▎ 摘　　要

Encoding a helical shape into straight fibers could bring unprecedented properties and explore applications in a broad range of areas; this has been difficult for graphene oxide (GO) fibers due to their relatively poor mechanical property and processability. Here, we incorporate a continuous single-walled carbon nanotube (SWNT) network into dispersed GO sheets to fabricate GO/SWNT composite films and helical fibers with an alternating layered structure. Our GO/SWNT fibers combine advantages from both the SWNTs (as a robust and conductive skeleton) and GO (as a hydrophilic matrix), leading to reversible mechanical actuation with axial contraction up to 50% of original fiber length in response to water adsorption. The structural evolution (including increase in fiber diameter and decrease in the helical loop number) is a key factor for generating large axial contraction. Graphene-based helical fibers embedding a continuous carbon nanotube network, as described here, have potential applications in flexible/wearable electronics, sensors and actuators. (c) 2018 Elsevier Ltd. All rights reserved.