Spin-lattice Relaxation Time Measurements Research Articles

The use of relaxometry to evaluate the aging process in hybrid HIPS nanocomposites

Nuclear magnetic resonance allows measurement of proton spin-lattice relaxation times, which reflect the molecular mobility of the sample according to the changes in its chemical structure caused by different mechanisms that can be induced. Nanomaterials and their derivatives are good systems to investigate through NMR relaxometry due to their particular organization and intermolecular interaction. In this study, NMR relaxometry was employed to evaluate UV aging of HIPS nanomaterials formed by the solution method. The results obtained were quite interesting. Regardless of organoclay amount, the aging effect occurred slowly up to 200 h of UV light exposure. However, at 300 h of UV light exposure, competition between chain degradation and chain recombination occurred, and at 400 h the aging effect increased the chain scission.

Solid-state 1H and 31P NMR and FTIR spectroscopy study of static and dynamic structures in sol-gel derived calcium hydroxyapatites

Calcium hydroxyapatite containing amorphous phosphate phase (ACP-CaHA) and nano-structured hydroxyapatite (CaHA) have been prepared by two sol-gel synthesis routes. The structural organization of hydroxyl groups in both materials has been determined by means of 1H MAS NMR and FTIR spectroscopy. It has been shown that the amount of structural –OH groups in nano-structured CaHA is significantly higher than that from adsorbed water and vice versa in ACP-CaHA. A precise signal shape analysis has been carried out for both studied samples. The 31P NMR signals have been found being Voigt-shaped in the wide-line as well as in MAS spectra. The 1H and 31P spin-lattice and spin-spin relaxation time measurements have revealed that the fast spin motion takes place in ACP-CaHA. The corresponding correlation time τ ~ 7 · 10–7 s at ~300 K has been determined. The effect of MAS rate on the 31P signal shape also confirms that this motion runs in the time scale of microseconds or even nanoseconds. The magnitude of the anisotropic broadening 1220 ± 20 Hz determined for nano-structured CaHA is very close to the maximum of the dipolar 1H–31P coupling distribution profile estimated using CP MAS kinetics. The dynamics of 1H–31P spin interactions in nano-structured CaHA (τ ~ 3.3 · 10–5 s) is much slower than in ACP-CaHA.

1H nuclear magnetic resonance study of hydrated water dynamics in perfluorosulfonic acid ionomer Nafion

We have studied the dynamics of hydrated water molecules in the proton exchange membrane of Nafion by means of high-resolution 1H nuclear magnetic resonance (NMR) measurements. “Bound” and “free” states of hydrated water clusters as well as the exchange protons were identified from the NMR chemical shift measurements, and their activation energies were obtained from the temperature-dependent laboratory- and rotating-frame spin-lattice relaxation measurements. Besides, a peculiar motional transition in the ultralow frequency region was observed at 373 K for the “free” hydrated water from the rotating-frame NMR spin-lattice relaxation time measurements.

Structural Assignment of Side Chain Liquid Crystalline Monomer and Polymer by 1-D and 2-D Solution NMR Studies

In the present study, the synthesis and characterization of a methacrylic-based side chain liquid crystalline monomer and its polymer were investigated with the aid of both 1-D and 2-D nuclear magnetic resonance (NMR) techniques. The mesophase characteristics of the monomer and polymer were determined by hot-stage optical polarized microscopy (HOPM). The nematic and smectic phases were observed for the monomer and polymer. Furthermore, 13C spin-lattice relaxation time measurements were performed on the above systems in order to monitor molecular dynamics. The present study provides an opportunity to carry out a systematic comparison of the evolution of structural as well as dynamical changes of the monomer and the polymer.

