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

Wed 711:10-14:00P5.155Colloidal cubes in an external electric fieldFrank Smallenburg, 1 Rao Vutukuri, 1 Alfons van Blaaderen, 1 and Marjolein Dijkstra 11 Utrecht University, Princetonplein 5, Ornstein Laboratorium 016 3584CC, Utrecht,NetherlandsElectric fields have proven to be a versatile tool for directing colloidal particles into 1D strings,2D sheets and 3D crystal structures [1, 2, 3]. When a suspension of colloidal particles is placedin an oscillating electric field, the contrast in dielectric constant between the particles and thesolvent induces a dipole moment in each of the colloidal particles. The resulting dipole-dipoleinteractions can strongly influence the phase behavior of the system. In addition, most anisotropicparticles can be aligned in electric fields. However, in the case of cubes the potential energy ofa single cube-shaped particle in an electric field is independent of its orientation. As a result,single cubic particles do not align in such an external field. Aligning effects can still occur due tohard-core constraints when multiple particles cluster into a string or crystal phase. We investigatethe phase behavior of cube-shaped colloidal particles in electric fields, using both Monte Carlosimulations and experiments. In addition to string fluid and orientationally ordered bct phases,we observe a columnar phase consisting of hexagonally ordered strings of rotationally disorderedcubes. By simulating the system for a range of pressures and electrical field strengths, we map outan approximate phase diagram, and compare the results to the structures seen in an experimentalsystem of sharp neighborite (NaMgF 3 ) colloidal cubes in an external field.[1] A. -P. Hynninen, M. Dijkstra, Phys. Rev. Lett. 94 138303 (2005).[2] F. Smallenburg, M. Dijkstra, J. Chem. Phys. 132, 204508 (2010).[3] M. E. Leunissen, H. R. Vutukuri, A. van Blaaderen, Adv. Mater. 21, 3116 (2009).155