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1.
‘Unexpected’ proton spin‐lattice relaxation (T1) times are reported for the solutions of poly(ethylene‐co‐1‐octene) and tetrachloroethane‐d2. For the residual protons of the deuterated solvent and the methyl and vinyl protons at the polymer chain ends, their T1 relaxation times vary significantly with both the polymer concentration and molecular weight over a wide range. The T1s also decrease with increasing temperature at relative high temperatures. Such behaviors are in contrast to most reported polymer solutions in which the T1 has nearly no concentration or molecular weight dependence in the dilute and semi‐dilute regime, and normal dependence on temperature. Further investigation revealed that the paramagnetic oxygen effect did shorten the measured proton T1s, but cannot account for the unexpected T1 dependences. Spin rotation is proposed to provide a reasonable explanation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
2.
《Physics and Chemistry of Liquids》2012,50(4):219-224
Abstract The proton magnetic resonance (PMR) spin-lattice and spin-spin relaxation times (T1 and T2) were measured in aqueous solutions of glycine and L-proline as a function of solute concentrations and at a temperature of 32°C. The relaxation times were measured using Bruker PC 120 NMR process analyser. The relaxation times were found to decrease with increase of solute concentrations. The results are interpreted on the basis of flickering cluster model and hydrogen bond formation between solute and solvent molecules. 相似文献
3.
M. Forsyth M. E. Smith P. Meakin D. R. MacFarlane 《Journal of Polymer Science.Polymer Physics》1994,32(12):2077-2084
Sodium triflate/polyether urethane polymer electrolytes ranging in concentration from 0.05 molal to 1.75 molal have been investigated via 23Na static solid-state NMR. Room temperature spectra and spin lattice relaxation times were consistent with a single narrow resonance indicating the presence of only mobile ionic species. The concentration and temperature dependence of relaxation times, chemical shifts, and linewidth have been investigated. The results suggest either a single species or rapid exchange between a number of species (even at temperatures below the glass transition temperature, Tg). The linewidth decreases with increasing concentration of ions and remains temperature independent below Tg. Below Tg a maximum quadrupolar interaction constant of 2 MHz is calculated. The addition of plasticizer to the polymer electrolyte causes significant chemical shift changes that depend on the solvent donicity of the plasticizer. The linewidth and T1 relaxation times also depend on the Tg of the plasticized systems. Previous 23Na NMR literature results are reviewed and qualitative models developed to account for the variation in results. © 1994 John Wiley & Sons, Inc. 相似文献
4.
Summary Quantitative determination of the concentration of paramagnetic ions in aqueous solutions is performed by NMR relaxation titration. By measurement of the nuclear spin-lattice relaxation time T
1 or the nuclear spin-spin relaxation time T2 redox titrations and complexometric determinations of the concentration of paramagnetic ions are possible. Also the precipitation of ions from the solution can be followed by this method. The use of a magnetic indicator in this analytical method is shown. The sensitivity of the method goes down to concentrations as low as 10–3 M. The accuracy of NMR relaxation titration is better than 1%. A number of applications of the method are given.
Kernmagnetische Relaxationstitration
Zusammenfassung Quantitative Bestimmungen von paramagnetischen Ionen in wäßrigen Lösungen können mit Hilfe der kernmagnetischen Relaxationstitration durchgeführt werden. Durch Messung der Kernspin-Gitter-Relaxationszeit T 1 oder der Kernspin-Kernspin-Relaxationszeit T 2 als Funktion der Ionenkonzentration sind Redoxtitrationen oder komplexometrische Titrationen möglich. Der quantitative Ablauf von Fällungen kann ebenfalls verfolgt werden. Die Verwendung von magnetischen Indicatoren bei der Relaxationstitration wird beschrieben. Bestimmungen von Ionenkonzentrationen bis herab zu 10–3 M Lösungen sind z.Z. möglich. Die Methode erlaubt eine Genauigkeit der Konzentrationsbestimmung von 1% und besser. Die Anwendung der Methode wird an einer Reihe von Beispielen gezeigt.相似文献
5.
6.
Masahiro Kikuchi Hiromi Kameya Yuhei Shimoyama Mitsuko Ukai Yasuhiko Kobayashi 《Radiation Physics and Chemistry》2012,81(10):1639-1645
We measured the relaxation times of radicals in saccharides upon γ-irradiation by means of X-band pulsed electron paramagnetic resonance (EPR) spectroscopy. We found that the field-swept signal of irradiated fructose by pulsed EPR showed three to four peaks depending on the dose. The relaxation times (T1 and T2) of the side peaks were longer than those of the main peak(s) from each irradiation, indicating that the radicals showing side peaks interact less with the surrounding environment. From relaxation time measurements of several irradiated saccharides, we conclude that T2 relaxation times decrease with the increasing irradiation dose. In contrast, T1 relaxation times show no correlation with the irradiation dose. 相似文献
7.