Ionic Pathways in Li13Si4 investigated by 6Li and 7Li solid state NMR experiments

Local environments and dynamics of lithium ions in the binary lithium silicide Li13Si4 have been studied by 6Li MAS-NMR, 7Li spin-lattice relaxation time and site-resolved 7Li 2D exchange NMR measurements as a function of mixing time. Variable temperature experiments result in distinct differences in activation energies characterizing the transfer rates between the different lithium sites. Based on this information, a comprehensive picture of the preferred ionic transfer pathways in this silicide has been developed. With respect to local mobility, the results of the present study suggests the ordering Li6/Li7>Li5>Li1>Li4 >Li2/Li3. Mobility within the z=0.5 plane is distinctly higher than within the z=0 plane, and the ionic transfer between the planes is most facile via Li1/Li5 exchange. The lithium ionic mobility can be rationalized on the basis of the type of the coordinating silicide anions and the lithium-lithium distances within the structure. Lithium ions strongly interacting with the isolated Si4− anions have distinctly lower mobility than those the coordination of which is dominated by Si26− dumbbells.

Fast cation dynamics in the crystalline state of an imidazolium-based room temperature ionic liquid due to the presence of a tiny amount of H2O

We report the results of a 1H NMR spectroscopic study of cation dynamics in the RTIL, 1-butyl-3-methylimidazolium bromide, in its crystalline state with two different but considerably low water contents, 30 ppm and 200 ppm. The results indicate the presence of a minor liquid-like (or solution) component in the crystalline state in samples with the higher water contents. The relative fraction of this “liquid-like” phase in the crystal is estimated to be ca. 1% around room temperature and increases with increasing temperature up to the melting (liquidus) point, the behavior of which is well explained in terms of a two component phase diagram. It is also indicated based on the lever rule that H2O molecules exist at substantially high concentration in the liquid-like phase compared to in the supercooled liquid state, which can significantly change both microscopic and macroscopic properties of the RTIL. 1H NMR spectral line width and spin–lattice relaxation time measurements indicate that the cations in the liquid-like phase are characterized by a rotational dynamics that is distinct from that of the supercooled liquid state with significantly higher mobility. Such high cation mobility results from the interaction between the cations and H2O molecules in the liquid-like phase that reduces the Coulombic interaction between the cations and anions and decreases local viscosity.

Simultaneous measurement of very small magnetic fields and spin-lattice relaxation

A field cycling (FC) NMR experiment is presented which allows for the simultaneous determination of very small magnetic fields down to about 3μT and the concomitant measurement of nuclear spin-lattice relaxation times in these fields. The technique will enable broadband spin-lattice relaxation dispersion experiments down to about 100Hz 1H Larmor frequency. Limitations of its applicability are discussed.

Quantitative Spectroscopic Study of Equilibrium in CO2-Loaded Aqueous 2-(Ethylamino)ethanol Solutions

The chemical absorption of CO2 in aqueous solutions of 2-(ethylamino)ethanol at 313 K was investigated by nuclear magnetic resonance (NMR) spectroscopy. Accurate 13C NMR quantitation by inverse-gated decoupling was achieved on the basis of 13C spin–lattice relaxation time measurements for all species in the system. The concentration of carbonate species (HCO3–/CO32–) monotonically increased with increasing CO2 loading, whereas that of carbamate anion [CH3CH2N(CH2CH2OH)COO–] showed a peak around 0.5 mol of CO2/mol of amine. Furthermore, we found that alkyl carbonate species (CH3CH2NHCH2CH2OCOO–) formed in the high-CO2 loading range, which was confirmed by 2D NMR spectroscopy and density functional theory calculations with a dielectric continuum solvation model at the B3LYP/aug-cc-pVDZ//B3LYP/6-311++G(d,p) level.

The effect of furazolidone on the physico-chemical properties of dimyristoylphosphatidylcholine bilayers: Relevance to anti-leishmanial therapy

