Study of molecular motion in drawn polyethylene by broad-line nuclear magnetic resonance

Measurements have been made of the anisotropy in the nuclear magnetic resonance second moment for the proton resonance in drawn low density polyethylene films over the temperature range –196 to +60° C.The experimental results are first compared with the theoretical predictions of a model in which it is assumed that the polyethylene chains undergo coherent classical rotation about the chain axis. This model is successful in predicting the general pattern of anisotropy at temperatures close to the melting point.To account for the observed reduction in second moment at intermediate temperatures further calculations are described, based on a model in which the polyethylene chains twist about the chain axis, the total twist being shared equally between all monomer units. This does not account satisfactorily for the changes in second moment with temperature.It is concluded that satisfactory general agreement between theory and experiment is reached if the measured anisotropy at intermediate temperatures derives from rigid lattice intramolecular interactions only, and that the intermolecular interactions are averaged to a small value. It is suggested that the inter-chain averaging occurs by a chain-sliding process.At higher temperatures further reduction in the second moment occurs due to coherent chain oscillation about the chain axis, which finally leads to complete rotation at premelting point temperatures.     

Characterization of absorbed water in aramid fibre by nuclear magnetic resonance

While many studies have focused on the mechanical degradation of aramid/epoxy composites by water absorption, little work has been done to gain a deeper understanding of the interaction between absorbed water and aramid fibres. In this study, ¹³C, ¹H, and ²³Na nuclear magnetic resonance was used to show that the absorbed water in Twaron fibre is located in small pores in the skin region of the fibres, and in larger core defects. The absorbed water partially dissolves sodium salts, consisting mainly of sodium carbonate, which are present in the pores. No evidence of chemical breakdown of the aramid polymer, or of water ingress within the polymer lattice, was observed.     

Determination of the average size and concentration of air bubbles in water by nuclear magnetic resonance

Nuclear magnetic resonance has been used to determine the mean radius of air bubbles in distilled water that has stood for a long time and the volume concentration of these “reduced to mean radius” bubbles. It is shown that the kinetics of the change in the concentration of these bubbles can be observed from the change in the spin-spin relaxation time. Pis’ma Zh. Tekh. Fiz. 23, 42–45 (July 12, 1997)     

Structure of dispersion media by nuclear magnetic resonance

The change of the diamagnetic shielding constant of a benzene molecule interacting with the solid phase surface is calculated.Notation _d diamagnetic shielding constant - e, m_e electron charge and mass, respectively - c speed of light - _b ^o benzene wave function - _m ^o and _m ^o* eigenfunctions of benzene molecule and their conjugates - W_mo matrix elements of the perturbation operator - E _o ^o energy of the ground state of a benzene molecule - e _m ^o energy of the excited states of a benzene molecule - a ₀ Bohr radius Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 476–482, September, 1981.     

The photomagnetic effect detected by nuclear magnetic resonance

The results of experiments with transparent easy-plane antiferromagnetic iron borate (FeBO₃) show that nuclear magnetic resonance (NMR) offers an effective tool for the study of photomagnetism in magnetically ordered materials. It is established that illumination of a FeBO₃ sample leads to a shift of the ⁵⁷Fe NMR frequency due to a change in the electron magnetization and significantly increases the nuclear induction signal intensity in the range of existence of the domain boundaries.     

On the quantumness of correlations in nuclear magnetic resonance

Nuclear magnetic resonance (NMR) was successfully employed to test several protocols and ideas in quantum information science. In most of these implementations, the existence of entanglement was ruled out. This fact introduced concerns and questions about the quantum nature of such bench tests. In this paper, we address some issues related to the non-classical aspects of NMR systems. We discuss some experiments where the quantum aspects of this system are supported by quantum correlations of separable states. Such quantumness, beyond the entanglement-separability paradigm, is revealed via a departure between the quantum and the classical versions of information theory. In this scenario, the concept of quantum discord seems to play an important role. We also present an experimental implementation of an analogue of the single-photon Mach-Zehnder interferometer employing two nuclear spins to encode the interferometric paths. This experiment illustrates how non-classical correlations of separable states may be used to simulate quantum dynamics. The results obtained are completely equivalent to the optical scenario, where entanglement (between two field modes) may be present.     

Thermometric detection of nuclear magnetic resonance

Nuclear magnetic resonance has been detected in nonmagnetic materials by observing the temperature rise in the sample. The experiments were performed at temperatures between 1 and 4 K, and results are presented for the²⁷Al resonance in aluminum metal and the¹⁹F resonance in a sample of doped CaF₂. The primary sources of noise have been identified and ways of improving the apparatus are discussed. The technique could prove useful in experiments that require a large range of frequencies to be swept and in experiments investigating the effects of strong rf fields.     

Quantum information processing by nuclear magnetic resonance on quadrupolar nuclei

Nuclear magnetic resonance is viewed as an important technique for the implementation of many quantum information algorithms and protocols. Although the most straightforward approach is to use the two-level system composed of spin 1/2 nuclei as qubits, quadrupolar nuclei, which possess a spin greater than 1/2, are being used as an alternative. In this study, we show some unique features of quadrupolar systems for quantum information processing, with an emphasis on the ability to execute efficient quantum state tomography (QST) using only global rotations of the spin system, whose performance is shown in detail. By preparing suitable states and implementing logical operations by numerically optimized pulses together with the QST method, we follow the stepwise execution of Grover's algorithm. We also review some work in the literature concerning the relaxation of pseudo-pure states in spin 3/2 systems as well as its modelling in both the Redfield and Kraus formalisms. These data are used to discuss differences in the behaviour of the quantum correlations observed for two-qubit systems implemented by spin 1/2 and quadrupolar spin 3/2 systems, also presented in the literature. The possibilities and advantages of using nuclear quadrupole resonance experiments for quantum information processing are also discussed.     

