Quasielastic and Low-Frequency Raman Light Scattering in Lithium Niobate Crystals with Stoichiometric Defects

The paper investigates quasielastic light scattering spectra at a temperature of 296 K in lithium niobate samples of various degrees of imperfection as measured by means of the acoustic quality factor. We performed a quantitative spectrum analysis in the 0--70 cm-1 frequency range for samples with different Q-factor values in a model accounting for the connection between a low-frequency optical mode of the A1(TO) symmetry type and the acoustic density of states observed in a spectrum as a result of violating the wavevector selection rule in a stoichiometrically defective crystal. The results of comparing these simulations to experimental data show that stoichiometrical defects significantly contribute to the quasielastic light scattering intensity in congruent lithium niobate crystals

Quasielastic Light Scattering and Structure of Nanodroplets Mixed with Polycaprolactone

The interaction of polycaprolactone (PCL) with droplets of a microemulsion is studied with quasielastic light scattering and small angle X-ray scattering At constant droplet size we vary the PCL concentration and there is clear evidence for an increasing attractive interaction of the droplets from structural investigations with small-angle X-ray scattering (SAXS). The collective diffusion coefficient (Dc) of the droplets is monitored with quasielastic light scattering (QELS). We mainly focus on the variation of the dynamic behavior as a function of the PCL concentration and length scale (M.W. = 5000 and 10000) in microemulsion. With increasing PCL concentration and length scale the dynamics of the system slow down. A hard sphere model with depletion potential can fit well the SAXS experiment of microemulsion mixed with PCL. The results show with increase of PCL on microemulsion the size of droplets is constant at 83Å but the size ratio of polymer to droplets is changing.