In this study, the influence of furazolidone, an anti-leishmanial drug, on dimyristoylphosphatidylcholine (DMPC) liposome hydration degree, mobility and thermodynamics was investigated by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). FTIR results showed that furazolidone was responsible for an increase in the hydrogen bound number and mobility of the lipid phosphate group. Furazolidone also affected the lipid choline group by increasing its motional freedom, as shown by FTIR and 1H NMR spin–lattice relaxation time measurements. At the DMPC interfacial region, FTIR results showed a drug-induced reduction of the carbonyl hydration and order degrees. Very weak interaction among furazolidone and the hydrophobic lipid chains was also observed. However, no furazolidone-induced changes on thermodynamical parameters, such as phase transition temperature (Tm) and enthalpy variation (ΔH), were detected by the DSC technique. Thus, furazolidone seems to interact preferentially with lipid polar and interfacial regions, enhancing the freedom for gauche-trans isomerization of the first methylene groups of DMPC acyl chains. Responses described in this paper may explain the improved activity of furazolidone-encapsulated liposomes by comparison with the effect of the free drug, described in literature. The findings can also improve further strategies for the potential therapeutic application of liposomal furazolidone as a drug delivery system and minimize the risk of drug resistance and collateral effects related to high toxicity.

The spin-lattice relaxation in superfluid inclusions formed in the solid helium matrix

Processes of spin-lattice relaxation in superfluid inclusions, formed during growth and rapid cooling of helium crystals, are studied by the pulse nuclear magnetic resonance method. Measurements of spin-lattice relaxation times were carried out using the two spin-echoes method. This allows to obtain reliable data for each of the coexisting phases of a two-phase system HCP matrix—superfluid inclusions. The samples of the solid solution 1% 3He in 4He with molar volume 20.2 cm3/mol are investigated in the temperature range 1.4–1.9 K. It is found that the time of spin-lattice relaxation in superfluid drops differs significantly from that in bulk superfluid. It is shown that in both cases the dominant relaxation mechanism is the wall relaxation, which is a few orders of magnitude faster than the bulk relaxation. However, in the bulk fluid, the velocity of wall relaxation is determined by the time of diffusion of atoms to the walls, while the spin relaxation processes directly on the wall play a major role in the superfluid inclusions. In the case of superfluid droplets, 3He atoms are the only magnetic impurities on the walls of the inclusions. They are much less efficient magnetic centers than the strong magnetic particles on the walls of the cell. Moreover, a spontaneous dramatic change is observed in the amplitude of one of the echo-signals, which is associated with the solidification of superfluid droplets and the formation of long-lived metastable disordered (glass) state.

13C NMR Study of Superconductivity near Charge Instability Realized in β''-(BEDT-TTF)4[(H3O)Ga(C2O4)3]·C6H5NO2

To investigate the superconducting (SC) state near a charge instability, we performed ^{13}C NMR experiments on the molecular superconductor beta"-(BEDT-TTF)_{4}[(H_{3}O)Ga(C_{2}O_{4})_{3}]C_{6}H_{5}NO_{2}, which exhibits a charge anomaly at 100 K. The Knight shift which we measured in the SC state down to 1.5 K demonstrates that Cooper pairs are in spin-singlet state. Measurements of the nuclear spin-lattice relaxation time reveal strong electron-electron correlations in the normal state. The resistivity increase observed below 10 K indicates that the enhanced fluctuation has an electric origin. We discuss the possibility of charge-fluctuation-induced superconductivity.

Rotating-frame nuclear magnetic resonance study of the superprotonic conduction in LiH2PO4

The proton and phosphorus dynamics of the superprotonic conduction in the LiH2PO4 system has been studied by means of 1H and 31P NMR rotating-frame nuclear magnetic resonance (NMR). The temperature-dependent 1H NMR rotating-frame spin–lattice relaxation time measurements revealed in a sensitive manner the evolution of the microscopic environment and proton dynamics of the two distinct hydrogen-bond types in the system, which is quite compatible with the electrical conductivity and the impedance spectroscopy measurements. Besides, the proton dynamics was found to be coupled to the reorientational motion of the PO4 tetrahedra.

NMR studies of water-gas interactions

The analysis of reported data concerning the solubility of different gases in water depending on a temperature was carried out. These dependences could be described by mono- or biexponential function. Solubilities of nitrogen and oxygen are additive and depend on their percentage in the atmosphere above the fluid. The temperature dependence of oxygen and nitrogen dissolved in water corresponds to that in the atmospheric air. The measurements of water spin-lattice relaxation times changing upon the concentration of dissolved paramagnetic oxygen showed that the oxygen could be significantly but not completely eliminated by saturation with any gases. The best method is the contact with a water immiscible liquid with higher gas capacity than water. However, it results in unstable state of a gas-water system converging to equilibrium.

