Reversible Torsional Actuation of Hydrogel Filled Multifilament Fibre Actuator

Twisted polymer fibre actuators provide high torsional rotation from stimulated volume expansion, induced either by chemical fuelling, thermal stimulation, or electrochemical charging. One key limitation of these actuators is the irreversibility of torsional stroke that limits their feasibility when considering real-life smart applications. Moreover, scaling the torsional stroke of these actuators becomes difficult when these are integrated into practically usable systems such as smart textiles, due to the external and variable opposing torque that is applied by the adjacent non-actuating fibres. Herein, a simple composite type torsional actuator made of hydrogel coated commercial textile cotton multifilament fibre is demonstrated. This novel actuator is of high moisture responsiveness, given that hydrogels are capable of providing huge volume expansion and twisting the overall system can transform the volumetric expansion to fibre untwisting based torsional actuation. Theoretical treatment of torsional actuation is also demonstrated based on the change in torsional stiffness of dry and wet fibres as well as a few externally applied torques. The agreement between experimental measurements and theoretical estimation is found reasonable, and the investigation allows the near-appropriate estimation of torsional stroke before integrating an actuator into a smart system.