds are characterized by a complex microstructure and the presence of different physical compartments. This peculiarity has been studied and evidenced by Time Domain (TD) Nuclear Magnetic Resonance (NMR) experiments. This technique allowed the assessment of the presence of different diffusion compartments, or domains, by evaluating the distribution of the spin-spin relaxation time (T2).The aim of this research was to develop a method based on 1H NMR relaxometry to study the mobility in fresh hazelnut seeds ('Tonda di Giffoni' and 'Tonda Gentile Romana'), in order to determine differences in seed structure and matrix mobility between the two cultivars. TD-NMR measurements were performed from 8 to 55 °C in order to mimic post-harvest processing as well the microscopic textural properties of hazelnut. The Carr-Purcell-Meiboom-Gill (CPMG) experiments showed five components for 'Tonda Gentile Romana' and four components for 'Tonda di Giffoni' relaxation times. The two slowest components of relaxation (T2,a about 30-40% of the NMR signal, and T2,b about 50% of the NMR signal) were attributed to the protons of the lipid molecules organized in the organelles (oleosomes), both for the 'Tonda Gentile Romana' and for the 'Tonda di Giffoni' samples. The component of relaxation T2,c was assigned to cytoplasmic water molecules, and showed a T2 value dominated by diffusive exchange with a reduced value compared to that of pure water at the same temperature. This can be attributed to the water molecules affected by the relaxation effect of the cell walls. The experiments carried out as a function of temperature showed, for 'Tonda Gentile Romana', an unexpected trend between 30 and 45 °C, indicating a phase transition in its oil component. This study provides information that could be used to strengthen the specifications underlying the definitions of "Protected Designation of Origin" (PDO) and "Protected Geographical Indication" (PGI).

Deformation mechanisms of cement paste with ultra-low water-to-cement ratios under different curing conditions at early ages

Cement-based materials with ultra-low water-to-cement ratios (w/c) swell with external water supply, which may cause cracking and strength reduction. Studies on the volumetric stability of cement-based materials ignore the possible expansion occurring in the material before the starting point, standard curing (20 ± 2 ℃ and relative humidity (RH) > 95 %) for 28 d. Thereby, the deformation and mechanical properties of cement paste cured under standard and sealed conditions at early ages were compared. Deformation mechanisms were investigated by thermogravimetric analysis, 1H nuclear magnetic resonance relaxometry, and pore structure measurement. The saturation degree and hydration degree were both estimated. The results show that swelling occurs in cement-based materials with ultra-low w/c under standard curing, with increasing flexural and compressive strength. Gel water and capillary water contribute to large proportions of the total absorbed water. Cement paste with low w/c produces higher swelling when absorbs the same amount of water. Deformation mechanisms are attributed to the mitigation of self-desiccation shrinkage, calcium-silicate-hydrate gel swelling due to water absorbed, and solid volume increase of solids after hydration.

Response of water-biochar interactions to physical and biochemical aging

Biochar aging may affect the interactions of biochar with water and thus its performance as soil amendment; yet the specific mechanisms underlying these effects are poorly understood. By means of FTIR, N2 adsorption, Hg intrusion porosimetry, thermogravimetric analysis, 13C solid state nuclear magnetic resonance (NMR) and 1H NMR relaxometry, we investigated changes in the chemistry and structure of biochar as well as its interaction with water after biochar aging, both physical (simulated by ball-milling) and biochemical (simulated by co-composting). Three different porosities of biochar were examined: <5 nm, 1 μm and 10 μm diameter sizes. Physical aging caused the disappearance of the porosity at 10 μm. With biochemical aging, biochar underwent an enrichment of oxygenated functional groups either as a result of surface functionalisation processes or by the deposition of fresh organic matter layers on the surface and pores of biochar. 1H NMR relaxometry revealed that the proportion of water strongly interacting with biochar increased with both physical and biochemical aging. Although biochemical aging significantly altered the composition of biochar surface and modulates its interaction with water, 1H NMR relaxometry proved that physical aging had a relatively stronger influence on water mobility and dynamics in biochar, lowering both T1 and T2 relaxation times in the initial contact times of biochar and water.

Investigation of 1H nuclear magnetic resonance relaxometry to screen metabolic syndrome and diabetes.

