Hideki Matsuoka

Surface-Induced Parasitic Scattering in Bonse-Hart Double-Crystal Diffractometers

Bonse-Hart double-crystal diffractometers (DCD) with multibounce channel-cut crystals show rocking curves which depart dramatically in their wings from dynamical diffraction theory. This intrinsic background is many orders of magnitude higher than the predictions of dynamical diffraction theory. This effect has been studied at the ultra-small-angle neutron scattering (USANS) facility at Oak Ridge National Laboratory by the measurement of rocking curves from different volume elements of a thick single-bounce Si(lll) perfect crystal and from triple-bounce channel-cut Si(lll) crystals. Analysis of these data, together with the rocking curves from an X-ray Bonse-Hart DCD, allows it to be established that the rocking curve of the multibounce channel-cut crystals contains parasitic scattering generated at the surface of the crystals. The intensity of this component can be reduced by very deep etching of the crystal surface. Using this technique, the signal-to-noise ratio of the Bonse-Hart DCD at the ORNL USANS facility has been improved by one order of magnitude to ~,5 x 105 [I(0)/I(0 = 10)].

Rotational diffusion of ellipsoidal latex particles in dispersion as studied by depolarized dynamic light scattering

The rotational diffusion coefficient, Θ, of ellipsoidal latex particles of different sizes in a dispersion has been measured by the depolarized dynamic light scattering technique. The measured Θ values were smaller than those calculated from the particle geometry using the Perrin equation. The difference between the experimental and calculated Θ values was larger for the smaller latex particles at constant ionic strength. The effect of the ionic atmosphere around an ellipsoidal latex particle, probably the distortion caused by rotational motion, can be thought to be an origin of this behavior.

The mystery of colloidal crystal formation — novel aspects obtained by ultra-small-angle X-ray scattering

Abstract We describe our recent ultra-small-angle X-ray (USAXS) data for the structure of colloidal crystals. Information on the three dimensional ‘bulk’ structure of colloidal crystals can be obtained using USAXS, and the interparticle distance estimated from the Bragg peak in the USAXS profile shows a maximum as a function of added salt concentration (i.e. ionic strength). Since all types of latex particles used in the experiments show a similar trend, this phenomenon, i.e. the existence of ‘a maximum’, can be said to be universal. This maximum position appears at κa=1.3 (κ−1: the Debye length, a: the particle radius). By theoretically analyzing the USAXS profiles, we have quantitatively estimated the distortion of the lattice structure of colloidal crystals. This analysis revealed that the maximum point corresponds to the ‘melting’ point of colloidal crystals. The dependence of interparticle distance on added salt at κa>1.3, where colloidal particles form liquid-like structures, can be explained by the classical theories, such as the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, but that at κa

The structure of colloidal alloy crystals revealed by ultra-small-angle neutron scattering

Abstract We investigated the structure of colloidal crystals in binary colloidal dispersion by the ultra-small-angle neutron scattering (USANS) technique. The mixed dispersion of deutrated polystyrene latex ( d -PS) and hydrogenated polystyrene latex ( h -PS) dispersions (the size ratio α =0.54) was prepared for the USANS experiment to apply the contrast matching technique. The scattering from the each component could be detected separately. We also extracted the partial scattering intensity I dPS-hPS ( q ) at three mixing ratios. The USANS scattering profiles at the contrast matching point for each component were changed clearly with the change of the mixing ratio of d -PS and h -PS lattices. The I dPS-hPS ( q ) profile obtained for the d -PS number fraction x dPS03 =0.39 indicated the correlation between d -PS and h -PS particles. These USANS observation suggested strongly the formation of the liquid-like colloidal alloy structure in the binary colloidal dispersion.

Direct estimation of interaction potential between phospholipid liposome particle and glass surface by evanescent wave light scattering microscope method

Abstract The potential profile of interaction between a charged liposome particle and glass surface was estimated directly by evanescent wave light scattering microscopy (EVLSM), which can measure the distance between the particle and surface as a function of time at intervals in the order of less than millisecond. The minimum of the potential profile, which is a result of electrostatic repulsion and attraction by gravity, was clearly observed. Liposome particles of different surface charge were prepared by using charged and apparently neutral lipid molecules at various mixing ratios. With the increase in the amount of negatively charged liposomes, the potential minimum in interaction potential shifted further away from the glass surface, reflecting an increase of electrostatic repulsion between them. The potential profile clearly showed ionic strength dependence. We found that the electrostatic interaction is an important factor for particle–surface interaction and that EVLSM is a powerful tool for quantitative estimation of particle–wall interaction.