Stress-Director Coupling in Patterned Monodomain-Polydomain Liquid Crystal Elastomers

Background Liquid crystal elastomers (LCEs) exhibit unique mechanical properties derived from its coupled rod-like liquid crystals (LCs) and polymer chains. They are promising materials in many applications such as artificial muscle, soft robotics, and energy dissipation devices. However, a clear understanding of the stress-director coupling mechanism across different patterned LCEs remain limited. Objectives This work patterns LCEs with both monodomain and polydomain regions to create monodomain-polydomain (MP) LCEs and illustrate the stress-director coupling associated with various patterns. Methods Using two-stage thiol-acrylate Michael addition photopolymerization (TAMAP) reaction, we fabricate MP LCEs through sequentially curing selected regions with or without pre-stretching. We then apply uniaxial loading to different MP LCEs and characterize the strain distribution and director reorientation both experimentally and computationally. Results By changing the director angle in monodomain regions and the geometry of polydomain regions, we modulate the shear compliance and relative stiffness between monodomain and polydomain regions. As a result, we demonstrate the distinct deformation in various MP LCE patterns and reveal the driving mechanism derived from the interplay between stress-director coupling and geometric constraints. Conclusion In conclusion, this study presents thorough understanding about the stress-director coupling effect on the deformation of MP LCEs and provides design guidelines for patterned LCEs.