Coupling between Fingerprint Texture Evolution and Mechanical Anisotropy in Lying-Helix Cholesteric Liquid Crystal Elastomers

We investigate the nonlinear mechanical response of main-chain cholesteric liquid crystal elastomer films with a lying-helix director configuration (LH-CE), in which the helical axis lies within the film plane. The fingerprint (FP) texture intrinsic to the LH configuration exhibits a dichotomous response to uniaxial stretching depending on the angle (θ 0 ) between the initial stripe orientation and the stretching direction. Stripe domains with |θ 0 | ≪ 90°, which constitute the vast majority of the system, rotate toward the stretching axis while largely preserving their spacing, thereby governing the macroscopic mechanical properties. In contrast, for the minority domains with |θ 0 | ≈ 90°, the stripe spacing increases with strain under minimal rotation. Stripe realignment within the film plane produces pronounced anisotropy in macroscopic contraction dominated by width contraction and generates a stress plateau. Subsequent stretching induces untwisting of the helical structure, leading to a steep stress upturn accompanied by strongly anisotropic deformation dominated by thickness contraction. These findings reveal deformation-driven structural evolution of FP textures and provide a basis for mechanically controlling their associated mechano-optical responses.