An ultrasensitive moisture driven actuator based on small flakes of graphene oxide

Moisture driven actuators with sensitive and strong actuation performances have important applications in robots, artificial muscles and hygrometers, etc. Here, we report such an actuator constructed by one layer of small flakes of graphene oxide (SGO) with an average lateral dimension of 0.9 μm and another layer of reduced conventional graphene oxide sheets (rCGO). An SGO film can adsorb about 22% (by weight, wt%) of water compared with its own weight by changing relative humidity (RH) from 20% to 50%. This SGO film can generate a contractile stress up to 90 MPa as relative humidity (RH) changed from 100% to 23%. An SGO/rCGO bilayer actuator with a thickness of 2.3 μm displayed an extremely large curvature (about 19.1 cm−1) at an RH of 98%. This actuator also exhibited a high rate of bending (4.4 cm−1 s−1) in the first second as RH switched from 75% to 32%. It showed excellent stability (kept unchanged after actuating for 1000 cycles), and was capable of moving an object 30 times heavier than its own weight.