Shear-Induced Order in Aqueous Micellar Solutions of Amphiphilic Poly(tert-butylstyrene)-b-poly(Na methacrylate) Diblock

Calculation of scattering-patterns of ordered nano- and mesoscale materials

Analytical expressions for the scattering patterns of ordered nano- and mesoscopic materials are derived and compared to measured scattering patterns. Ordered structures comprising spheres (fcc, bcc, hcp, sc, and bct), cylinders (hex and sq), lamellae (lam) and vesicles, as well as bicontinuous cubic structures (Ia3d, Pn3m, and Im3m) are considered. The expressions take into account unit cell dimensions, particle sizes and size distributions, lattice point deviations, finite domain sizes, orientational distributions, core/shell-structures as well a variety of peak shapes. The expressions allow to quantitatively describe, model and even fit measured SAXS and SANS-patterns of ordered or oriented micellar solutions, lyotropic phases, block copolymers, colloidal solutions, nanocomposites, photonic crystals, as well as mesoporous materials.

Rotational manipulation and stacking of nanosystems

In this paper two kinds of Bragg reflections from oriented mesogenic crystals are considered. Bragg reflections behave differently for ...ABABA... and ...ABCABCA... layer stacking. We call them black and white reflections. Black reflections are characterized by the fact that they behave identical for the two kinds of stacking. Therefore, the message is the following: Black rods should not be used to identify the two kinds of stacking. By contrast, white reflections show a different behavior for ...ABABA... and ...ABCABCA... stacking and for the resulting hexagonal close-packed (hcp) and face-centered cubic (fcc) crystals. White reflections can be used to distinguish the two kinds of crystals. For an application of this method the crystals should be oriented. It will be shown that orienting by flow is possible in a Couette cell. Flow ordering occurs in all rotation cells which are often applied in rheology. The scattering presented is therefore closely related to rheology. Details and experimental results will be given in the paper.

Order causes secondary Bragg peaks in soft materials

Highly ordered soft materials exhibit Bragg peaks that cannot be indexed assuming homogeneous crystal structures. Their origin has been attributed to changes in the crystal structure that are induced by the ordering process such as by application of external fields. This would restrict the use for the generation of highly ordered nano- and microstructured materials where a homogeneous crystal structure is a key requirement. Here, we demonstrate that these Bragg peaks are an inherent property of homogeneous ordered soft materials related to the finite coherence of their crystalline lattice. Their consideration allows a detailed and quantitative analysis of the diffraction patterns of seemingly unrelated materials such as lyotropic liquid-crystalline phases, mesoporous materials, colloidal dispersions, block copolymers, electrorheological fluids and photonic crystals. It further enables us to develop a concise picture of order, line density, field-induced orientation and epitaxial relations for soft-material lattices.

On the Structure of Shear-Ordered Polymer Dispersions

The present paper is concerned with the structure of colloidal dispersions consisting of charged polymer particles. The scattering of light, neutrons or X-rays from such latex dispersions is best described in the reciprocal lattice. Two quantities of central importance will be introduced: the particle form factor P(Q) and the interparticle structure factor S(Q). In the present treatment we show that the structure can be adequately accounted for by introducing a redefined symmetry adapted aggregate structure factor. According to the structure of interest these aggregate structure factors are one-dimensional (string-like), two-dimensional (layer-like) or three-dimensional (crystal-like). The description appears particularly suited to account for systems under sheared conditions. In the final section we present experimental neutron scattering results. A structural change is observed as a function of the shear rate γ°. The occurrence of the structural change and its relation to the 'self´ part of the previously introduced aggregate structure factor are considered.