Transformation from walls to disclination lines: Statics and dynamics of the pincement transition

Abstract

We present an experimental and theoretical study of the pincement phenomenon-transformation of a wall associated with the Fréedericksz transition into a pair of disclination lines. We measure the velocity of the boundary (front) between the two states as a function of the voltage. Experimental results are recovered by numerical simulations based on the nematic tensor order parameter, which also reveal the detailed three-dimensional structure of the front. By introducing reduced models we obtain approximate expressions for the two-state coexistence voltage and the front velocity. We find a bifurcation scenario incorporating a pair of saddle nodes at which the wall and disclination solutions appear or disappear.

Three-dimensional positioning and control of colloidal objects utilizing engineered liquid crystalline defect networks

“…On further increasing the voltage, it is found that the walls undergo a ‘pincement' transition, in which a wall separates into two disclinations bound to each substrate confining the liquid crystal 31 and extends outside the boundary of the alignment pattern ( Supplementary Movie 3 ). The attraction of the particles to the top and bottom substrates observed in Fig.…”

Nematic Liquid Crystals Confined Within a Microfluidic Device: Static Case

“…The implications of twist domains on the overall director field is far from trivial. The free energy minimization of the twist walls proceeds via complicated steps, generally setting off a cascade of defect dynamics: transformation of the wall to line defects (pincement) [7], and the interactions between the bulk and the surface disclination lines [8][9][10]. The formation of the twist or planarly aligned domains occurs at the phase transition of 5CB from isotropic to nematic phase.…”

Hydrodynamics of fringing-field induced defects in nematic liquid crystals

“…Disclinations can be of high density, playing an important and potentially advantageous role in device operation. Such fringing-field induced disclinations are the product of pincement, an effect which is well studied in liquid crystal cells with planar alignment [4][5][6][7][8] or in multi-domain structures 9 . For very high resolutions, pixels become narrow compared to the cell gap, which is fixed by the optical path length.…”