We use dynamic light scattering and numerical simulations to study the approach to equilibrium and the equilibrium dynamics of systems of colloidal hard spheres over a broad range of density, from dilute systems up to very concentrated suspensions undergoing glassy dynamics. We discuss several experimental issues (sedimentation, thermal control, non-equilibrium aging effects, dynamic heterogeneity) arising when very large relaxation times are measured. When analyzed over more than seven decades in time, we find that the equilibrium relaxation time, tau_alpha, of our system is described by the algebraic divergence predicted by mode-coupling theory over a window of about three decades. At higher density, tau_alpha increases exponentially with distance to a critical volume fraction phi_0 which is much larger than the mode-coupling singularity. This is reminiscent of the behavior of molecular glass-formers in the activated regime. We compare these results to previous work, carefully discussing crystallization and size polydispersity effects. Our results suggest the absence of a genuine algebraic divergence of tau_alpha in colloidal hard spheres.

We use x-ray photon correlation spectroscopy to investigate the dynamics of a high volume fraction emulsion creaming under gravity. The dodecane-in-water emulsion has interfaces stabilized solely by colloidal particles (silica). The samples were observed soon after mixing: as the emulsion becomes compact we discern two regimes of ageing with a cross-over between them. The young emulsion has faster dynamics associated with creaming in a crowded environment accompanied by local rearrangements. The dynamics slow down for the older emulsion although our studies show that motion is associated with large intermittent events. The relaxation rate, as seen from the intensity autocorrelation function, depends linearly on the wave vector at all times; however, the exponent associated with the line shape changes from 1.5 for young samples to less than 1 as the emulsion ages. The combination of ballisticlike dynamics, an exponent that drops below 1 and large intermittent fluctuations has not been reported before.

Lyotropic nematic aqueous suspensions of single-wall carbon nanotubes can be uniformly aligned in thin cells by shearing. Homogeneous anisotropic thin films of nanotubes can be prepared by drying the nematic. Optical transmission between parallel or crossed polarizers is measured and described in order to estimate the dichroic ratio. The order parameter is measured using polarized Raman spectroscopy and found to be quite weak due to entanglement of the nanotubes and/or to an intrinsic viscoelastic behavior of the nanotube suspensions.

The present work addresses the question of the range and amplitude of bridging attraction that is induced between surfactant micelles functionalized with complexing groups in the presence of coordination centers. An alkylethoxylated ester phosphate (AEP) is synthesized from a non-ionic surfactant and anchored into DTAB micelles. In the absence of any coordination center, functionalized micelles repel each other. Phase behavior, dynamic light scattering and small angle neutrons scattering (SANS) experiments show that this repulsive interaction is switched to attractive by the addition of coordination centers such as aluminum cations. The extent of the composition range of coexisting phase depends on the concentration of coordination center and on the pH. Analysis of the structure factor obtained from SANS shows that the range of attraction is determined by the molecular dimension of the chelating surfactant, while the depth can be tuned with the concentration of coordination center and the pH, The strong influence of the pH is interpreted as arising from the condensation of aluminium cations that lead to high functional polynuclear complexes.

The elastic properties of organic-inorganic two-dimensional crystals floating at the water surface have been fully characterized by grazing incidence X-ray diffuse scattering and high-resolution diffraction. We show that the strong interaction between the organic molecules and the inorganic divalent cations is enough for these nm thick crystals to behave like true solids, with a residual tension of 1 x 10(-4)-10(-3) N m(-1). Their bending rigidity is renormalized as kappa(q) proportional to q(-eta k) with eta(k) = 0.25 +/- 0.07 and a microscopic value approximate to 100 k(B)T at q = 1 x 10(9) m(-1). The in-plane elastic constants behave like q(eta u) with eta(u) = 1.41 +/- 0.2, obeying the scaling relation eta(u) = 2 - 2 eta(k). These results are consistent with a long-range phonon-mediated interaction between out-of-plane fluctuations but the values of the exponents differ from those generally obtained in numerical simulations.

Continuous and simultaneous measurement of the tank-treading motion of red blood cells and the surrounding flow using translational confocal micro-particle image velocimetry (micro-PIV) with sub-micron resolution M Oishi, K Utsubo, H Kinoshita et al. Abstract Microfluidic tools are providing many new insights into the chemical, physical and physicochemical responses of cells. Both suspension-level and single-cell measurements have been studied. We review our studies of these kinds of problems for red blood cells with particular focus on the shapes of individual cells in confined geometries, the development and use of a 'differential manometer' for evaluating the mechanical response of individual cells or other objects flowing in confined geometries, and the cross-streamline drift of cells that pass through a constriction. In particular, we show how fluid mechanical effects on suspended cells can be studied systematically in small devices, and how these features can be exploited to develop methods for characterizing physicochemical responses and possibly for the diagnosis of cellular-scale changes to environmental factors.