NMR investigation of the low-temperature dynamics of solid4He doped with3He impurities

The lattice dynamics of solid ${}^{4}$He has been explored using pulsed NMR methods to study the motion of ${}^{3}$He impurities in the temperature range (0.05--0.20 K) where experiments have revealed anomalies attributed to superflow or unexpected viscoelastic properties of the solid ${}^{4}$He lattice. We report the results of measurements of the nuclear spin-lattice and spin-spin relaxation times that measure the fluctuation spectrum at high and low frequencies, respectively, of the ${}^{3}$He motion that results from quantum tunneling in the ${}^{4}$He matrix. The measurements were made for ${}^{3}$He concentrations $16<{x}_{3}<2000$ ppm. For ${}^{3}$He concentrations ${x}_{3}=16$ and 24 ppm, large changes are observed for both the spin-lattice relaxation time ${T}_{1}$ and the spin-spin relaxation time ${T}_{2}$ at temperatures close to those for which the anomalies are observed in measurements of torsional oscillator responses and the shear modulus. These changes in the NMR relaxation rates were not observed for higher ${}^{3}$He concentrations.

Understanding the Conduction Mechanism of the Protonic Conductor CsH2PO4 by Solid-State NMR Spectroscopy

Local dynamics and hydrogen bonding in CsH2PO4 have been investigated by 1H, 2H, and 31P solid-state NMR spectroscopy to help provide a detailed understanding of proton conduction in the paraelectric phase. Two distinct environments are observed by 1H and 2H NMR, and their chemical shifts (1H) and quadrupolar coupling constants (2H) are consistent with one strong and one slightly weaker H-bonding environment. Two different protonic motions are detected by variable-temperature 1H MAS NMR and T1 spin–lattice relaxation time measurements in the paraelectric phase, which we assign to librational and long-range translational motions. An activation energy of 0.70 ± 0.07 eV is extracted for the latter motion; that of the librational motion is much lower. 31P NMR line shapes are measured under MAS and static conditions, and spin–lattice relaxation time measurements have been performed as a function of temperature. Although the 31P line shape is sensitive to the protonic motion, the reorientation of the phosphate ...

Spin-polarized state quantum filter used to measure spin-polarized state relaxation time and g-factor

A novel method for measurement of g-factor and spin-lattice relaxation time of spin-polarized states in nano-layers of different chemical nature was developed. This method is based on usage of spin-polarized state quantum filter, which was created and tested earlier [V. I. Makarov et al., J Appl. Phys. 110, 063717 (2011) and V. I. Makarov et al., J Appl. Phys. 112, 084310 (2012). The spin state parameters were measured in nanolayers of different materials (Fe, Au, and Si) in function of such experimental parameters as the layer thickness and temperature. The phenomenological model developed earlier for steady-state conditions was presently extended to include time dependence and successfully used in the data analysis. Qualitative models were proposed that explain the observed dependences, forming the basis for future theoretical developments.

Dynamic Molecular Behavior and Cluster Structure of Octanoic Acid in Its Liquid and CCl<sub>4</sub> Solution

Fatty acids such as oleic and stearic acids having a long hydrocarbon chain are known to exist as dimers in their melt and even in a non-polar solvent. In their melt the dimers arrange longitudinally and alternately to form clusters which resemble a smectic liquid crystal. The clusters determine the liquid properties of the fatty acids such as density, viscosity and fluidity. Then, do the dimers of fatty acid having a moderate-length hydrocarbon chain construct such the clusters? In the present study the dynamic molecular behavior and assembly structure of octanoic acid in its melt and also in CCl4 solution have been investigated by the X-ray diffraction, near infrared spectroscopy, 1H-NMR chemical shift, self-diffusion coefficient and 13C-NMR spin-lattice relaxation time measurements. From these results it has been revealed that the clusters of octanoic acid exist in its melt and also in CCl4 and that the clusters in the melt disintegrate with an increase in temperature. The dissociation profile of dimers of octanoic acid into monomers in CCl4 also has been clarified.

