Artificial web of disclination lines in nematic liquid crystals

Mengfei Wang,Yannian Li,Hiroshi Yokoyama

doi:10.1038/s41467-017-00548-x

Mengfei Wang, Yannian Li + Show 1 more

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https://doi.org/10.1038/s41467-017-00548-x

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Abstract

Disclinations are topological singularities of molecular arrangement in liquid crystals, which typically occur when the average orientation of molecules makes a π rotation along a fictitious closed loop taken inside the liquid crystal. Depending on the sense of molecular rotation, the disclination lines are either of 1/2 or −1/2 strength. When two disclination lines with the opposite strength meet, they are annihilated without trace. It is hence generally considered difficult in the nematic phase to stabilize a condensed array of free-standing disclination lines without the aid of topological objects like colloidal inclusions. Here we show that a free-standing web of 1/2-strength twist disclination lines can be stably formed in thin liquid crystal cells by means of a judicious combination of orientationally patterned confining surfaces fabricated by the micropatterned photoalignment technique. Theoretical model indicates that disclination lines are held apart at the intersection by a repulsive force generated by the Frank elasticity.

Highlights

Disclinations are topological singularities of molecular arrangement in liquid crystals, which typically occur when the average orientation of molecules makes a π rotation along a fictitious closed loop taken inside the liquid crystal
We present the theoretical expressions of the forces in play in this system, followed by the experimental demonstration that a freestanding web of 1/2-strength disclination lines can be stably formed in thin liquid crystals (LCs) cells through a proper combination of orientationally patterned confining surfaces
The LC tries to resolve the structural incompatibility by periodically introducing a 1/2-strength twist disclination line for every π rotation of the director, which leads to the generation of an array of closed disclination loops concentric with the surface pattern with small rounding at the corner (Fig. 1b–d), which is caused by the balance between the line tension of the disclination and the elastic stress generated by the imbalance of the twist deformations across the disclination line

Summary

Introduction

Disclinations are topological singularities of molecular arrangement in liquid crystals, which typically occur when the average orientation of molecules makes a π rotation along a fictitious closed loop taken inside the liquid crystal. Depending on the sense of rotation of the director along the loop, there arise two subtypes referred to as 1/2 and −1/2-strength disclinations, they are not topologically distinct[3] This type of disclination lines are densely formed at the phase transition, when the isotropic liquid is suddenly cooled down to the nematic phase, because of the nucleation of numerous nematic LC domains with random director orientations. There have been attempts for artificial manipulation of disclination lines by means of topologically conflicted boundaries[5,6,7] and by use of topological objects like colloidal inclusions[8, 9] Their inherent readiness for annihilation has hampered the realization of condensed array of free-standing disclination lines in nematic LCs as those involving line intersectoins. According to the theoretical estimates of the forces acting between disclination lines and a z y c b d

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