8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P5.106Wed 711:10-14:003D ordering of colloidal cubesJanne-Mieke Meijer, 1 Dmytro Byelov, 1 Laura Rossi, 1 Albert Philipse, 1 and AndreiPetukhov 11 Utrecht University - Van ’t Hoff Laboratory for Physical and Colloid Chemistry,Padualaan 8, 3584 CH, Utrecht, NetherlandsThe structure of colloidal crystals spontaneously formed in sedimented dispersions of colloidalhematite (α − Fe 2 O 3 ) cubes is studied using small-angle x-ray diffraction with microradian resolution.Due to roundness of the cube corners, the particle shape can be best described by a superballshape. This specific type of anisotropic colloids has recently attracted significant attention.In particular, Torquato et al. predicted the optimal packing of superballs by simulations [1] andexperiments of Rossi et al. showed the formation of cubic crystals induced by tunable depletionattraction [2]. The hematite particles used in this study possess a permanent magnetic dipole moment,which provides an additional control factor. The microradian x-ray diffraction reveals longrange periodic ordering in the sedimented systems. In the experiments the particle interactionswere varied by coating the surface with a silica layer and/or dispersing the particles in differentsolvents. Furthermore the systems were examined in the presence of external magnetic field. Thepresence of charge on the particles surface is found to induce ordering in the system. Large singledomaincrystals are obtained using particle alignment in an external magnetic field, which alloweda single-crystal diffraction study. The identified 3D structures were found to be similar to thosearising from simulations.[1] Y. Jiao, F. H. Stillinger, S. Torquato, Physical Review E 79, 041309 (2009)[2] L. Rossi, S. Sacanna, W. T. M. Irvine, P. M. Chaikin, D. J. Pine, A. P. Philipse, Soft Matter 7,4139-4142 (2011)106