《Comptes Rendus de l''Academie des Sciences Series IIB Mechanics Physics Astronomy》2001,4(11):825-832
The principles of the intermolecular relaxation of a nuclear spin by its fluctuating magnetic dipolar interactions with the electronic spins of the paramagnetic surrounding species in solution are briefly recalled. It is shown that a very high dynamic nuclear polarization (DNP) of solvent protons is obtained by saturating allowed transitions of free radicals with a hyperfine structure, and that this effect can be used in efficient Earth field magnetometers. Recent work on trivalent lanthanide Ln3+ aqua complexes in heavy water solutions is discussed, including paramagnetic shift and relaxation rate measurements of the 1H NMR lines of probe solutes. This allows a determination of the effective electronic magnetic moments of the various Ln3+ ions in these complexes, and an estimation of their longitudinal and transverse electronic relaxation times T1e and T2e. Particular attention is given to Gd(III) hydrated chelates which can serve as contrast agents in magnetic resonance imaging (MRI). The full experimental electronic paramagnetic resonance (EPR) spectra of these complexes can be interpreted within the Redfield relaxation theory. Monte-Carlo simulations are used to explore situations beyond the validity of the Redfield approximation. For each Gd(III) complex, the EPR study leads to an accurate prediction of T1e, which can be also derived from an independent relaxation dispersion study of the protons of the probe solutes. 相似文献
8.
M. Paczwa A. A. Sapiga M. Olszewski N. A. Sergeev A. V. Sapiga 《Journal of Structural Chemistry》2016,57(2):319-324
The mobility of water molecules in natural natrolite (Na2Al2Si3O10?2H2O) is investigated by the 1H NMR method. The spin-lattice relaxation times in the laboratory and rotating frames (T1 and T1ρ) are measured as a function of the temperature for a polycrystalline sample. From experimental T1 data it follows that at T > 286 K the diffusion of water molecules along channels parallel to the c axis is observed. From experimental T1ρ data it follows that at T > 250 K the diffusion of water molecules in transversal channels of natrolite is also observed. At a low temperature (T < 250 K) the dipolar interaction with paramagnetic impurities (presumably Fe3+ ions) becomes significant as a relaxation mechanism of 1H nuclei. 相似文献
9.
Eiji Hashimoto Yuichi Seshimo Keita Sasanuma Yuichiro Aoki Hitoshi Kanazawa Yuji Ike Seiji Kojima 《Journal of Thermal Analysis and Calorimetry》2010,99(1):45-50
The fragility of ethylene glycol and glucose aqueous solution systems has been investigated by temperature-modulated differential
scanning calorimetry (TMDSC). The frequency and temperature dependences of complex specific heat have been observed in the
vicinity of a glass-transition temperature T
g
. It is shown that the value of the fragility index m can be determined from the temperature dependence of the α-relaxation times observed by TMDSC. We have also studied the elastic
properties of these aqueous solutions by micro-Brillouin scattering, and determined these relaxation times of elastic properties
in the gigahertz range. 相似文献
10.
Abstract Simple formulae which yield a close approximation to the exact analytic solution for the longitudinal and transverse relaxation times T || and T ⊥ of the components of the dipole moment of a nematic liquid crystal with simple uniaxial anisotropy are presented. The new formula for T || yields a substantial correction to the Meier-Saupe formula [1966, Molec. Crystals, 1, 515]. It appears that both the longitudinal and transverse relaxation processes may be accurately described by a single Debye type relaxation mechanism with relaxation times T || and T ⊥. 相似文献
11.
Spin-lattice 1H and 13C nuclear magnetic relaxation (NMR) times T1 have been measured for solutions of polystyrene in hexachlorobutadiene at two different frequencies. Some nuclear Overhauser enhancements and linewidths have also been determined. At 15 and 25 MHz the relaxation times T1 of the ortho and meta carbons show two different dependences on temperature. These measurements indicate internal motion of phenyl groups around the Cα—Cpara axis. A single isotropic correlation time is inadequate to explain the relaxation data for the para carbon. Use of a diamond-lattice motional model reveals that segmental reorientation of the chain backbone of polystyrene can be described in terms of two correlation times, ρ characterizing the three-bond motion process, and θ reflecting either isotropic motions of subchains or departure from an ideal lattice. Data on low-molecular-weight polystyrene indicate the participation of overall rotatory diffusion in the relaxation process. This motion is no longer efficient in high-molecular-weight polymers, where relaxation is due to segmental reorientation. 相似文献
12.
