Defect topologies in a nematic liquid crystal near a patchy colloid

Using isothermal-isobaric Monte Carlo simulations we investigate defecttopologies due to a spherical colloidal particle immersed in a nematic liquid crystal.Defects arise because of the competition between the preferential orientation at the colloid's surface and the far-field director nˆ0. Considering a chemically homogeneous colloid as a special case we observe the well-known surface and saturn ring defecttopologies for weak and strong perpendicular anchoring, respectively; for homogeneous, strong parallel anchoring we find a boojum defecttopology that has been seen experimentally [see P. Poulin and D. A. Weitz, Phys. Rev. E57, 626 (1998)] but not in computer simulations. We also consider a heterogeneous, patchy colloid where the liquid-crystal molecules anchor either preferentially planar or perpendicular at the surface of the colloid. For a patchy colloid we observe a boojum ring defecttopology in agreement with recent experimental studies [see M. Conradi, M. Ravnik, M. Bele, M. Zorko, S. Žumer, and I. Muševič, Soft Matter5, 3905 (2009)]. We also observe two other novel defecttopologies that have not been reported thus far neither experimentally nor theoretically