Mechanically robust liquid crystal elastomer actuator using combined covalent and topological sliding-ring crosslinking

Liquid crystal elastomers (LCEs) have attracted considerable interest due to their ability to undergo reversible actuation with large deformation, positioning them among the most promising materials for soft actuators and robotics. Traditional LCE actuators rely on using covalent or dynamic covalent chain crosslinking to fix the alignment of mesogens required for reversible deformation. In this study, we introduce cyclodextrin (CD)-based polyrotaxane (PR) topological crosslinkers in a covalently crosslinked LCE actuator to enhance its mechanical properties without compromising its actuation performance, which is beneficial for applications where the actuator is subjected to large and repeated deformations. We show that the incorporation of a small amount of PR crosslinkers, which allow for energy dissipation through CD ring sliding, can maintain the reversible actuation capabilities of the LCE actuator and, in the same time, improve significantly its fracture toughness, fatigue resistance and tear resistance. The demonstrated approach of combining a primary covalent crosslinking for actuation and a secondary topological crosslinking for energy dissipation, resulting in synergetic enhancement of mechanical properties and retention of actuation performance, opens new avenues for the development of LCE actuators for applications requiring both superior actuation and mechanical properties.