Cholesteric Liquid Crystal Shells as Enabling Material for Information‐Rich Design and Architecture

Abstract

The responsive and dynamic character of liquid crystals (LCs), arising from their ability to self-organize into long-range ordered structures while maintaining fluidity, has given them a role as key enabling materials in the information technology that surrounds us today. Ongoing research hints at future LC-based technologies of entirely different types, for instance by taking advantage of the peculiar behavior of cholesteric liquid crystals (CLCs) subject to curvature. Spherical shells of CLC reflect light omnidirectionally with specific polarization and wavelength, tunable from the UV to the infrared (IR) range, with complex patterns arising when many of them are brought together. Here, these properties are analyzed and explained, and future application opportunities from an interdisciplinary standpoint are discussed. By incorporating arrangements of CLC shells in smart facades or vehicle coatings, or in objects of high value subject to counterfeiting, game-changing future uses might arise in fields spanning information security, design, and architecture. The focus here is on the challenges of a digitized and information-rich future society where humans increasingly rely on technology and share their space with autonomous vehicles, drones, and robots.

Facile Anisotropic Deswelling Method for Realizing Large‐Area Cholesteric Liquid Crystal Elastomers with Uniform Structural Color and Broad‐Range Mechanochromic Response

“…As color is one of the most natural indicators seen by the naked eye, the mechanochromic response of CLCEs is attractive far beyond lasing. CLCEs could enable tensile and/or pressure sensors capable of visualizing mechanical strain in many objects of significant societal, technical, and/or commercial importance, such as clothing, packaging, pressurized vessels or in various architectural features . Picot et al demonstrated such a strain sensor operating in real‐time, albeit with an optical response range no greater than ≈40 nm (from orange to green); this limitation can be traced back to the bilayer nature of the sensor, the cholesteric being supported on a nylon substrate that restrains the overall elasticity.…”

Structural Color Materials for Optical Anticounterfeiting

“…Reproduced with permission. [ 38 ] Copyright 2018, Wiley‐VCH. d) The optical signature of planar‐aligned ChLC shells and the schematic drawing of the reflection behavior.…”

“…The intrinsically random textures of the cholesteric phase, generated from nonequilibrium states of the liquid crystals under quick solidifying, have been used for unpredictable identifier tags for enhanced security. [ 38 ] The great diversity of optical features enable physically unique and unclonable encryption means. Moreover, various optical images could be generated from a single cholesteric liquid crystal.…”

“…As demonstrated by Schwartz et al, a cholesteric liquid crystal shell showed continuously shifting images by turning the illumination area (Figure 5c‐i,ii), focus (Figure 5c‐iii,iv) and observation modes with crossed polarizers (Figure 5c‐v) or a λ∕4 phase plate (Figure 5c‐vi). [ 38 ] In addition to random textures, the cholesteric shells in a hollow microfluidic sphere enable a sequence of internal reflections, as demonstrated by Lagerwall and co‐workers. [ 39 ] Asymmetric cholesteric shells that were thick on top appeared as colored spots, while asymmetric cholesteric shells that were thin on top generated additional concentric colored rings (Figure 5d), as a result of a sequence of internal reflections inside the hollow sphere.…”

“…In addition, the stability of the structural color and the robustness of the structural color anticounterfeiting materials can benefit from further development of self‐reinforced structural color systems, [ 19 ] and optical/mechanical self‐healable systems. [ 158–160 ] On the other hand, despite some previous works that referred to unclonable patterns based on structural color materials, [ 38,71,157,161 ] it is still a great challenge to achieve a cost‐effective structural color tag generated through a stochastic process. Such highly secure anticounterfeiting systems can essentially make counterfeiting impossible.…”