Quasi-elastic neutron scattering adsorbates

Molecules adsorbed within micropores have motional modes and frequencies of re-orientation that depend on the geometric constraints of the pores and the strength of the adsorption interaction. Deuterium ( H) wideline spectroscopy is one of the most powerful experimental methods to study this quasi-elastic neutron scattering is another. Molecular dynamics simulations are also of great value, as described in Section 4.5.3, although the timescales involved only extend to nanoseconds, rather than the timescale of microseconds or greater that is accessible to NMR measurements. 

Scattering Techniques. The thickness of adsorbed layers can be determined using light. X-ray, and neutron scattering techniques (3). Quasi-elastic light scattering measurements on dispersion of particles measure the diffusion coefficients of particles in the dispersion. The size of these particles is related to the diffusion coefficient by the Stokes-Einstein equation. This measurement is performed on the dispersion with and without the adsorbed polymer. The difference in the radii in the two measurements is the thickness of the adsorbed layer. In these measurements it should be ensured that the particles in the dispersion are monodisperse and that there is no flocculation. In X-ray and neutron... 

Additionally, calculation of the diffusion coefficient Z) of an adsorbed layer, based on the analytical solution of Pick s law of diffusion for desorption processes in liquids, in temperature range of 20-200 °C were made for liquids/ montmorillonite-Na and -La samples [38]. The D parameters of the tested materials are presented in Table 8 and they are close to the value presented in the literature. Gay-Duchnal et al. [59] used quasi-elastic incoherent neutron scattering (QINS) to study the diffusion of interlayer water in partially oriented montmorillonite-Na samples and a diffusion coefficient Z) = 1.3 x 10 s was... 

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