Masayoshi Ito Tetsuo Kanamoto Koji Tanaka Roger S. Porter 《Journal of Polymer Science.Polymer Physics》1985,23(1):59-71
Proton spin–spin relaxation times and the Weibull coefficient have been measured as functions of temperature for poly(ethylene terephthalate) (PET) drawn at 50°C in both the amorphous and the semicrystalline (50%) states. Two relaxation times T2a (long) and T2c (short) are observed for all samples. They are ascribed, respectively, to the relaxation of the amorphous and of the crystalline components including highly strained noncrystalline segments. Effects of initial morphology are found for chain mobility in the noncrystalline regions and for the crystal perfection, evaluated from T2a and the Weibull coefficient μc of the T2c-component, respectively. For all draw ratios, T2a for extrudates prepared from the semicrystalline polymer (C-50) is short compared to that for preparations from the amorphous (A-50) polymer. In the A-50 samples, the perfection of stress-induced crystals increase with increasing draw ratio. In the C-50 samples, the crystal orientation increases, whereas the perfection decreases with increasing draw ratio. To improve the crystal perfection, annealing at higher temperature or longer time is required for C-50 as compared with A-50. The value of μc correlates well with the change in crystal perfection during deformation and annealing. 相似文献
13.
Electron spin relaxation times and rapid scan EPR imaging of pH‐sensitive amino‐substituted trityl radicals
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Hanan B. Elajaili Joshua R. Biller Mark Tseitlin Ilirian Dhimitruka Valery V. Khramtsov Sandra S. Eaton Gareth R. Eaton 《Magnetic resonance in chemistry : MRC》2015,53(4):280-284
Carboxy‐substituted trityl (triarylmethyl) radicals are valuable in vivo probes because of their stability, narrow lines, and sensitivity of their spectroscopic properties to oxygen. Amino‐substituted trityl radicals have the potential to monitor pH in vivo, and the suitability for this application depends on spectral properties. Electron spin relaxation times T1 and T2 were measured at X‐band for the protonated and deprotonated forms of two amino‐substituted triarylmethyl radicals. Comparison with relaxation times for carboxy‐substituted triarylmethyl radicals shows that T1 exhibits little dependence on protonation or the nature of the substituent, which makes it useful for measuring O2 concentration, independent of pH. Insensitivity of T1 to changes in substituents is consistent with the assignment of the dominant contribution to spin lattice relaxation as a local mode that involves primarily atoms in the carbon and sulfur core. Values of T2 vary substantially with pH and the nature of the aryl group substituent, reflecting a range of dynamic processes. The narrow spectral widths for the amino‐substituted triarylmethyl radicals facilitate spectral‐spatial rapid scan electron paramagnetic resonance imaging, which was demonstrated with a phantom. The dependence of hyperfine splittings patterns on pH is revealed in spectral slices through the image. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
14.
The environmental relaxation model was applied successfully to explain the temperature dependence of viscosity, conductance, and the Walden product of molten Ca(NO3)2.3.91H2O + NiCl2 system in the non-Arrhenius region. This model was applied to pure melts, binary molten salt systems with ideal solutions marked by the absence of complex ions, and systems in which octahedral or tetrahedral complexes are formed. The values of the glass transition temperature obtained from the free volume and environmental relaxation models are in good agreement. The values of apparent activation energies for viscous and conductance flows derived from these two models are also comparable. 相似文献
15.
The dynamic-structural changes and polymer - solvent interactions during the thermotropic phase transition in poly(vinyl methyl ether) (PVME)/D2O solutions in a broad range of polymer concentrations (c = 0.1-60 wt.-%) were studied combining the measurements of 1H NMR spectra, spin-spin (T2) and spin-lattice (T1) relaxation times. Phase separation in solutions results in a marked line broadening of a major part of polymer segments, evidently due to the formation of compact globular-like structures. The minority (∼15%) mobile component, which does not participate in the phase separation, consists of low-molecular-weight fractions of PVME, as shown by GPC. Measurements of spin-spin relaxation times T2 of PVME methylene protons have shown that globular structures are more compact in dilute solutions in comparison with semidilute solutions where globules probably contain a certain amount of water. A certain portion of water molecules bound at elevated temperatures to (in) PVME globular structures in semidilute and concentrated solutions was revealed from measurements of spin-spin and spin-lattice relaxation times of residual HDO molecules. 相似文献
16.
