Stiffness Variable Polymer for Soft Actuators with Sharp Stiffness Switch and Fast Response

Stiffnessvariable polymers are an essential family of materialsthat have aroused considerable attention in soft actuators. Althoughlots of strategies have been proposed to achieve variable stiffness,it remains a formidable challenge to achieve a polymer with a widestiffness range and fast stiffness change. Herein, a series of variablestiffness polymers with a fast stiffness change and wide stiffnessrange were successfully synthesized, and the formulas were optimizedvia Pearson correlation tests. The rigid/soft stiffness ratio of thedesigned polymer samples can reach up to 1376-folds. Impressively,owing to the phase-changing side chains, the narrow endothermic peakcan be observed with full width at half-maximum within 5 degrees C.Moreover, the shape memory properties of the shape fixity (R (f)) and shape recovery ratio (R (r)) values of the shape memory properties could reach upto 99.3 and 99.2%, respectively. Then, the obtained polymer was introducedinto a kind of designed 3D printing soft actuator. The soft actuatorcan achieve sharp heating-cooling cycle of 19 s under a 1.2A current with 4 degrees C water as coolant and can lift a 200 g weightat the actuating state. Moreover, the stiffness of the soft actuatorcan reach up to 718 mN/mm. The soft actuator exhibits an outstandingactuate behavior and stiffness switchable capability. We expect ourdesign strategy and obtained variable stiffness polymers to be potentiallyapplied in soft actuators and other devices.