Directed Self-Assembly of Topological Defects of Liquid Crystals

Abstract

One of the alluring aspects of liquid crystals (LCs) is their readily controllable self-assembly behavior, leading to comprehension of complex topological structures and practical patterning applications. Here, we report on manipulating various kinds of topological defects by adopting an imprinted polymer-based soft microchannel that simultaneously imposes adjustable surface anchoring, confinement, and uniaxial alignment. Distinctive molecular orientation could be achieved by varying the surface anchoring conditions at the sidewall polymer and the rubbing directions on the bottom layer. On this pioneering platform, a common LC material, 8CB (4'-n-octyl-4-cyano-biphenyl), was placed where various topological defect domains were generated in a periodic arrangement. The experimental results showed that our platform can change the packing behavior and even the shape of topological defects by varying the rubbing condition. We believe that this facile tool to modulate surface boundary conditions combined with topographic confinement can open a way to use LC materials in potential optical and patterning applications.

Role of Stimuli on Liquid Crystalline Defects: From Defect Engineering to Switchable Functional Materials

“…Polymers having either LC molecular-philic or -phobic properties are put on a substrate by the spin-coating method. Frequently encountered polymeric materials are polyimide (PI) [33], polyethyleneimine (PEI) [34], and polyvinyl alcohol (PVA) [35]. Some reported methods for surface treatment involve self-assembled monolayers (SAMs) [36,37].…”

“…Since Choi et al [50] reported the exploitation of microchannels to generate periodic smectic defects, many experimental results using microchannels have been obtained [17,28,33,34,[51][52][53][54][55]. As LC materials should adopt a specifically defined orientation under limited volume and surface conditions of microchannels, the so-called confinement effect, they develop a peculiar structure in a periodic manner.…”

Light‐Activated Liquid Crystalline Hierarchical Architecture Toward Photonics

“…In addition to the 3D topographic confinement, the internal surface alignment of the microchannels and the SLC molecular structure were also key parameters that would determine the long‐range‐ordered TFCD array. For example, Shin et al produced various periodic arrays of topological defects, including tilted FCDs with nonzero eccentricities and zigzag patterns by presetting anchoring conditions of the microchannels . And, SLC materials with fluorinated moieties would facilitate the generation of highly ordered TFCD arrays compared to those with alkyl chains.…”

Reconfigurable Periodic Liquid Crystal Defect Array via Modulation of Electric Field

“…One of the most interesting fields in LC science and engineering is the fabrication of periodic topological defect domains for use in optical vortex generators, grating devices, lithographic templates, and as scaffolds for arrayed colloids . To realize these numerous systems, various kinds of platforms have been suggested, which include the use of topographical confinement, mechanical rubbing, epitaxial growth, chemical treatments, ionic effects, and external fields such as electric and magnetic fields …”

“…Among the various LC phases, the LC structures formed in the smectic phase have been considered the most efficient and robust medium to generate distinct topological defect structures . However, there are still challenges to exploit smectic structures because they are extremely hard to be aligned or oriented uniformly over a large area, due to their short‐range order characteristics and high viscosity.…”