Quasi-elastic neutron-scattering experiments

To date, incoherent quasi-elastic neutron scattering experiments on the a-relaxation regime of glass-forming polymers have revealed the following main features for the self-motion of hydrogens ... 

In this section we shall show that the joint use of RMT and AEP succeed in explaining the strong deviation from Pick s law observed in quasi-elastic neutron scattering experiments, that is, the appearance of super-Bumett coefficients. ... 

Neutron spin-echo is an experimental technique which allows for quasi-elastic neutron scattering experiments with an extremely high energy resolution (in the range of neV). This is achieved by exploiting the magnetic moment of the neutrons. In a neutron spin-echo... 

The model presented above is in accord with all our experimental results. A more detailed analysis, taking into account the quantitative aspects of the water motion obtained from the quasi-elastic neutron scattering experiments, will be presented in the near future (5). 

To correlate the adsorption and diffusion properties to the cation distribution in the structure of CaNaA zeolites, temperature programmed desorption, anomalous X-ray powder diffraction and quasi elastic neutron scattering experiments were performed. It is shown that water adsorption and diffusion behaviour differs with the calcium content. Fourier maps obtained from anomalous diffraction experiments near the Ca K-edge allow to identify the calcium crystallographic sites unambiguously. 

Best et al. developed another model based on electrostatic phenomena. Owing to the difference in dielectric constant between the PEO and the fillers, polarisation may occur around the fillers. Such a strong interaction may restrict polymer mobility, which is in accordance with the results of quasi-elastic neutron scattering experiments. The cation,due to its localised charge, will show a relatively stable potential landscape, meaning that the potential at the ceramic surface will be of the same order as that at the polymer. The cation will move as the potential barrier is lowered by the filler. 

To compare the calculated values of the linewidth of the principal Lorentzian Xg(A ) with those obtained by quaa-elastic neutron scattering, we have carri out the calculation using the same k values as in these experiments. The calculated Xo(A ) values and the experimental linewidth A (k ) of the corrected quasi-elastic neutron-scattering line are shown in Fig. 12. The calculated deviation from Pick s law appears to be higher than... 

Quasi-elastic neutron scattering (QNS)65 is potentially valuable for investigating the details of rapid H2/hydride atom exchange. QNS is actually a form of INS in which experiments are carried out at higher temperatures in the regime where... 

This work shows that the observation of motions which occur on different time scales can be made from quasi-elastic neutron scattering by performing experiments on spectrometers working at different energy resolutions. It shows that QNS is a very powerful tool to study the spatial dependence of H-motions and that models for the motions can be easily formulated starting from structural results. 

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. 

Elastic and quasi-elastic (NSE) neutron scattering experiments were performed on dilute solutions of linear poly(isoprene) (PIP) polymers and of PIP stars (f = 4,12,18) [150]. In all cases the protonated polymers were dissolved in d-benzene and measured at T = 323 K, where benzene is a good solvent. Figure 50 shows the results of the static scattering profile in a scaled Kratky representation. In this plot the radii of gyration, obtained from a fit of the... 

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