Multiresponsive Cylindrically Symmetric Cholesteric Liquid Crystal Elastomer Fibers Templated by Tubular Confinement

Abstract

Cylindrically symmetric cholesteric liquid crystal elastomer (CLCE) fibers templated by tubular confinement are reported, displaying mechanochromic, thermochromic, and thermomechanical responses. The synthesis inside a sacrificial tube secures radial orientation of the cholesteric helix, and the ground state retroreflection wavelength is easily tuned throughout the visible spectrum or into the near‐infrared by varying the concentration of a chiral dopant. The fibers display continuous, repeatable, and quantitatively predictable mechanochromic response, reaching a blue shift of more than −220 nm for 180% elongation. The cylindrical symmetry renders the response identical in all directions perpendicular to the fiber axis, making them exceptionally useful for monitoring complex strains, as demonstrated in revealing local strain during tying of different knots. The CLCE reflection color can be revealed with high contrast against any background by taking advantage of the circularly polarized reflection. Upon heating, the fibers respond—fully reversibly—with red shift and radial expansion/axial contraction. However, there is no transition to an isotropic state, confirming a largely forgotten theoretical prediction by de Gennes. These fibers and the easy way of making them may open new windows for large‐scale application in advanced wearable technology and beyond.

Bioinspired Stretchable Polymers for Dynamic Optical and Thermal Regulation

“…Geng et al developed a simple method for making long CLCE fibers that exhibit excellent mechanochromic response across the entire visible spectrum, upon elongational strain up to 200% (Figure 2b). [46,47] The CLCE fibers were sewn into clothes, which could withstand regular washing and repeated stretching. This fabrication method and the resulting CLCE fibers are appealing for applications in wearable technology and other fields benefiting from strong deformation detection or autonomous strain sensing.…”

Controlling the Optical Properties of Transparent Auxetic Liquid Crystal Elastomers

“…One of the earliest proposals of an optical device using LCEs was a contact lens concept by Amigó-Melchior et al, which used the optical anisotropy of a monodomain LCE to produce a bifocal lens suitable for treating conditions such as astigmatism and presbyopia . The refractive indices of LCEs are also critical to their sensitivity and appearance in optical strain sensing and mechanochromic devices which are based on the photoelastic (strain-induced birefringence) and selective reflection (strain-dependent chiral nematic pitch) effects. ,− More broadly, where an LCE is integrated into an optical or display device, for instance, for haptic, cleaning, or protection purposes, the material refractive indices and transparency will affect the optical quality of the whole device. The refractive indices of optical plastics are widely reported in the range of 10–40 °C to understand and optimize suitability for applications at near-ambient conditions .…”

Sticky Multicolor Mechanochromic Labels

“…Dynamic color control enables communication and interaction between living species in a diversity of biological and artificial environments. − This has been the inspiration for the development of mechanochromic materials whose structural color changes in response to mechanical stimuli. − Cholesteric liquid crystal elastomers (CLCEs) are prominent among such materials as the structural colors can be easily programmed. The colors arise from the helical twisting of anisotropic rod-shaped liquid crystal (LC) molecules along an axis perpendicular to the molecular director which in turn can be tuned by the concentration of the chiral dopant. − The programmable dynamic structural colors of CLCEs make them prominent candidates for information delivery. − However, the mechanochromic effect is usually manifested by translucent thin films, − thus integration with real-world applications is challenging. Moreover, mechanochromic materials are normally limited to uniform color-shifting which restrains their communication capabilities. − Visual information for ornamentation or functional purposes can be conveyed with sticky labels.…”