Mechanism of Actuation in Nickel Hydroxide/Oxyhydroxide Photoactuators

Understanding novel actuating materials which respond to a variety of stimuli is key in the development of micro/nanoscale robotics. In this work, the mechanism of actuation in nickel hydroxide/oxyhydroxide actuators by the intercalation/deintercalation of water is examined. This effect is studied under the stimuli of visible light, photoactuation, and by increased environmental temperature, thermoactuation. The photoactuation is modelled using a mechanical model, and it is demonstrated that the experimentally observed intrinsic strain can be achieved with a low deintercalation of water, around 1%. This low level of water exchange is supported by structural changes observed during heating using thin film X‐ray diffraction (XRD), as well as time of flight secondary ion mass spectrometry (ToF‐SIMS) by isotopic exchange using D2O. These results show the water intercalation hypothesis is both possible and measurable. Future development must take this mechanism into account when designing materials for improved actuation performance. The mechanism of actuation in Ni(OH)2/NiOOH photoactuators is studied. The actuation is shown to be through the intercalation/deintercalation of water from the surroundings. High intrinsic strain is shown to be possible at very low levels of water exchange, around 1%. This has been confirmed via thin film X‐ray diffraction (XRD) and time of flight secondary ion mass spectrometry (ToF‐SIMS).