1,721,143 research outputs found
CAGE: Software for a critical analysis of H-2 spin-lattice relaxation in liquid crystals
No full textA software package of Mathematica, aimed at the analysis of 2H NMR Zeeman (T1Z) and quadrupolar (T1Q) spin-lattice relaxation times in liquid crystals in terms of diffusional models, is presented. The models most commonly used to describe internal, overall, and collective motions in liquid-crystalline phases are considered, and dynamic parameters are obtained by means of either single point or global target approaches using simulation or fitting procedures. The use of the software as a tool for highlighting the problems encountered in this kind of analysis as well as for dealing with such problems following suitable strategies is illustrated by means of applications to experimental 2H relaxation times of three different calamitic liquid crystals
The SPORT-NMR software: A tool for determining relaxation times in unresolved NMR spectra
No full textA software package which allows the correct determination of individual relaxation times for all the nonequivalent nuclei in poorly resolved NMR spectra is described. The procedure used, based on the fitting of each spectrum in the series recorded in the relaxation experiment, should improve the analysis of relaxation data in terms of quantitative dynamic information, especially in anisotropic phases. Tests on simulated data and experimental examples concerning 1H and 13C T1 measurement in a solid copolymer and 2H T1Z and T1Q measurement in a liquid crystal are shown and discussed
Comparison of the dielectric and NMR results for liquid crystals : dynamic aspects
No full textCritical analysis of the results of studies of molecular rotational dynamics in liquid crystalline substances with the aid of the dielectric spectroscopy (DS) and nuclear magnetic resonance (NMR) is given. Both methods are known to be sensitive to different aspects of molecular rotations: the polarization vector and the relaxation time (DS) in the case of DS, a tensor describing a nuclear interaction and the correlation time (NMR) for NMR method. Furthermore, both methods provide correlation functions with different rank values. A common basis for the comparison between (DS) and (NMR) is postulated. Several examples of the temperature dependence of the correlation times coming from the two spectroscopic methods are presented. Qualitative agreements of the correlation times were achieved in most cases
STUDY OF THE MOLECULAR-DYNAMICS FROM DEUTERIUM ZEEMAN AND QUADRUPOLAR NMR RELAXATION OF 4,4'-DI-N-HEPTYLAZOXYBENZENE IN THE NEMATIC AND SMECTIC-A PHASES
No full textMethods for correlating T-1 rho and FID components in wideline H-1 NMR studies of motionally heterogeneous polymer systems
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Phenyl ring dynamics in a liquid crystal polymer through H-2 NMR spectroscopy
No full textThe dynamics of a side chain liquid crystal copolymer at two dierent compositions has been investigated in its smectic A and C phases. J1x0 and J22x0 spectral densities have been determined for aromatic deuterium nuclei in the side chains and their interpretation has been carried out by means of several available motional models. The dy- namic process mainly contributing to relaxation has been found to be the rotation of the phenyl ring about its para-axis, that is best described by a small step rotational diusion model, where the diusion constant has an Arrhenius tem- perature dependence and a Gaussian distribution of the activation energies is present, indicating a remarkable degree of dynamic heterogeneity of this system
A new approach to the extraction of dynamic information from the analysis of H-2 NMR relaxation times in tilted chiral mesophases
No full textA new approach to analyze H-2 spin-lattice relaxation times in tilted smectic phases in terms of dynamic parameters for individual molecular and internal motions is reported. Such analysis, commonly applied to uniaxial phases, could not be extended so far to chiral smectic phases for both experimental and theoretical reasons. These problems have been here overcome neglecting the dependence of spectral densities on the azimuthal angle phi, and adopting a global target approach. In this way, the existing diffusional models can be used to determine dynamic parameters in chiral smectic C phases. An application to the ferroelectric mesogen 8BEF5 is reported
Organic protic ionics based on Nitrilo(trimethylenephosphonic acid) as water-free, proton-conducting materials
No full textWe produced two solid protic ionics by stoichiometric acid-base reaction between Nonafluorobutanesulfonic or p-Toluenesulfonic acid with Nitrilotri(methylenephosphonic acid). The latter behaves as a Bronsted base by means of the nucleophilic nitrogen atom which captures the proton from the Nonafluorobutanesulfonic or p-Toluenesulfonic acid. Moreover, the Nitrilotri(methylenephosphonic acid) moiety possesses six POH terminating units. 1H MAS NMR evidenced hydrogen-bonding activity of these units, which enables proton transport through the lattice by a hopping-site mechanism. Homogeneous, transparent and mechanically and thermally robust disks from these materials were obtained by sintering the powders under mild pressure and temperature. We showed, using electrochemical impedance spectroscopy, that these protic ionics possess good proton conductivity, in excess of 10–2 –1 cm–1, under fully anhydrous conditions at 190 °C. As such, these materials appear potentially attractive for application in high-temperature electrochemical devices, such as polymer electrolyte fuel cells and water electrolyzers operating at elevated temperature, typically above 130 °C and up to 200 °C for fuel cells. The proton-transport mechanism is also discussed in the light of the NMR- and impedance-spectroscopy results
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