Complex patchy colloids shaped from deformable seed particles through capillary interactions.

We investigate the mechanisms underlying the reconfiguration of random aggregates of spheres through capillary interactions, the so-called "colloidal recycling" method, to fabricate a wide variety of patchy particles. We explore the influence of capillary forces on clusters of deformable seed particles by systematically varying the crosslink density of the spherical seeds. Spheres with a poorly crosslinked polymer network strongly deform due to capillary forces and merge into large spheres. With increasing crosslink density and therefore rigidity, the shape of the spheres is increasingly preserved during reconfiguration, yielding patchy particles of well-defined shape for up to five spheres. In particular, we find that the aspect ratio between the length and width of dumbbells, L/W, increases with the crosslink density (cd) as L/W = B - A·exp(-cd/C). For clusters consisting of more than five spheres, the particle deformability furthermore determines the patch arrangement of the resulting particles. The reconfiguration pathway of clusters of six densely or poorly crosslinked seeds leads to octahedral and polytetrahedral shaped patchy particles, respectively. For seven particles several geometries were obtained with a preference for pentagonal dipyramids by the rigid spheres, while the soft spheres do rarely arrive in these structures. Even larger clusters of over 15 particles form non-uniform often aspherical shapes. We discuss that the reconfiguration pathway is largely influenced by confinement and geometric constraints. The key factor which dominates during reconfiguration depends on the deformability of the spherical seed particles.

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. It will be shown that this deviation from the behavior of spherical systems arises from the influence of the rotational modes. In addition, in the isotropic state a pre-transitional peak in the static q-dependent intensity at large q values is discussed. We suggest that this peak originates from a strong local alignment between platelets before the actual phase transition takes place.