# Defect topologies in nematic liquid crystals

Martin Schoen
Technical University of Berlin
November 8, 2012
Duke University, Schiciano A | 4:30pm

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 $\widehat{\bm{n}}_{0}$.  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 {\em et al.}, Phys. Rev. E {\bf 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. We also observe two other novel defect topologies that have not been reported thus far either experimentally or theoretically.