The purpose of this study was to investigate and compare the abilities of 1H nuclear magnetic resonance (NMR) transverse relaxation constant time (T2) and longitudinal relaxation constant time (T1) to screen people at the risk of diabetes and metabolic syndrome. Human blood samples were collected for NMR detection and biochemical examinations. Bivariate correlations, categorical analyses were performed to explore the relationship between NMR relaxation time and metabolic biomarkers. Results show that NMR relaxation time of human serum correlated well with some biomarkers associated with diabetes and metabolic syndrome. Statistically significant differences in NMR relaxation time between subjects with normal and poor metabolic health were observed. NMR relaxation time, especially T2, can be used to screen people at risk of diabetes and metabolic syndrome.

The Physical Stability of Felodipine and Its Recrystallization from an Amorphous Solid Dispersion Studied by NMR Relaxometry.

The 1H nuclear magnetic resonance (NMR) relaxometry method was applied to investigate the physical stability of an active pharmaceutical ingredient (API) and, for the first time, its recrystallization process in an amorphous solid dispersion system (ASD). The ASD of felodipine and polyvinylpyrrolidone (PVP) was prepared using the solvent evaporation method in a mass ratio of 50:50. In the first stage of the study (250 days), the sample was stored at 0% relative humidity (RH). The recovery of magnetization was described by one-exponential function. In the second stage (300 days in 75% relative humidity), the recrystallization process of felodipine was studied, showing in the sample three components of equilibrium magnetization related to (i) crystalline felodipine, (ii) water, and (iii) felodipine and PVP remaining in the ASD. The study shows that the 1H NMR relaxometry method is a very useful tool for analysing the composition of a three-phase system mixed at the molecular level and for the investigation of recrystallization process of API in amorphous solid dispersion system.

The contribution of microbial activity to soil–water interactions and soil microstructural stability of a silty loam soil under moisture dynamics

Soil structure and its stability against external stresses is fundamental to various soil functions and ecosystem services. Particularly soil moisture dynamics and microbial activity can affect soil structure by promoting particle reorientation, cementation and spatio-temporal pore space remodeling. In this context, microbial exudates can serve as interparticulate binding agents and thus contribute to the formation of stable soil structures and basic physico-chemical soil properties. However, detailed interactions and relationships between microbial activity, soil pore water and the porous soil matrix itself are still unclear, especially in the context of dynamic moisture conditions. In this study, we aimed to increase the fundamental understanding of microbially-induced and moisture dynamic-affected soil microstructural stability and soil–water interactions. For this, a sterilized, untreated and substrate-enhanced silty loam soil was subjected either to constant moisture conditions or four consecutive drying-wetting cycles. At defined timepoints, soil samples were investigated for carbon dioxide release (respirometry), phospholipid fatty acid analysis, wetting behaviour (contact angle), rheological characteristics (rheometry) and water entrapment (1H nuclear magnetic resonance relaxometry) to respectively determine microbial activity, community structure and biomass, soil wettability, soil microstructural stability and the frequency distribution of water-filled pore sizes in soil (FDWPS). Results showed that substrate enhancement promoted soil microstructural stability compared to sterilized and untreated soil, whereby all soils reacted dynamically and irreversibly to the adjusted moisture conditions. Significant positive correlations were found between microbial activity, wettability, FDWPS and soil microstructural stability, which indicate that the presence of interparticulate microbial structures augmented the spatio-temporal reorganization effect induced by soil moisture dynamics. The irreversible dehydration of those interparticulate microbial structures resulted in an additional pore space cementation, water redistribution to smaller soil pores and thus a considerably increased microstructural stability due to stronger cohesive and capillary forces. The results help to understand the extent to which soil moisture dynamics can modulate microbial-induced soil processes and basic soil properties.

Field-cycling 31P and 1H NMR relaxometry studying the reorientational dynamics of glass forming organophosphates.

