The Effect Of Spherical Surface On The Deformation Of +1 Boojum Defect

Based on the Landau-de Gennes theory,using the relaxation iterative method,a cylinder-inscribed-sphere nematic liquid crystal(NLC)system with+1 boojum was established.Structural transition of+1 boojum defect induced by anchoring conditions on the spherical interface was firstly studied.Then,by comparing with the structural transition process of+1 boojum in the cylinder system,we focused on the effect of spherical surface on the deformation of boojum.Firstly,we studied a cylinder-inscribed-sphere NLC system with+1 boojum.Strong anchoring conditions was set both on spherical surface and lower substrate,LC molecules were aligned along the spherical surface and perpendicular on the lower substrate.Results showed that a+1 boojum and a defect ring appeared when increasing the radius of the cell.With the radius continue to increase,biaxiality of defect ring increased and gradually spread along the sphere.Secondly,a cylindrical NLC system with a+1 boojum was studied.The thickness of system is h,radius is R,and strong tangential anchoring were imposed on both substrates.With the increasing of the radius,order reconstruction(OR)gradually disappeared instead of one boojum and induced a defect ring.When reached the critical thickness_ch=10ξ(ξis the coherence length),new OR induced by defect ring appeared.Thirdly,in the cylinder-inscribed-sphere NLC cell,a fingerless boojum was appeared at the center of the spherical surface with a small radius(r≈10ξ)when the upper substrate was weak anchoring boundary condition,and the lower substrate anchoring condition remains unchanged.However,there is no new structural transition occurred in the cylindrical NLC cell.Finally,by compared+1 boojum defect structure between two models under different anchoring conditions,it’s found that the structural transition process of+1 boojum defect under strong or weak anchoring conditions were basically the same,but there were some slight differences.