Hydro-actuation of hybrid carbon nanotube yarn muscles.

Hybrid hydro-responsive actuators are developed by infiltrating carbon nanotube yarns using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate). These actuators demonstrate impressive rotation and contraction in response to water due to volumetric expansion of the helical arrangement of carbon nanotubes. The total torsional stroke is 3720 revolutions per m and the simultaneously generated contractive strain reaches 24% at a paddle-to-yarn mass ratio of 350. The contraction output can furthermore be significantly enhanced by constraining the rotational motion and it reaches 68% with an applied stress of 1 MPa. Additionally, hybrid yarns exhibit an approximately linear response to humidity changes and show extra capability of electrical actuation, which, combined with the excellent hydro-actuation performance, endow them with great potential for a variety of applications including artificial muscles, hydro-driven generators, moisture switches and microfluidic mixers.