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Molecular simulations elucidate soft elasticity in polydomain liquid crystal elastomers Skacej, Gregor


Liquid crystal elastomers (LCE) — polymer networks with embedded liquid crystal units — are functional materials characterized by a pronounced coupling between elastic strain and liquid crystalline orientational ordering. When prepared by polymerization and cross-linking in the isotropic phase, and then cooled, the resulting polydomain ma- terials exhibit an extraordinary soft elastic behavior under unidirectional pulling, with a plateau-like region in the stress-strain curve, before turning into a monodomain LCE where a standard elastic resistance is recovered. Here we investigate the microscopic origin of this behavior by performing large-scale molecular iso-stress Monte Carlo simula- tions of swollen polydomain main-chain LCE. Our simulations are based on the soft-core Gay-Berne interaction potential and reproduce the stress-strain experiment featuring the plateau-like behavior. Deeper insight into the molecular organization of our sim- ulated samples reveals that the underlying mechanisms are local domain rotation and growth, excluding orientational order destruction-reconstruction. It also suggests that these mechanisms may be assisted by a dissipation of elastic free energy stored in topo- logical defects created during the synthesis, which is compatible with the stress-strain irreversibility observed in some main-chain LCE

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