We apply field-cycling (FC) 31P nuclear magnetic resonance (NMR) to access the reorientational susceptibility of two glass formers, m-tricresyl phosphate (m-TCP) and tri-butyl phosphate (TBP). Although FC 31P studies are still instrumentally demanding, together with FC 1H data, they provide site-resolved information. A crossover from dipolar relaxation at low frequencies to relaxation determined by chemical shift anisotropy at high frequencies and probed by conventional NMR is identified. A comparison is made between dielectric (DS) and depolarized light scattering (DLS) relaxation spectra demonstrating similar behavior close to Tg, including an excess wing contribution for m-TCP. The time constants of 31P NMR and DLS, probing the molecular core, agree. The 1H data monitoring the dynamics of the phenyl groups yield slightly shorter correlation times. At high temperatures, the DS relaxation spectra show a bimodal character: a fast component in agreement with 1H data, and a slow component much slower than 31P NMR and DLS suggest. We discuss the possible origins of the slow component. All time constants tend to merge toward Tg. Hence, we propose that site-specific dynamics disappear and a common α-relaxation establishes near Tg. In addition, we compare the diffusion coefficient D(T) determined by FC and static field gradient 1H NMR. Concerning TBP, we present FC 31P data of both α- and β-processes. Regarding the latter, we compare the DS and NMR susceptibility on absolute scale, yielding a significantly stronger β-relaxation in the 31P NMR spectra.

Low-field 1H NMR parameterization of model cell suspensions. A diffusion and relaxation study.

Nuclear magnetic resonance (NMR) is a powerful method for the non-invasive study of a wide range of objects. Among its many characteristics, molecular diffusion can be examined without the need for any chemical or isotopic tracers by applying magnetic field gradients within the NMR sequence. In our study, model cell suspensions were characterized by means of low-field (LF) (0.05 T) 1H NMR relaxometry. The proposed multi-parametric characterization based on independent 2D T1-T2 and D-T2 measurements was implemented to obtain a set of MR parameters as a specific signature for model cells. The D-T2 and T1-T2 correlation measurements were conducted on yeast samples with different amounts of added water. Signals from intracellular and extracellular water compartments and free water were identified on D-T2 maps and their diffusion coefficients were extracted. Mean D_IC was equal to 8.4 × 10-11 m2/s and mean D_EC ranged from 1.0 × 10-9 m2/s to 1.65 × 10-9 m2/s. T1/T2 ratio was calculated and for IC space values in the range of 4.2-5.3 were observed. Finally, we demonstrated the possibility of detecting signals from cells for the samples with a low concentration of cell suspensions or a small amount of the sample. These findings are promising for more complex cell investigations in vitro and in vivo, without any contrast agents, applying solely biomarkers.

Kinetics of Resorcinol-Formaldehyde Condensation-Comparison of Common Experimental Techniques.

Porous carbons, originated from resorcinol-formaldehyde (RF) gels, show high application potential. However, the kinetics and mechanism of RF condensation are still not well described. In this work, different methods (dynamic light scattering–DLS, Fourier transform infrared spectroscopy–FTIR, low field 1H nuclear magnetic resonance relaxometry–1H-NMR, and differential scanning calorimetry–DSC) were used to follow the isothermal RF condensation of mixtures varying in catalyst content (Na2CO3) and reactant concentration. The applicability and results obtained by the methods used differ significantly. The changes in functional groups can be followed by FTIR only at very early stages of the reaction. DLS enables the estimate of the growth of particles in reaction solution, but only before the solution becomes more viscous. Following the relaxation of 1H nuclei in water during RF condensation brings a different view on the system—this technique follows the properties of the present water that is gradually captured in polymeric gel. From this side, the process behaves similarly to the nucleation reaction, which is in contradiction to the n-order mechanism confirmed by other techniques. The widest range of applicability was found for DSC measurement of the freezing/melting behavior of the reaction mixture, which is possible to use without any limitations until full solidification. Furthermore, this approach enables us to follow the gradual formation and development of the gel through the intermediate undergoing glass transition.

