István Furó

Diffusion-diffusion correlation and exchange as a signature for local order and dynamics

We demonstrate the use of new two-dimensional nuclear magnetic resonance experiments in the examination of local diffusional anisotropy under conditions of global isotropy. The methods, known as diffusion-diffusion correlation spectroscopy and diffusion exchange spectroscopy, employ successive pairs of magnetic field gradient pulses, with signal analysis using two-dimensional inverse Laplace transformation. Diffusional anisotropy is measured for water molecules in a polydomain lamellar phase lyotropic liquid crystal, 40 wt % nonionic surfactant C10E3 (C10H21O(CH2CH2O)6H) in H2O.

Quantifying Mass Transport during Polarization in a Li Ion Battery Electrolyte by in Situ 7Li NMR Imaging

Poor mass transport in the electrolyte of Li ion batteries causes large performance losses in high-power applications such as vehicles, and the determination of transport properties under or near operating conditions is therefore important. We demonstrate that in situ (7)Li NMR imaging in a battery electrolyte can directly capture the concentration gradients that arise when current is applied. From these, the salt diffusivity and Li(+) transport number are obtained within an electrochemical transport model. Because of the temporal, spatial, and chemical resolution it can provide, NMR imaging will be a versatile tool for evaluating electrochemical systems and methods.

Micelle size and order in lyotropic nematic phases from nuclear spin relaxation

Nuclear magnetic resonance (NMR) relaxation of quadrupolar nuclei is introduced as a new method for determining micelle size and nematic order in lyotropic nematic mesophases from the dependence of the spin relaxation rates on molecular diffusion over the curved micelle surface. The approach is illustrated by an experimental study of two uniaxial nematic phases (the calamitic NC and discotic ND phases of the sodium dodecyl sulphate/decanol/water system) using two nuclei: 2H in the α‐deuterated surfactant and 23Na in the counterions. The two nuclei yield similar results: an apparently temperature independent axial ratio of 3–4 in both phases and a nematic order parameter which decreases from ca. 0.9 (0.75) at the lowest temperature to ca. 0.6 (0.5) at the highest temperature in the NC (ND) phase. As compared to the predictions of the Maier–Saupe theory, the nematic order parameter in the NC phase is considerably larger and decreases more strongly as the nematic–isotropic transition is approached.

The morphology of coexisting liquid and frozen phases in porous materials as revealed by exchange of nuclear spin magnetization followed by 1H nuclear magnetic resonance

At low temperatures, liquids imbibed into nanoporous materials form frozen solid cores in the interior of pores. Inbetween the cores and the pore walls, there exists a layer of nonfrozen liquid. As ...

Nuclear spin relaxation in a hexagonal lyotropic liquid crystal

The hexagonal (E) phase in the sodium dodecyl sulphate (SDS)/decanol/water system is investigated by 2H and 23Na nuclear magnetic resonance (NMR) of the selectively deuterated SDS and the sodium counterion. Using macroscopically oriented E phase samples, prepared from the magnetically aligned nematic (NC) phase, we measure the orientation‐dependent relaxation rates R1Z and R1Q as well as the line shape of both nuclei. The orientation dependence of the lab‐frame spectral densities, determined from the relaxation rates, allow us to separate contributions from different types of molecular motion. In particular, we find a dominant contribution from molecular diffusion around the cylindrical aggregate. From this contribution we determine the lateral diffusion coefficient of SDS to (1.4±0.2)×10−10 m2 s−1 at 25 °C (activation energy 26±2 kJ mol−1 ) and the counterion surface diffusion coefficient to (4.8±0.9)×10−10 m2 s−1 at 25 °C (a factor 2.8 smaller than in an infinitely dilute aqueous electrolyte solution). ...

Towards novel wood-based materials: Chemical bonds between lignin-like model molecules and poly(furfuryl alcohol) studied by NMR

Abstract Wood modification with furfuryl alcohol is a non-toxic alternative to conventional preservation treatments. A process in which furfuryl alcohol polymerises in situ was previously proposed for chemical modification of wood. In the present work, liquid model systems were investigated using compounds that resemble repeating units of lignin to verify whether chemical bonds form between the furfuryl alcohol polymer and wood. Using different NMR spectroscopic techniques we confirmed that these model compounds do form covalent bonds with the polymerising polymer. The results indicate that the furan polymer grafts to lignin, supporting observations in similar studies performed with genuine wood materials.

