Rotational diffusion in concentrated platelet systems measured with X-ray photon correlation spectroscopy.

Using X-ray photon correlation spectroscopy we have measured the rotational modes of concentrated charged gibbsite platelets in the isotropic regime. This has been done by analyzing the data qualitatively using available theories for non-interacting systems. The relaxation spectra do not follow the same pattern as for spherical particles at larger wave vectors.

Nonlinear behavior of nematic platelet dispersions in shear flow.

Dispersions of platelets in the nematic phase are submitted to large amplitude oscillatory shear flow and probed by high temporal resolution small angle x-ray scattering. The response displays rich dynamic and structural behavior. Under small amplitude deformations we observe an elastic response, while structurally symmetry is broken: a preferential direction of deformation is selected which induces off-plane orientation of the platelets.

Effects of added silica nanoparticles on hectorite gels.

We present a study on the macroscopic, microscopic, and rheological behavior of mixtures of natural hectorite clay and different types of anionic Ludox silica spheres. Adding silica spheres to the weak hectorite gels leads the collapse of the suspensions, while the strong gels remain space-filling, though their storage modulus and the yield stress values diminish. We discuss what kind of structural rearrangements are possibly responsible for the macroscopic and rheological changes in the clay/silica mixtures.

Shear-affected depletion interaction.

We investigate the influence of flow fields on the strength of the depletion interaction caused by disc-shaped depletants. At low mass concentration of discs, it is possible to continuously decrease the depth of the depletion potential by increasing the applied shear rate until the depletion force is not perceivable experimentally. Above a threshold in the platelet mass concentration, the depletion potential can no longer be affected by flow in the accessible range of shear rates.

Lyotropic smectic B phase formed in suspensions of charged colloidal platelets.

Here, we present the first observation of a smectic B (Sm(B)) phase in a system of charged colloidal gibbsite platelets suspended in dimethyl sulfoxide (DMSO). The use of DMSO, a polar aprotic solvent, leads to a long range of the electrostatic Coulomb repulsion between platelets. We believe this to be responsible for the formation of the layered liquid crystalline phase consisting of hexagonally ordered particles, that is, the Sm(B) phase.

3D structure of nematic and columnar phases of hard colloidal platelets.

We present small angle x-ray scattering data of single-domain nematic and columnar liquid crystal phases in suspensions of sterically stabilized gibbsite platelets. The measurements are performed with different sample orientations to obtain information about the three-dimensional structure of the liquid crystalline phases. With the x-ray beam incident along the director of the nematic phase a strong correlation peak is observed corresponding to the side-to-side interparticle correlations, which suggests a columnar nematic structure.

The role of the N-terminal domain in dimerization and nucleocytoplasmic shuttling of latent STAT3.

STAT3 is an important transcription factor involved in immunity and cancer. In response to cytokine stimulation, STAT3 becomes phosphorylated on a single tyrosine residue. Tyrosine-phosphorylated STAT3 accumulates in the nucleus, binds to specific DNA response elements and induces gene expression.

Structures and phase behavior in mixtures of charged colloidal spheres and platelets.

The experimental phase diagram for aqueous mixtures of charged gibbsite platelets and silica spheres is presented. The platelets are 95 nm in diameter, and the diameter ratio between the spheres and the platelets is 0.18.

Interaction potential and near wall dynamics of spherical colloids in suspensions of rod-like fd-virus.

Averaged diffusivities of spherical colloids in solutions of rod-like particles, i.e. fd-virus, were measured with EWDLS and TIRM.

Unexpected slow near wall dynamics of spherical colloids in a suspension of rods.

In this paper, we will show the influence of an additional rodlike component, that is, fd-virus, on the diffusion of spherical polystyrene colloids close to a wall. The sphere diffusivity normal to the wall, D perpendicular, is strongly affected by the presence of the rods, while the effect on the parallel diffusivity, D||, is less pronounced except in the immediate vicinity of the wall. We show that this observation cannot be explained by describing the effect of the rods as a simple mean field depletion potential alone.

Steric repulsion by adsorbed polymer layers studied with total internal reflection microscopy.

Total internal reflection microscopy (TIRM) was applied to measure the interaction potential between charge-stabilized polystyrene latex spheres and a glass wall in dependence on the concentration of additional poly(ethylene oxide). The influence of the polymer can be described by steric repulsion between polymer layers, which are physically adsorbed onto the surfaces of the polystyrene sphere and the glass wall. The expected attractive contribution to the potential due to polymer depletion was not observed.

Depletion interaction mediated by a polydisperse polymer studied with total internal reflection microscopy.

Total internal reflection microscopy (TIRM) was applied to measure depletion forces between a charged colloidal sphere and a charged solid wall induced by dextran, a nonionic nonadsorbing polydisperse polysaccharide. The polymer size polydispersity is shown to greatly influence the depletion potential. Using the theory for the depletion interaction due to ideal polydisperse polymer chains, we could accurately describe the experimental data with a single adjustable parameter.

Interactions and two-phase coexistence in nonionic micellar solutions as determined by static light scattering.

We suggest semi-phenomenological approaches for the pair interaction potential in aqueous C(m)E(n) solutions. These expressions are non-linear least squares fitted to static light scattering data from solutions of C(m)E4 and C(m)E8 surfactants in the long wavelength limit. From the resulting interaction parameters we calculate the location of the liquid/liquid two phase coexistence curves, which are in very good agreement with experimental data reported by others.