Creating arbitrary arrays of two-dimensional topological defects

Abstract

An atomic force microscope was used to scribe a polyimide-coated substrate with complex patterns that serve as an alignment template for a nematic liquid crystal. By employing a sufficiently large density of scribe lines, two-dimensional topological defect arrays of arbitrary defect strength were patterned on the substrate. When used as the master surface of a liquid crystal cell, in which the opposing slave surface is treated for planar degenerate alignment, the liquid crystal adopts the pattern's alignment with a disclination line emanating at the defect core on one surface and terminating at the other surface.

Decomposition vs. escape of topological defects in a nematic liquid crystal

“…1) was patterned onto a thin layer of polyvinyl alcohol (PVA) that had been deposited onto an indium-tin-oxide (ITO)-coated glass substrate, a method similar to that described in detail in Ref. 5. [We note that in our previous work 5,6 we had used the polyamic acid RN-1175 (Nissan Chemical Industries).]…”

“…Our group recently developed the method of scribing a polymer-coated substrate using an atomic force microscope (AFM) stylus to create planar TD patterns on similar length scales, including arrays of line TDs that have high defect "strength" m [Refs. 5,6]. Here m is defined as Δθ/2π, where θ is the nematic director's azimuthal angle with respect to an arbitrary axis and Δθ the director's total angular change on circumnavigating the defect line.…”

“…Topological defects entail a strain energy cost, which can be relaxed by several mechanisms, including decomposition of an integer defect into pairs of half-integer defects 5 or by escape of the director into the third dimension 7,8 . In a theoretical study, Chiccoli 9 , et al estimated the free energy of a pair of strongly anchored (split) half-integer defects to be , where K is an elastic constant; d is the cell thickness; R is a characteristic domain size, e.g., the spacing between our patterned integer defects; L is the gap separating the split defects; r is a molecular size; and u is the normalized defect core energy.…”

Designs of Plasmonic Metamasks for Photopatterning Molecular Orientations in Liquid Crystals

“…Complex periodic patterns of molecular orientations can also be obtained through photoalignments by using interference of laser beams [23,24]. Another development is to use curvilinear nanogrooves generated on polyimide films by tips of an atomic force microscope [25]. Recent studies have also extended the photoalignment techniques to lyotropic LC systems [19,26].…”

Bistable director alignments of nematic liquid crystals confined in frustrated substrates

“…With them, many types of structured surfaces for the liquid crystals and the resulting director alignments have been reported in the past few decades [9,11,23,[28][29][30][31]. For example, a striped surface, in which the homeotropic and planar anchorings appear alternatively, was used to control the polar angle of the director field in the bulk [32][33][34].…”