Fabrication of Arrays of Topological Solitons in Patterned Chiral Liquid Crystals for Real‐Time Observation of Morphogenesis

Abstract

Topological solitons have knotted continuous field configurations embedded in a uniform background, and occur in cosmology, biology, and electromagnetism. However, real‐time observation of their morphogenesis and dynamics is still challenging because their size and timescale are enormously large or tiny. Liquid crystal (LC) structures are promising candidates for a model‐system to study the morphogenesis of topological solitons, enabling direct visualization due to the proper size and timescale. Here, a new way is found to rationalize the real‐time observation of the generation and transformation of topological solitons using cholesteric LCs confined in patterned substrates. The experimental demonstration shows the topologically protected structures arise via the transformation of topological defects. Numerical modeling based on minimization of free energy closely reconstructs the experimental findings. The fundamental insights obtained from the direct observations pose new theoretical challenges in understanding the morphogenesis of different types of topological solitons within a broad range of scales.

Planar Spin Glass with Topologically Protected Mazes in the Liquid Crystal Targeting for Reconfigurable Micro Security Media

“…Typically, topological soliton formed in the chiral LCs is knotted LC director (nˆ) field configurations embedded in uniformly aligned LCs, where nˆindicates the longitudinal axis of rod-like LC molecules. [23][24][25][26][27][28][29][30] The behavior of this topological soliton of LCs is similar to that of a solitary wave in nature, known as a soliton, and it does not break apart without external stimuli above its stabilization energy barrier. Among various topological solitons in the chiral LCs, cholesteric fingers (CFs), including CF-1, CF-2, and CF-3, can serve as the 1D topological solitons.…”

“…A spatial gradient of capillary force is induced by the square hole-array pattern, which subsequently leads to the air cavities (pattern region where the LCs are not filled in). [30,35,36] When the temperature steadily decreases to 30 °C at a rate of −1 °C min −1 , the difference in heat capacity between air and LC induces a directional thermal phase transition from the air surfaces (Figure 2a and Video S1, Supporting Information). As the sample is cooled further, the cholesteric regions expand in a radial direction outward from the air surfaces.…”

“…CF-3s are made up of nˆfield configurations that 𝜋 rotate in a given direction (i.e., x-axis), and their twist terminates in two disclination lines (black circles, along the y-axis) near the upper and lower confining substrates (Figures 1e and 3b). [29,30] These disclination lines are regions with the pseudo-isotropic phase, inducing unpredictable optical scattering because of the differences in the refractive indices surrounding the LCs. [37] The consequence of the complicated scattering is perceived as dark lines in the outof-focus optical microscope image (marked with green arrows in Figure 3c).…”

“…Our security system can adopt other topologically protected structures, such as torons, categorized as a 2D topological soliton. [26,27,30] Reducing the LC cell gap from ≈5 to ≈4 μm enables the generation of the torons, allowing the assignment of binary values based on the presence or absence of torons. These topological solitons, being generated unpredictably, make arbitrary arrangements suitable for use as binary-based optical PUFs similar to a CF-3based maze.…”

Recent Progress in Functional Dye‐Doped Liquid Crystal Devices

“…[54c,103] Ch-LCs exhibit a helical LC organization, in which successive layers of nematic LCs are displaced by a small rotation in molecular direction concerning their neighboring layers. [22,104] Owing to their helical superstructures, the Ch-LCs with planar textures present Bragg reflection and show structure colors when their reflection wavelengths are centered at the visible region. [105] The structure colors of Ch-LCs can be regulated by many stimuli, resulting in various color images.…”