Defect topologies in a nematic liquid crystal near a patchy colloid

Using isothermal-isobaric Monte Carlo simulations we investigate defect topologies 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 \documentclass[12pt]{minimal}\begin{document}$\widehat{\bm {n}}_{0}$\end{document} n ̂ 0 . Considering a chemically homogeneous colloid as a special case we observe the well-known surface and saturn ring defect topologies for weak and strong perpendicular anchoring, respectively; for homogeneous, strong parallel anchoring we find a boojum defect topology that has been seen experimentally [see P. Poulin and D. A. Weitz , Phys. Rev. E 57 , 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 defect topology in agreement with recent experimental studies [see M. Conradi , M. Ravnik , M. Bele , M. Zorko , S. Žumer , and I. Muševič , Soft Matter 5 , 3905 ( 2009 )] . We also observe two other novel defect topologies that have not been reported thus far neither experimentally nor theoretically.