Stabilized director buckling patterns in nematic elastomers and their dynamic optical effects

Abstract

Abstract: Pearlescence and iridescence, which are a class of light diffusion effects that exhibit sharp viewing-angle-dependent brightness and colors, are important material properties for notification purposes and lighting devices. Here we report elastomeric materials with self-organized periodic birefringent patterns that exhibit these optical effects, with additional dynamic and reversible tunability. A stack of micron-thick layers, each of which has a nematic director tilted from the layer normal in a different direction, assembles a birefringence-pattern-based anisotropic diffuser in a nematic liquid-crystal elastomer. The periodic pattern is formed after buckling induced by the uniaxial thermal shrinkage, and the associated rotation of an initially uniform director state. The patterns can be stabilized by secondary crosslinking. Upon deformation or increasing the temperature, the light diffusion with viewing-angle-dependent colors reversibly fades owing to the diminishing of optical effects via strain-induced alignment or thermal randomization of birefringence, respectively. Such elastomers with tunable self-organized birefringence patterns can be used for reconfigurable optical elements and strain/temperature detection in the form of films, tapes, rods, and fibers.