Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 30, Issue 7, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201909537
Keywords
anisotropic deswelling; cholesteric liquid crystal elastomer; rubber; tunable structural color
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Funding
- European Research Council under the European Union [648763]
- Fonds National de la Recherche (FNR) [C17/MS/11703329/trendsetter]
- European Research Council (ERC) [648763] Funding Source: European Research Council (ERC)
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Cholesteric liquid crystal elastomers (CLCEs) are soft and dynamic photonic elements that couple the circularly polarized structural color from the cholesteric helix to the viscoelasticity of rubbers: the reflection color is mechanically tunable (mechanochromic response) over a broad range. This requires uniform helix orientation, previously realized by long-term centrifugation to ensure anisotropic deswelling, or using sacrificial substrates or external fields. The present paper presents a simple, reproducible, and scalable method to fabricate highly elastic, large-area, millimeters thick CLCE sheets with intense uniform reflection color that is repeatably, rapidly, and continuously tunable across the full visible spectrum by stretching or compressing. A precursor solution is poured onto a substrate and allowed to polymerize into a 3D network during solvent evaporation. Pinning to the substrate prevents in-plane shrinkage, thereby realizing anisotropic deswelling in an unprecedentedly simple manner. Quantitative stress-strain-reflection wavelength characterization reveals behavior in line with theoretical predictions: two linear regimes are identified for strains below and above the helix unwinding threshold, respectively. Up to a doubling of the sample length, the continuous color variation across the full visible spectrum repeatedly follows a volume conserving function of the strain, allowing the CLCE to be used as optical high-resolution strain sensor.
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