Theoretical Study Of Curvature Induced Surface-order Reconstruction On The Generalized Nematic Liquid Crystal π Cell

In order to understand the effect of flexible substrates on display mode and performance,planar π cell and coaxial cylinder π cell were established.Nematic liquid crystal appeared splay state under the ground state（off-state）and bend state（on-state）when applied electric field within two models.Between on and off state,there exists a topological discontinuous transformation of LC directors n and the Hs state（symmetric splay state）can transformed into bend state through order reconstruction（OR）under high voltage.However,Frank elastic theory cannot have a precise explanation on OR phenomenon.Thus,Landau-de Gennes theory was used to study the structural transition of the system with both symmetric and asymmetric boundary conditions in the π cell.The influences about finite curvature radius and pretilt angle on OR can be studied by time-dynamics process of OR.Firstly,symmetric boundary conditions were set,i.e.pretilt angle of the upper（outer）and lower（inner）plates were-10° and 10° respectively in both models.In the coaxial cylinder π cell,Ha state（asymmetric splay state）appeared when U=35 due to the effect of the curvature.When （?）=40,Hs state appeared.With the threshold voltages about （?）_1th=42.3 and （?）_2th=42 respectively in the planar π and coaxial cylinde π cells,bend states were the only state in both models.Under the threshold voltage,according to the time-dynamics processes,when bend deformation completed in the coaxial cylinde π cell that the range of director with polar angle 180° will move towards the inner boundary compared to plana π cell due to the existence of curvature.Secondly,asymmetric boundary conditions were set,i.e.pretilt angle of plana π cell were set-200 on the upper and 1° on the lower plates and bulk OR appeared when the （?）_1th=73.In coaxial cylinder cell,pretilt angles were set 1°（20°）on the inner and-20°（-1°）on the outer surfaces.Surface OR appeared due to the finite curvature radius with the threshold voltage （?）_2th=63 and （?）_3th=78 in two ways,respectively.The relationship of the threshold voltage among three cases was （?）_th3>（?）_th1>（?）_th2.By varying the setting of pretilt angle and comparing the results among different models,we found that the larger the curvature was,the closer between OR and boundary.