Spin relaxation of I>1 nuclei in anisotropic systems. I. Two‐dimensional quadrupolar echo Fourier spectroscopy

The response, in the frequency domain, of half‐integral spin I>1 nuclei in anisotropic systems to the quadrupolar echo (QE) pulse sequence (π/2)x−τ−(π/2)y is investigated, with particular emphasis on the effects of quadrupolar relaxation. Using a state multipole formalism, we derive the frequency spectra produced by one‐ or two‐dimensional Fourier transformation. Powder samples as well as uniformly and partially oriented samples are considered. The 2D QE experiment produces, in the F1 dimension (Fourier transformation with respect to τ), spectra which provide information about the static quadrupole coupling even if only the central line in the QE spectrum (obtained by Fourier transformation of the induction signal after the echo) is detected. For partially oriented and (incompletely dephased) powder samples, the F1 spectra allow the motional spectral densities to be determined with little or no effect of the inhomogeneous quadrupole coupling, which severely complicates the analysis of conventional (single...

Anisotropic self-diffusion in the nematic phase of a thermotropic liquid crystal by 1H-spin-echo nuclear magnetic resonance

The orientation-dependent molecular diffusion in the nematic liquid crystal 4-pentyl-4′-cyanobiphenyl is measured to high accuracy. The applied nuclear magnetic resonance method combines multiple-pulse homonuclear dipolar decoupling with pulsed-field-gradient stimulated echo and slice selection. The obtained temperature dependencies of the principal diffusion coefficients are not described by a simple Arrhenius relationship but reflect the decrease of the molecular orientational order close to the nematic-to-isotropic phase transition. The geometric average of the principal diffusion coefficients is continuous with the diffusion coefficient in the isotropic phase. The results are best described in terms of the affine transformation model of diffusion in hard-ellipsoid nematics.The orientation-dependent molecular diffusion in the nematic liquid crystal 4-pentyl-4′-cyanobiphenyl is measured to high accuracy. The applied nuclear magnetic resonance method combines multiple-pulse homonuclear dipolar decoupling with pulsed-field-gradient stimulated echo and slice selection. The obtained temperature dependencies of the principal diffusion coefficients are not described by a simple Arrhenius relationship but reflect the decrease of the molecular orientational order close to the nematic-to-isotropic phase transition. The geometric average of the principal diffusion coefficients is continuous with the diffusion coefficient in the isotropic phase. The results are best described in terms of the affine transformation model of diffusion in hard-ellipsoid nematics.

2D Quadrupolar-echo spectroscopy with coherence selection and optimized pulse angle

Abstract The recently developed 2D quadrupolar-echo (QE) method for relaxation studies on I > 1 nuclei in anisotropic systems is generalized and extended. It is shown that by cycling the phase of the refocusing pulse, so that the conjugate dipolar single-quantum coherences are interchanged rather than mixed, linear as well as quadratic terms in the spin Hamiltonian are refocused. With this extension, the 2D QE method can be used to determine the transverse relaxation rates associated with the different Zeeman transitions even in the simultaneous presence of large quadrupolar and magnetic field inhomogeneities. Further, it is shown that by using an optimized refocusing pulse angle, rather than the conventional π 2 pulse, one can substantially improve the signal-to-noise ratio and, at the same time, reduce or eliminate spectral lines that may otherwise cause overlap problems. For I > 3 2 nuclei the refocused intensity can increase with decreasing pulse angle, in contrast to the case of I = 1 and I = 3 2 nuclei, where it decreases as sin3θ Thus, small pulse angles can also be profitably used to increase the excitation bandwidth for I > 3 2 nuclei in systems with large quadrupole splittings.

Polymer binding to carbon nanotubes in aqueous dispersions: residence time on the nanotube surface as obtained by NMR diffusometry.

The binding of block copolymer Pluronic F-127 in aqueous dispersions of single- (SWCNT) and multiwalled (MWCNT) carbon nanotubes has been studied by pulsed-field-gradient (PFG) (1)H NMR spectroscopy. We show that a major fraction of polymers exist as a free species while a minor fraction is bound to the carbon nanotubes (CNT). The polymers exchange between these two states with residence times on the nanotube surface of 24 ± 5 ms for SWCNT and of 54 ± 11 ms for MWCNT. The CNT concentration in the solution was determined by improved thermal gravimetric analysis (TGA) indicating that the concentration of SWCNT dispersed by F-127 was significantly higher than that for MWCNT. For SWCNT, the area per adsorbed Pluronic F-127 molecule is estimated to be about 40 nm(2).