Fine structure of defects in radial nematic droplets

We investigate the structure of defects in nematic liquid crystals confined in spherical droplets and subject to radial strong anchoring. Equilibrium configurations of the order-parameter tensor field in a Landau-de Gennes free energy are numerically modeled using a finite-element package. Within the class of axially symmetric fields, we find three distinct solutions: the familiar radial hedgehog, the small ring (or loop) disclination predicted by Penzenstadler and Trebin, and a solution that consists of a short disclination line segment along the rotational symmetry axis terminating in isotropic end points. Phase and bifurcation diagrams are constructed to illustrate how the three competing configurations are related. They confirm that the transition from the hedgehog to the ring structure is first order. The third configuration is metastable (in our symmetry class) and forms an alternate solution branch bifurcating off the radial hedgehog branch at the temperature below which the hedgehog ceases to be metastable. Dependence on temperature, droplet size, and elastic constants is investigated, and comparisons with other studies are made.