Electrophoretic light scattering in the presence of electroosmosis is investigated both experimentally and theoretically. For a rectangular scattering cell, a wide range of inhomogeneously broadened light-scattering spectra is reported, which can fully be accounted for by theoretical expressions derived in the paper. For one selected colloidal suspension, it is demonstrated that the results obtained by this electrophoretic-electroosmotic light-scattering technique are in quantitative agreement with results obtained by the method of microelectrophoresis.
Light diffraction from shear ordered colloidal dispersions is discussed in terms of the scattering power distribution I(l) along Bragg rods of hexagonal layers. For a charge stabilized dispersion the angle dependence of the light scattering intensity is used to determine I(l), from which conclusions on the mutual registration of the layers, the stacking order, and the kinetics of crystallization can be drawn. For the system under study a structural transition from random close-packed hexagonal layers to faulted twinned fcc is identified. [S0031-9007 (97)02367-3] PACS numbers: 82.70.DdThe equilibrium phase behavior of charge stabilized colloidal dispersions has been investigated as a function of particle concentration and ionic strength [1-4]. At low particle concentration and low ionic strength the equilibrium structure is liquidlike or bcc. A region of fcc follows at higher particle concentration and ionic strength. At very high particle concentration, finally, glasslike behavior has been observed [2], the ultimate equilibrium structure of which is not yet known. After the application of shear, such dispersions often show a high degree of order which, according to small angle neutron scattering (SANS) experiments [5-7], is not in agreement with the above mentioned equilibrium structures [8,9]. It has therefore been proposed to consider hexagonal layers as the basic structure element for concentrated shear ordered colloidal dispersions [8][9][10][11][12]. The threedimensional structure obtainable from such layers depend on (a) the packing of the layers and (b) the stacking sequence of the layers [13].By measuring the SANS Bragg spot intensity at various sample orientations we were recently able to determine the scattering intensity I hk ͑l͒ along Bragg rods with Miller indices (h, k) [9,12]. In the present letter we show that the method of determining the intensity distribution I hk ͑l͒ along Bragg rods of shear ordered dispersions can be extended to light scattering (LS). First, we present explicit experimental determinations of I hk ͑l͒ by light scattering and show further how the structure of dispersions and the kinetics of recrystallization after the application of shear can be investigated by this method. We also mention that light scattering "powder" diffraction from hard sphere colloidal systems has been interpreted in terms of close-packed random stacking layers [14,15].Our experiments were performed with polystyrene latex dispersions, charge stabilized by sulfat surface groups. The particle diameter was s 240 nm with a polydispersity of about 6% as determined by transmission electron microscopy. Ordering of the dispersions was achieved by first completely deionizing the sample with ion exchange resins and then applying shear. For this the dispersion was filled in a rectangular quartz cell of dimensions 0.5 mm thickness 3 10 mm width 3 40 mm length, equipped with an inlet and an outlet through which flowing was achieved by means of a peristaltic pump. The cell was mounted on a rotation stage which allowed...
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