Quasi-elastic scattering approximation

The superscripts Q stands here for quasi-elastic scattering, and the subscript pre means the pre-average approximation. 

We investigate here the dynamic behavior of fully charged NaPSS solutions with multivalent salt (LaCl3) measured by quasi-elastic light scattering. The bimodal decay of the correlation function of polyelectrolyte concentration (C) at constant salt concentration (Cs) is studied first. The ratio Cs/C varies from 0.2 to 10 2. Then the dynamics of the solution at constant C as a function of Cs from Cs/C approximately 10 2 to 0.2 are investigated. 

Coherent quasi-elastic neutron scattering due to the pair-correlation of atomic motions is more complex than incoherent scattering from single particle motion. Therefore, the theory of coherent scattering function is not yet fully developed. However, approximate expressions for the coherent scattering function exist (incoherent approximation). 

In this study we have investigated the structural and interaction parameters of ternary water/octane/CiaEs system by means of SAXS. Phase behavior of this system was studied by Kahlweit et al. [9]. This system shows interesting phase behavior (Fig. 1). One can study the structures of low-temperature microemulsion (LTM) phase, middle-temperature lamellar (MTL) phase and high-temperature microemulsion (HTM) phase by changing temperature only, provided that the sample contains approximately more than 12 wt% of surfactant at equal volume fraction of water and oil. Bodet et al. have clarified the structural evolution of this system by means of pulsed-field gradient spin-echo NMR, quasi-elastic light scattering and freeze-fracture transmission electron microscopy [10]. Local structure of the bilayer and monolayer of the same system was also studied by Strey et al. [11]. Recently, we have studied the mechanism of the phase transition [12]. 

A second ensemble technique is DLS (Nicoli et al, 1991) - also called quasi-elastic light scattering (QELS) or photon correlation spectroscopy (PCS) — which is based on analysis of the temporal fluctuations in the scattered intensity caused by Brownian motion, or diffusion, of the particles. In recent years, it has become a popular technique for characterizing many submicron colloidal systems, including polymer lattices, because of its large size range (roughly 1 nm to 5 p,m) and approximate independence from optical properties. 

The next assumption is that the relaxation time approximation is valid. According to Nag, this is equivalent to the assumption that scattering processes are elastic or isotropic and that quasi-Fermi levels can be used to describe carrier distribution [347]. In that case... 

---