A Comparative Study of the Rotational Dynamics of PF6– Anions in the Crystals and Liquid States of 1-Butyl-3-methylimidazolium Hexafluorophosphate: Results from 31P NMR Spectroscopy

The rotational dynamics of the hexafluorophosphate anion (PF(6)(-)) in the crystalline and liquid states of the archetypal room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim]PF(6)) are investigated using (31)P NMR spectroscopy line shape analyses and spin-lattice relaxation time measurements. The PF(6)(-) anion performs isotropic rotation in all three polymorphic crystals phases α, β, and γ as well as in the liquid state with a characteristic time scale that ranges from a few ps to a few hundred ps over a temperature range of 180-280 K. The rotational correlation time τ(c) for PF(6)(-) rotation follows the sequence γ-phase < α-phase ≈ liquid < β-phase. On the other hand, in the liquid state, all local motions in the cation as well as its global rotational reorientation are characterized by time scales that are slower compared to that for the PF(6)(-) anion rotation. The time scale τ(c) and the activation energy of PF(6)(-) rotation in this RTIL are found to be comparable with those observed in ordinary alkali and ammonium salts despite the large counterion size and low melting point of the former. The high sphericity of the PF(6)(-) ion is hypothesized to play an important role in the decoupling of its rotational dynamics that appear to be practically independent of the averaged cation-anion interaction.

Nuclear Spin Relaxation of Very Dilute 3He impurities in Solid 4He

We report measurements of the nuclear spin-lattice and spin-spin relaxation times of very dilute 3He in solid 4He in the temperature range 0.01 ≤ T ≤ 0.5 K for densities where anomalies have been observed in torsional oscillator and shear modulus measurements. We compare the results with the values of the relaxation times reported by other observers for higher concentrations and the theory of Landesman that takes into account the elastic properties of the 4He lattice. A sharp increase in the magnitude of the nuclear spin-lattice relaxation times compared to the the classical Landesman theory is observed close to the temperatures where the torsional and shear modulus anomalies are observed. The NMR results suggest that the tunneling of 3He impurities in the atomic-scale elastic distortion is affected by the same processes that give rise to the macroscopic elastic dissipation anomalies.

Nuclear magnetic resonance study on rotational dynamics of water and benzene in a series of ionic liquids: Anion and cation effects

The rotational correlation times (τ(2R)) for polar water (D(2)O) molecule and apolar benzene (C(6)D(6)) molecule were determined in ionic liquids (ILs) by means of the (2)H (D) NMR spin-lattice relaxation time (T(1)) measurements. The solvent IL was systematically varied to elucidate the anion and cation effects separately. Five species, bis(trifluoromethylsulfonyl)imide (TFSI(-)), trifluoromethylsulfonate (TfO(-)), hexafluorophosphate (PF(6)(-)), chloride (Cl(-)), and formate (HCOO(-)), were examined for the anion effect against a fixed cation species of 1-butyl-3-methyl-imidazolium (bmim(+)). Four species, bmim(+), N-methyl-N-butylpyrrolidinium (bmpy(+)), N,N,N-trimethyl-N-propylammonium (N(1,1,1,3)(+)), and P,P,P-trihexyl-P-tetradecylphosphonium (P(6,6,6,14)(+)), were employed for the cation effect against a fixed anion species of TFSI(-). The τ(2R) ratio of water to benzene, expressed as τ(W/B), was used as a probe to characterize the strength of Coulombic solute-solvent interaction in ILs beyond the hydrodynamic limit based on the excluded-volume effect. The τ(W/B) value was found to strongly depend on the anion species, and the solute dynamics are sensitive not only to the size but also to the chemical structure of the component anion. The cation effect was rather weak, in contrast. The largest and most hydrophobic P(6,6,6,14)(+) cation was exceptional and a large τ(W/B) was observed, indicating a unique solvation structure in [P(6,6,6,14)(+)]-based ILs.