Early-age hydration process and autogenous shrinkage evolution of high performance cement pastes

This paper presented a comprehensive study on the early-age hydration process and autogenous shrinkage evolution of high performance cement pastes. The early-age hydration process of cement pastes was analyzed by combining 1H nuclear magnetic resonance relaxometry (1H NMR) with isothermal calorimetry. The hydration degree was contrastively analyzed by using 1H NMR and thermogravimetry analyses (TGA). Moreover, the relationship between the free water consumption process and autogenous shrinkage for cement pastes was revealed. Results showed that a magnetism-heat (M − H) model could be established according to the correspondence between free water consumption rate and hydration exothermic rate, which divided the early-age hydration process of cement pastes into four periods. The initial setting time was the onset that free water signal fraction started to drop, after this moment, the consumption rate of free water was increased and more hydration products were generated. After about final setting time, the weighted mean relaxation time of the free water sharply decreased, and the pore structure of cement pastes was gradually refined. The hydration degree (α) of cement calculated by 1H NMR and TGA showed good agreement, with the error of α values less than 2% after initial setting time. Furthermore, cement paste with a lower water/cement ratio showed higher autogenous shrinkage and lower free water signal fraction, but they did not show a good linear correlation with each other throughout the hydration process.

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.

An Ontology-Based Approach to Enable Data-Driven Research in the Field of NDT in Civil Engineering

Although measurement data from the civil engineering sector are an important basis for scientific analyses in the field of non-destructive testing (NDT), there is still no uniform representation of these data. An analysis of data sets across different test objects or test types is therefore associated with a high manual effort. Ontologies and the semantic web are technologies already used in numerous intelligent systems such as material cyberinfrastructures or research databases. This contribution demonstrates the application of these technologies to the case of the 1H nuclear magnetic resonance relaxometry, which is commonly used to characterize water content and porosity distribution in solids. The methodology implemented for this purpose was developed specifically to be applied to materials science (MS) tests. The aim of this paper is to analyze such a methodology from the perspective of data interoperability using ontologies. Three benefits are expected from this approach to the study of the implementation of interoperability in the NDT domain: First, expanding knowledge of how the intrinsic characteristics of the NDT domain determine the application of semantic technologies. Second, to determine which aspects of such an implementation can be improved and in what ways. Finally, the baselines of future research in the field of data integration for NDT are drawn.

Water dynamics in eggs by means of Nuclear Magnetic Resonance relaxometry

1H Nuclear Magnetic Resonance relaxometry has been applied to reveal dynamical properties of water molecules embedded into egg yolk and white of three species: turkey, chicken and quail. Two fractions of water molecules, referred to as confined-water and free-water fractions, have been revealed. It has been demonstrated that translation diffusion of the confined-water fraction is three-dimensional. The dynamics of the confined-water has been quantitatively described in terms of diffusion coefficients and rotational correlation times. The parameters have been compared for egg yolk and white for all the species. In addition to these quantities, the number of the confined-water molecules per unit volume has been provided for all cases. The obtained parameters provide insight into the dynamics of water in eggs of different origin and allow to identify similarities and differences between them in connection to the structure of the network formed by the macromolecular fraction of egg yolk and white.

Mechanisms dominating thixotropy in limestone calcined clay cement (LC3)

Limestone calcined clay cement (LC3) is a green binder with great practical importance for the cement industry. Growing application has increased the need to understand the mechanisms governing its thixotropy for better control of workability. While formation of C-S-H bridges is understood to dominate the thixotropy of ordinary Portland cement, LC3 paste displayed unique thixotropy properties. In this study, focused beam reflectance measurement, zeta potential, 1H nuclear magnetic resonance relaxometry and micro X-ray computed tomography were used to track the colloidal interaction and hydration extent within LC3 paste. Results showed that flocculation due to the negative surface charge and water affinity of calcined clay appears to be the dominating factor. This leads to a reduction of water available to contribute to fluidity of the paste and, in turn, governing the development of thixotropy over time. In addition, the dilution effect due to high clinker substitution diminishes thixotropy growth with time.

On the quantification of solid phases in hydrated cement paste by 1H nuclear magnetic resonance relaxometry

Different solid phases, important to cement paste hydration, are investigated with low-field benchtop 1H nuclear magnetic resonance (NMR). A combination of the well-established quadrature echo pulse sequence with variable pulse gap together with a T1 saturation recovery quadrature echo pulse sequence is used. The results illustrate the diversity in the 1H NMR relaxation behaviour of solid phases that prospects the differentiation in more complex materials. We propose a procedure to obtain quantified values of the solid compounds using these unique relaxation responses of solids, called finger print, and apply this technique to well-hydrated white and ordinary Portland cement paste. Based on the results, needs and ways for future improvements are discussed.