Sedimentary Crystals of Magnetic Hematite Cubes and the Influence of an External Magnetic Field
The structure of spontaneously formed crystals in the sediments of colloidal hematite cubes and silica coated hematite cubes is studied using small angle X-ray scattering (SAXS). The cube interactions were modified by dispersing the cubes in different solvents. The particles were allowed to form sediments under the simultaneous effect of the gravitational field and in a number of cases in an external magnetic field. The SAXS measurements revealed that by increasing the double layer repulsion, that opposes the magnetic and Van der Waals attractions, ordering can be induced in the sedimenting systems of the cubes. The presence of an external magnetic field during sedimentation induced the formation of a single crystal structure with long-range order, that showed different symmetries, four-fold or six-fold, close to the fluid-solid interface.
KeywordsBragg Peak Cube Size Double Layer Repulsion Bragg Spot Gravitational Compression
Dmytro Byelov and Laura Rossi are thanked for their collaboration on this project and the many discussions and useful suggestions for this chapter. The Netherlands Organization for Scientific Research (NWO) and the European Synchrotron Radiation Facility (ESRF) in Grenoble are thanked for the provided beam-time. G. Portale and D. Detolenaire from BM26 and A. Snigirev, I. Snigireva, C. Detlefs and T. Roth from ID06 are thanked for their support during the experiments. For their assistance during the measurements Jan Hilhorst, Anke Leferink op Reinink and Mark Vis are thanked. For their contributions to the particle syntheses Sonja Castillo, Vera Meester, Lisette Pompe, Julius de Folter and Fabian Hagemans are thanked. Part of this work is reproduced by permission of The Royal Society of Chemistry (RSC) .
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