Molecular Dynamics Incoherent Neutron Scattering

The study of molecular dynamics in polymers is of great interest because the structural changes of the crystal lattice are intimately related to the onset of molecular motions which generate a special type of dynamical disorder within the crystals [101-104]. In this final section, we prerent an experimental account of the molecular dynamics of copolymers with 60/40 and 80/20 VF2/F3E mole fraction composition using incoherent quasielastic neutron scattering. 

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Some variations in the phonon density of states (DOS) in translational and librational mode regions were studied by inelastic incoherent neutron scattering (IINS) and also studied by molecular dynamics (MD) . For the spectroscopic studies of phonons in XI phase, only a few studies have been reported . We have reported several studies on Raman spectra in the proton ordered XI phase However, detailed mode assignment has not been made successfully yet because of the difficulties to get a single crystal which undergoes the Ih-XI transition with enough transparency suitable for Raman measurement. 

Tarek M, Tobias DJ The dynamics of protein hydration water A quantitative comparison of molecular dynamics simulations and incoherent neutron scattering experiments. Biophys. J. 2000, 79 3244-3257. 

MOLECULAR MOTIONS OF HYDROCARBON CHAINS (DECYLAMMONIUM,n-NONADECANE) IN THEIR DYNAMICALLY DISORDERED PHASES AN INCOHERENT NEUTRON SCATTERING STUDY... 

Figure 8 Inelastic incoherent neutron scattering spectra for methane hydrate (a) translational vibration (b) quantum rotation and (c) comparison with molecular dynamics calculations. Reprinted (adapted) with permission from /. Fhys. Chem. A, 101, 4491 (1997). Copyright 1997 American Chemical Society.

The prerequisite for an experimental test of a molecular model by quasi-elastic neutron scattering is the calculation of the dynamic structure factors resulting from it. As outlined in Section 2 two different correlation functions may be determined by means of neutron scattering. In the case of coherent scattering, all partial waves emanating from different scattering centers are capable of interference the Fourier transform of the pair-correlation function is measured Eq. (4a). In contrast, incoherent scattering, where the interferences from partial waves of different scatterers are destructive, measures the self-correlation function [Eq. (4b)]. 

The above molecular dynamics results have been confirmed by incoherent inelastic neutron scattering (IINS) measurements on xenon hydrate (Tse et al., 2001 Gutt et al., 2002). In earlier measurements on methane hydrate, the dominant... 

B. Winkler B. Hennion (1994). Phys. Chem. Minerals, 21, 539-545. Low temperature dynamics of molecular H2O in bassanite, gypsum and cordierite investigated by high resolution incoherent inelastic neutron scattering. 

Inelastic neutron scattering is a technique that has been widely used both in the liquid and in the solid states to measure the stmcture and dynamics at small (that is, molecular) length scales. In an incoherent inelastic neutron-scattering experiment, the measured quantity is the self-dynamic structure factor Ss(Q, (o), which gives information, as in the liquid state, of the self-diSiision coefficient of the water molecules. Ss(Q, (o) is the Fourier transform of the intermediate self-scattering function Fg(Q, t), which is defined by... 

Several techniques have been used to investigate dynamic properties of urea inclusion compounds, including solid-state NMR, incoherent quasielastic neutron scattering ESR, molecular dynamics simulation, Raman, infrared, dielectric loss, and x-ray diffraction. In addition to investigations of the dynamics of the guest molecules, the dynamic properties of the urea molecules have also been studied. 

Quasi-elastic Neutron Scattering. Coherent and incoherent inelastic neutron scattering are unique experimental techniques to characterize molecular motions on a time scale between 10 and 10 s. The continued development of high resolution inelastic scattering techniques in the past two decades (157-159) enables measurement of the dynamic structure factor S(Q, co) and the... 

BordaUo HN, Zakharov BA, Boldyreva EV, Johnson MR, Koza MM, Seydel T, Fischer J (2012) Application of incoherent inelastic neutron scattering in pharmaceutical analysis relaxation dynamics in phenacetin. Mol Pharm 9 2434-2441 Bptker JP, Karmwar P, Strachan CJ, Cornett C, Tian F, Zujovic Z, Rantanen J, Rades T (2011) Assessment of crystalline disorder in cryo-milled samples of indomethacin using atomic pairwise distribution functions. Int J Pharm 417 112-119 Boutonnet-Fagegaltier N, Menegotto J, Lamure A, Duplaa H, Caron A, Lacabanne C, Bauer M (2002) Molecular mobihty study of amorphous and crystalline phases of a pharmaceutical product by thermally stimulated current spectrometry. J Pharm Sci 91 1548-1560 Bras AR, Noronha JP, Antunes AMM, Cardoso MM, Schdnhals A, Affouard Fdr, Dionfsio M, Correia NIT (2008) Molecular motions in amorphous ibuprofen as studied by broadband dielectric spectroscopy. J Phys Chem B 112 11087-11099... 

A. Incoherent inelastic neutron scattering measurements [53] gave some evidences that the boson peak is a localized mode on 6 and 11 monomers for PS and PB, respectively. Such localization was predicted in molecular dynamics simulations [54-56]. In the framework of the soft potential model, which will be mentioned later, the number of atoms participating in the boson peak mode was evaluated, showing the localization of the boson peak mode on several tens to hundreds of atoms for three inorganic glasses [28] and on several monomers for three polymers [57]. 

The same incoherent quasi-elastic neutron scattering methods have been used to probe the molecular dynamics of more complex systems. Fatty acid salts of copper form a disk-like molecule comprising a binuclear core with four chains extending from it, and these can form a columnar mesophase where the disks are stacked. Copper palmi-tate has been examined in its crystalline phase and in a columnar mesophase. The quasi-elastic scattering was interpreted in terms of the motion of the alkyl chains. Each methylene group explored a spherical volume and the radius of the sphere increased with distance from the copper core [68], A later experiment on oriented fibers of copper laurate [69] showed that this motion was anisotropic with a greater amplitude in the plane perpendicular to the columns. 

Incoherent quasi-elastic neutron scattering (IQENS) has been used to investigate the dynamics of nematic phases. When a monochromatic beam of neutrons is scattered from a nematic liquid crystal the shape of the elastic line in the energy-transfer spectra gives information on the molecular dynamics. A quasi-elastic neutron scattering measurement may be used to investigate the diffusive motions of the molecules in the nematic phase. The translational diffusion coefficients may be determined and localised motions such as molecular rotation and internal rotations may also be characterised. 

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