Polyaniline-Incorporated Liquid Crystal Elastomers for Muscle-like Actuation

Rapid developments in machine intelligence and human–machine interactions have opened widespread interest in artificial muscles owing to their huge application potential in soft robotics and biomedical fields. In this work, liquid crystal elastomer (LCE) and polyaniline (PANI)-doped LCE composite films were described, and their muscle-like actuation along with weight-lifting capabilities has been demonstrated. The composite films were prepared by doping 0.04, 0.08, 0.12, 0.16, and 0.24 wt % of PANI through a thiol-ene Michael addition reaction. Generally, LCEs show actuation in response to heat, at mesophase to isotropic transition, due to a change in the order of the system. PANI is employed to utilize light, infrared radiation (IR) in particular, to drive the actuation considering PANI’s excellent photothermal properties. All the films displayed liquid crystal properties, and the addition of PANI did not influence the transition temperatures much. The mechanical properties of the films were well above the standards (stress is >0.35 MPa and strain is >40%) required for artificial skeletal muscles. Among the composite films, LCE/PANI-2 showed good stiffness (stress: 1.63 MPa; Young’s modulus: 3.056 MPa) with high tensile strength. All the elastomer films exhibited remarkable thermal actuation, photoactuation, and incredible weight-lifting properties. Photoactuation was studied by using an IR diode laser source (808 nm, 2 W). The films showed response instantaneously, within 3–4 s of photoirradiation, in terms of longitudinal contraction, accompanied by lateral widening, and the response was reversible. During the contraction, the films were able to lift weight. A better performance was recorded for the LCE/PANI-2 film (0.08 wt % PANI) that lifted a weight of 120 g, which is 1538 times its own weight, when exposed to IR diode laser light. Our results strongly pointed the suitability and potential of the prepared films for application as artificial muscles.