G. A. Samara 《Journal of Polymer Science.Polymer Physics》1992,30(7):669-679
The effects of hydrostatic pressure to 20 kbar on the β molecular relaxation process of polyvinylidene fluoride (PVDF) and on the dielectric properties in the neighborhood of this relaxation have been investigated. This relaxation has a strong influence on the electrical and mechanical properties of PVDF. Pressure causes a large shift to higher temperatures (~ 10K/kbar) of the dielectric relaxation peak and a decrease in the width of the distribution of relaxation times. This slowing down of the relaxation process is discussed in terms of the Vogel–Fulcher equation and related models, and it results from an increase in both the energy barrier to dipolar motion and the reference temperature (T0) for the kinetic relaxation process which represents the “static” dipolar freezing temperature for the process. The general applicability of the Vogel–Fulcher equation to relaxional processes in polymers and other systems is briefly discussed. The pressure dependence of the dielectric constant both above and below the relaxation peak temperature (Tmax) is found to be dominated by the change in polarizability. The effect is larger above Tmax because of the relatively large decrease in the dipolar orientational polarizability with pressure. 相似文献
17.
Frans A. A. Mulder Leonardo Tenori Claudio Luchinat 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(43):15427-15430
NMR spectroscopy is an indispensable technique for the determination of the chemical identity and structure of small molecules. The method is especially recognized for its robustness and intrinsically quantitative nature, and has manifested itself as a key analytical platform for diverse fields of application, ranging from chemical synthesis to metabolomics. Unfortunately, the slow recovery of nuclear spin polarization by spin‐lattice (T1) relaxation causes most experimental time to be lost on idle waiting. Furthermore, truly quantitative NMR (qNMR) spectroscopy requires waiting times of 5‐times the longest T1 in the sample, making qNMR spectroscopy slow and inefficient. We demonstrate here that co‐solute paramagnetic relaxation can mitigate these two problems simultaneously. The addition of a small amount of paramagnetic gadolinium chelate, available in the form of commercial contrast‐agent solutions, enables cheap, quantitative, and efficient high‐throughput mixture analysis. 相似文献
18.
A. Agrawal 《Journal of Polymer Science.Polymer Physics》1989,27(7):1449-1461
Isothermal enthalpy relaxation in polystyrene was measured as a function of temperature and molecular weight on a differential scanning calorimeter. Relaxation spectra were derived from the data and expressed as a distribution of relaxation times. For a given molecular weight the relaxation spectra at different temperatures could not be superimposed by a shift in time. The relaxation curves of samples of different molecular weights could be superimposed only when the difference between the temperature at which the relaxation was monitored (Ta) and their respective Tg was the same. The relaxation spectrum at any temperature for a given molecular weight was also expressed as a distribution of energies. The average energy represented by this distribution was associated with an activation energy required for the motion of a chemical repeat unit. The activation energy extracted from the temperature shift in the relaxation spectra corresponded to the motion of a statistical unit (Kuhn's segment) in polystyrene. 相似文献
19.
D. Barkowski W. Mersch Th. Dorfmüller 《Journal of Polymer Science.Polymer Physics》1982,20(6):953-959
The reorientational relaxation of 9-cyananthracene fluorescent label molecules has been measured in bulk polybutadiene and solutions with cyclohexane by a fluorescent depolarization technique. The procedure adopted consists in the incorporation of an Arrhenius temperature dependence of the orientational relaxation time in the Perrin equation, thus obviating the necessity of an independent determination of the intrinsic polarization ratio P0 and enabling one to obtain the preexponential factors and the activation energies of the reorientational relaxation times. The most noteworthy result in our view is the validity of the Arrhenius equation for the effective microviscosity as opposed to the validity of the Fulcher–Vogel–Tamann equation with a glass point of T0 = 136 K for the shear viscosity of a polymer solution (90%). 相似文献
20.
Translational diffusion of tetracene and rubrene in bisphenol A polysulfone (Tg = 460 K) was measured using a holographic fluorescence recovery after photobleaching (FRAP) technique. In the temperature range from 493 to 462 K, probe translation was diffusive and the translational diffusion coefficients varied from 10−8 to 10−13 cm2/s. Surprisingly, the observed translational diffusion coefficients showed a weaker temperature dependence than the rotational correlation times of the same probes. Rotational correlation times have the same temperature dependence as the viscoelastic relaxation times characteristic of the rubberlike modulus, while translational relaxation times decouple from the viscoelastic relaxation times. On average, probe molecules are translating larger and larger distances per probe rotation time as the temperature is lowered to Tg. These results can be explained qualitatively in terms of spatially heterogeneous segmental dynamics in the polysulfone matrix. © 1996 John Wiley & Sons, Inc. 相似文献