Polydopamine coated MXene and cellulose nanocrystal as photothermal and reinforcing nanofiller for liquid crystal...

Liquid crystal elastomer (LCE) is promising as soft actuator due to its rubbery elasticity and thermal actuating properties. However, precise thermal control is challenging and LCE suffers from insufficient mechanical strength and poor photothermal performance, which limits its wide applications in soft robotics. In this study, polydopamine (PDA) coated MXene and cellulose nanocrystal (CNC) nanocomposite (PMC) was developed as an efficient photothermal and reinforcing nanofiller to endow LCE with precise light actuating function and enhanced mechanical properties. MXene was employed as photothermal nanofiller due to its outstanding photothermal conversion efficiency; PDA formed by oxidization self-polymerization of dopamine was used to enhance antioxidation stability of MXene and miscibility between MXene and LCE; CNC was employed as dispersant to prevent aggregation of MXene during PDA coating and reinforcing nanofiller. The obtained PMC incorporated LCE (PMC-LCE) displayed excellent photothermal ability (reaching 200 ℃ in 20 s), significant enhanced mechanical properties (Young's modulus 5.0 MPa, tensile stress 20.6 MPa, and elongation at break of 132.8 %), and was able to lift a load of 100 g (1500 times of its own weight) with work density of 89.2 kJ m^-3 (twice of mammal skeletal muscle). A variety of PMC-LCE based soft actuators with programmable deformations and movements were obtained via precise NIR control, sticking tape, shape tailoring, and LC alignment design, and could realize a variety of functionalities, such as clamping, walking, rotating, and swimming. This study facilitated LCE based soft actuator and MXene/CNC based photothermal and reinforcing nanofiller for many promising applications.