Low melting point alloy modified polymer composite with sharp stiffness switch for soft actuator

Materials possessing switchable stiffness, particularly dynamically switchable stiffness, have generated a lot of attention in the soft actuator. Herein, we proposed a facial poly (vinyl alcohol) (PVA) coating method to fabricate the micron-sized Field's metal (FM) phase-changing particles with an average particle size of about 1.2 μm, and obtained a series of stiffness variable polymer composites via incorporating FM particles into the designed stiffness variable polymer matrix. Owing to the rapid solid-liquid change and ultra-high modulus of FM, the rigid/soft stiffness ratio of the composites improved to 1442-folds. Moreover, the shape fixity (Rf) and shape recovery ratio (Rr) values of the shape memory properties could reach up to ultra-high values of 99.4% and 99.6%, respectively. Subsequently, the prepared composites were selected and used a 3D printing soft actuator as the stiffness variable units. The soft actuator exhibits short heating-cooling time of 36s under 1.2A current and with 4 °C water as the coolant, and it is able to lift a 200 g weight at the rigid state. Furthermore, the stiffness of obtained actuator can achieve high value 779 mN/mm. The results indicate that the obtained soft actuator possesses excellent actuate behavior and stiffness switchable ability. This work might provide faster and more rigid variable stiffness materials for soft actuators application in the real world. [Display omitted] •The micron-sized Field's metal particles with an average particle size of about 1.2 μm were synthetized by a facial method.•The stiffness variable composite with fast stiffness change and wide stiffness range were successfully synthesized.•The stiffness variable polymer achieve high rigid/soft stiffness ratio up to 1442-folds.•A kind of designed 3D printing soft actuator using obtained stiffness switchable composite as stiffness switch unit was fabricated.•The soft actuator can exhibit a fast heating-cooling cycle of 36s and outstanding load capability.