Slidable Cross-Linking Effect on Liquid Crystal Elastomers: Enhancement of Toughness, Shape-Memory, and Self-Healing Properties

The network structures of liquid crystal elastomers (LCEs) are crucial to impart rubbery behavior to LCEs and enable reversible actuation. Most LCEs developed to date are covalently linked, implying that the cross-links are fixed at a particular position. Herein, we report a new class of LCEs integrating polyrotaxanes (PRs) as slidable cross-links (PR-LCEs). Interestingly, the incorporation of a low loading (0.3-2.0 wt %) of the PR cross-linkers to the LCE causes a significant impact on various properties of the resulting PR-LCEs due to the pulley effect. The optimum PR loading is determined to be 0.5 wt %, at which point the toughness and damping behavior are maximized. The robust mechanical properties of the PR-LCE offers a superior actuation performance to that of the pristine LCE along with an excellent quadruple shape-memory effect. Furthermore, the incorporation of PR is useful to enhance the efficiency of shape-memory-assisted self-healing when heating above the nematic-isotropic transition.