Measurement of ionic diffusion in lithium fluoride by nuclear magnetic resonance techniques

Rates of diffusion of ⁷Li and ¹⁹F were investigated in doped crystals of lithium fluoride using the technique of motional narrowing of nuclear magnetic resonance lines. Major doping elements were divalent Mg and Mn ions, present in amounts between 3 and 240 × 10^–6 cation site fraction. Extrinsic vacancies introduced by this doping increased Li ion diffusion and caused ⁷Li motional narrowing to begin at lower temperatures for greater impurity contents.Diffusivities were determined from the motional narrowing curves using a method of analysis which reduces uncertainties due to magnetic field inhomogeneity and other temperature independent contributions to line broadening. Resulting log D vs 1/T plots showed the expected intrinsic, free vacancy extrinsic, and divalent ion-vacancy association regions of Li ion diffusivity. Activation energies determined for these regions were 1.87±0.09, 0.66±0.03, and 0.91±0.05 eV, respectively. These values yielded the energy for motion of a cation vacancy as 0.66 eV and the energy of formation of a Schottky defect as 2.42 eV.Experimental results obtained earlier in powdered LiF: Mn samples are clarified, and indications concerning the effects of other impurities on Li ion diffusion are presented and discussed.     

11B nuclear magnetic resonance in boron-doped diamond

Abstract

This review summarizes recent results obtained by ¹¹B solid-state nuclear magnetic resonance (NMR) on boron-doped diamond, grown by the high-pressure high-temperature (HPHT) or chemical vapor deposition techniques. Simple single-pulse experiments as well as advanced two-dimensional NMR experiments were applied to the boron sites in diamond. It is shown that magic-angle spinning at magnetic fields above 10 T is suitable for observation of high-resolution ¹¹B spectra of boron-doped diamond. For boron-doped HPHT diamonds, the existence of the excess boron that does not contribute to electrical conductivity was confirmed and its ¹¹B NMR signal was characterized. The point-defect structures (B+H complexes and -B-B-/-B-C-B- clusters), postulated previously for the excess boron, were discarded and graphite-like structures were assigned instead.     

11B nuclear magnetic resonance in boron-doped diamond

This review summarizes recent results obtained by ¹¹B solid-state nuclear magnetic resonance (NMR) on boron-doped diamond, grown by the high-pressure high-temperature (HPHT) or chemical vapor deposition techniques. Simple single-pulse experiments as well as advanced two-dimensional NMR experiments were applied to the boron sites in diamond. It is shown that magic-angle spinning at magnetic fields above 10 T is suitable for observation of high-resolution ¹¹B spectra of boron-doped diamond. For boron-doped HPHT diamonds, the existence of the excess boron that does not contribute to electrical conductivity was confirmed and its ¹¹B NMR signal was characterized. The point-defect structures (B+H complexes and -B-B-/-B-C-B- clusters), postulated previously for the excess boron, were discarded and graphite-like structures were assigned instead.     

Microinhomogeneity of high-alkali aluminosilicate glasses studied by nuclear magnetic resonance spectroscopy

The structure of quenched aluminosilicate glasses with Na₂O/Al₂O₃ > 1 has been studied by high-resolution nuclear magnetic resonance spectroscopy. The aluminum in the structure of the glasses is shown to be in fourfold coordination. Increasing the sodium oxide content of the glasses reduces the degree of polymerization in their structure and leads to a nonuniform nonbridging oxygen distribution over the aluminosilicate glass network. The glasses have a locally microinhomogeneous structure due to the presence of both highly polymerized aluminosilicate anion groups and relatively depolymerized silicate anions.     

Characterization of hydrogenated amorphous carbon films by nuclear magnetic resonance techniques

Different nuclear magnetic resonance (NMR) methods have been used to investigate the structure of hydrogenated amorphous carbon films. Besides measuring the sp²-to-sp³ ratio by means of ¹³C cross-polarization magic-angle spinning total suppression of spinning sidebands NMR we studied the distribution of covalently bound hydrogen over sp²- and sp³-type carbon atoms using dipolar dephasing techniques. The reliability of the dipolar dephasing measurements is discussed and the results are compared with the data derived from a simple statistical model. Moreover they are compared with previous IR spectroscopy measurements. ¹H combined rotation-and-multipulse NMR spectra are presented which do not show resolved proton resonances in the case of as-deposited films but correspond in their line shape to the proton distribution measured with dipolar dephasing. Finally a few considerations concerning a refined structural model are presented.     

Study of the porous structure of hardened gypsum by pulsed nuclear magnetic resonance

The porous structure of hardened gypsum prepared by hydration of CaSO₄·0.5H₂O and CaSO₄ was studied by nuclear magnetic resonance. The combined analysis of the melting curves of water confined in pores, the shapes of diffusional echo attenuations and dependencies of apparent self-diffusion coefficients of water and olygomer confined in pores on diffusion time, shows that the porous geometry of the hardened gypsum prepared from calcium hemihydrate and anhydrite can be represented by a model of randomly oriented layers. In the case of hemihydrate, most of the pores are arranged in the macropores range. In the case of pure anhydrite, the fraction of macropores is about 90% and diminishes to 30% as a result of modification. The rest of the pores (10%–30%) are arranged in the mesopores range. This has been established for the first time for the hardened gypsum. The length of pores along the layer was also estimated. In the case of hemihydrate, this value was more than 2.5×10^–5 m, and in the case of anhydrite it was about 0.5×10^–6 m. It is found that the use of modifiers results in a decrease in the layer thickness and permeability of the hardened gypsum.