Excellent performance of pH sensitive artificial muscles under large loading

The pH-responsive artificial muscle is a chemical-driven actuator without external power input. However, the low work density and adequate stability limit their practical applications. Herein, we combine the porous pHresponsive polymer with carbon fiber bundles for obtaining the coiled hybrid fiber. The coiled carbon fiber (CNF) yarn enhances the strength of hybrid fiber, and the swelling pH sensitive polymer limited to CNF provide a large stroke for hybrid fiber untwisting, resulting in an excellent work capacity and a high cycle life. When the load weight is 600 times the weight of the fiber itself, its work density reaches 287 kJ/m3. In addition, the hybrid fiber can reach a maximum stretching and contraction of 47% at a load of 400 times its own weight. The breaking stress of the obtained artificial muscle can reach more than 100 MPa. At the same time, the constructed porous polymer hydrogels improve the response rate of the artificial muscle, the response time is shortened to 10 min and do not decay in hundreds of cycles, which is further shown that the limiting effect of carbon fiber on the polymer improve the stability of the artificial muscle. It is indicated that the pH-responsive composite fibers have a high potential for use in artificial muscles, pH sensors and mechanical system.