Strong anisotropic nematic order in liquid crystal polymers: [4] a quasi-elastic neutron scattering study

From quasi-elastic neutron scattering experiments performed in glassy, nematic and isotropic phases, the dynamics of oriented samples of strong anisotropic side-on fixed liquid crystal polymers have been analysed. Using the selective deuteration method, we are able to attribute motions to specific parts of the molecule in the parallel and perpendicular orientations. The motions of the whole macromolecule decrease as soon as the temperature decreases below the isotropic-nematic transition. Nevertheless, the motions of the polymer backbone, compared to the whole polymer dynamics, are systematically reduced, even in the isotropic phase. Moreover, an anisotropy of the motions is revealed, with a reduction in the direction parallel to the orientation. An harmonic character of the vibrational processes is also evidenced. We conclude that the anisotropy of the dynamic corroborates the anisotropy of conformation of the macromolecule (so-called jacketed structure). Received: 29 October 1997 / Revised: 22 January 1998/ Accepted: 11 May 1998     

Phonon density of states of single-wall carbon nanotubes

The vibrational density of states of single-wall carbon nanotubes (SWNT) was obtained from inelastic neutron scattering data from 0 to 225 meV. The spectrum is similar to that of graphite above 40 meV, while intratube features are clearly observed at 22 and 36 meV. An unusual energy dependence below 10 meV is assigned to contributions from intertube modes in the 2D triangular lattice of SWNT bundles, and from intertube coupling to intratube excitations. Good agreement between experiment and a calculated density of states for the SWNT lattice is found over the entire energy range.     

Water mobility in a water-soaked nafion® membrane: A high-resolution neutron quasielastic study

Water mobility in an acid Nafion® membrane containing ca. 15% water by weight has been studied by high-resolution neutron quasielastic scattering (NQES). The data are analyzed in terms of simple models. On a scale of ca. 10 Å, the water molecules move practically as freely as in bulk water, but their long-range motion is much more hindered. These results are important for an understanding of the relation between the microstructure and the macroscopic properties of these membranes. To our knowledge, this is the first detailed NQES study of the water-polymer interaction problem.     

A quasielastic neutron scattering study of the self-diffusion coefficients for the homologous series of 4,4'-di-n-alkyloxyazoxybenzenes

Incoherent quasielastic neutron scattering measurements performed with high resolution (∼ 1 μcV) have provided the diffusion coefficients for translation of four members of the 4,4'-di-n-alkyloxyazoxybenzene series in their nematic phases. An odd-even effect in these coefficients was observed. The results were compared with those previously obtained by Noack via the NMR technique. There is fairly good agreement between his NMR and our QNS results.     

New data concerning lysozyme from goose egg-white: tryptophan content, stability and sensitivity

New data concerning the tryptophan content, the stability, and the specificity of goose egg-white lysozyme are reported. This enzyme occupies a special place among the mammelian lysozymes already studied and the general definition of a lysozyme had to be modified. The mechanism of action is discussed.     

Molecular dynamics in solid n-nonadecane: Experiments and computer simulations

We have undertaken a collaborative study on the molecular dynamics and the phase transition mechanisms in low-dimensional molecular crystals by combining incoherent quasielastic neutron scattering, deuterium NMR and computer simulation techniques. In this paper, we summarize the method used for deriving a dynamical model for the reorientations of n-nonadecane molecules in the rotator phase R _I of the crystal. This model has been applied successfully to interpret experimental and computational data.     

H-bond dynamics in well-characterized supercooled and glassy aqueous solutions

On the basis of a structural characterization of different thermodynamic states, we investigate the vibrational density of state for a saturated aqueous solution LiCl·RH₂O (R=6 and 4). Intermolecular motions of water deduced from inelastic neutron scattering are discussed. Bending, stretching and vibrational modes exhibit different behaviour in glassy, supercooled and liquid states. Stretching motion appears to be quite sensitive to the glass transition.