Research ArticleBIOMIMETICS

Light-stimulated actuators based on nickel hydroxide-oxyhydroxide

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Science Robotics  30 May 2018:
Vol. 3, Issue 18, eaat4051
DOI: 10.1126/scirobotics.aat4051
  • Fig. 1 Characteristics of the Ni(OH)2-NiOOH actuator.

    (A) Schematic diagram of the Ni(OH)2-NiOOH turbostratic crystal structure in which water molecules intercalated between the crystal planes. (B) Photo of the actuator and (C) its cross section in SEM exhibiting a layered structure. (D) TEM image of Ni(OH)2-NiOOH showing a crumpled microstructure.

  • Fig. 2 Response of the actuator to different stimulations.

    (A) Actuation induced by UV, Vis, and NIR lights at 10 mW/cm2. (B) QCM measurement of Ni(OH)2-NiOOH showing a mass increase under humid environment and a mass decrease upon the light illumination. (C) Photos of the oxidized (top) and reduced (bottom) actuator at different RHs. (D) Schematic diagram of Joule heating experiment and the heat-induced actuation of an actuator with size of about 30 × 25 mm2 under 1.5-A electrical current.

  • Fig. 3 Actuating properties of Vis light–induced actuation.

    (A) Vis light–induced actuation at increasing intensity from 5 to 100 mW/cm2. (B) Actuating speed, measured in degrees per second, for the bending and curling of the actuator measured from individual actuation tests plotted against the Vis light intensity used. (C) Schematic diagram for the calculation of the intrinsic actuating strain of the Ni(OH)2-NiOOH layer (not drawn to scale). Left: Unactuated state showing the coordinate system and the symbols for the dimensions. Middle: Intrinsic actuating strain εi under light illumination if the Ni(OH)2-NiOOH actuating layer was freed from the substrate. Right: Actuation in reality as the Ni(OH)2-NiOOH actuating layer bends forward to a radius of curvature R. (D) Calculated intrinsic actuating strain and stress of the Ni(OH)2-NiOOH layer corresponding to the actuation plotted against Vis light intensity. The data points represent the mean value of the intrinsic actuating strain and stress obtained from the measurement of 10 cycles of actuation. The error bars show the values resulted from the range of the measurement.

  • Fig. 4 Actuation performance induced by Vis light.

    (A) Change in force measured by a microtensile tester under periodic Vis light of 10 mW/cm2 and (B) the corresponding actuating force and stress plotted against the preload. The data points represent the mean value of the force and stress obtained from the measurement of 10 cycles of actuation. The error bars show the values resulted from the range of the measurement. (C) Schematic diagram of an actuator with three actuating hinges fabricated by plating at selected areas, and the self-folding and weight-lifting actuation under Vis light at 50 mW/cm2 (scale bars, 10 mm). (D) Vertical displacements of the weight-lifting actuation under different light intensities.

  • Fig. 5 Potential applications of the light-induced actuator.

    (A) Schematic diagram of the sunlight-induced actuation experiment and (B) demonstration of the sunlight-induced actuation at ~15 mW/cm2. (C) Biomimicked sensitive plant under NIR light of 200 mW/cm2 and (D) hairs by patterned plating under Vis light of 100 mW/cm2. (E) Schematic diagram of an actuator with two hinges that serves as a walking bot capable of walking toward flashing Vis light of ~50 mW/cm2. Scale bars, 5 mm.

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/3/18/eaat4051/DC1

    Fig. S1. Schematic diagrams of the fabrication of the actuators.

    Fig. S2. Cyclic voltammogram of the actuator under 1 M NaOH.

    Fig. S3. Electrochemical actuation under 1 M NaOH.

    Fig. S4. SEM images of the top view of an actuator.

    Fig. S5. EDS mapping of the cross section of an actuator.

    Fig. S6. SAED of oxidized and reduced Ni(OH)2-NiOOH.

    Fig. S7. GIXRD spectrum of oxidized and reduced Ni(OH)2-NiOOH.

    Fig. S8. Experimental setup for the light-induced actuation tests.

    Fig. S9. Light absorption spectra measured by UV-Vis spectroscopy.

    Fig. S10. Comparison of light-induced actuation of actuators with Ni and Ni-Au substrate under Vis light.

    Fig. S11. Actuation tests under Vis light at narrowband wavelengths.

    Fig. S12. Schematic diagram of the QCM cell.

    Fig. S13. Shape control of the actuator by redox reactions under the same RH.

    Fig. S14. Intrinsic actuating work density of the Ni(OH)2-NiOOH layer plotted against the Vis light intensity.

    Fig. S15. Long-term stability test of the intrinsic actuating strain.

    Fig. S16. Schematic diagram of the UTM tensile tester for the actuating force measurement under periodic Vis light illumination.

    Fig. S17. Vertical displacement of the weight-lifting actuation plotted against the change in time after light on/off.

    Movie S1. Electrochemical actuation of an actuator.

    Movie S2. Light-actuation of an actuator by UV, Vis, and NIR light.

    Movie S3. A demonstration of the humidity sensitivity of an actuator.

    Movie S4. A demonstration of the Joule heating–induced actuation of an actuator.

    Movie S5. Light-actuation of an actuator induced by Vis light at 5 to 50 mW/cm2.

    Movie S6. Light-actuation of an actuator induced by Vis light at 100 mW/cm2 with slow motion.

    Movie S7. Cyclic actuation test of an actuator for 5000 cycles.

    Movie S8. A demonstration of a hinged actuator capable of self-folding and weight lifting under Vis light.

    Movie S9. A demonstration of the sunlight-induced actuation of an actuator.

    Movie S10. A demonstration of a mimicked sensitive plant with rapid leaf movement.

    Movie S11. A demonstration of mimicked hairs that stand and fall under light stimulation.

    Movie S12. A demonstration of a walking bot under a horizontal flashing Vis light source.

    Movie S13. A demonstration of the shadowing effect on a walking bot under a horizontal flashing Vis light source.

  • Supplementary Materials

    Supplementary Material for:

    Light-stimulated actuators based on nickel hydroxide-oxyhydroxide

    K. W. Kwan, S. J. Li, N. Y. Hau, Wen-Di Li, S. P. Feng, Alfonso H. W. Ngan*

    *Corresponding author. Email: hwngan{at}hku.hk

    Published 30 May 2018, Sci. Robot. 3, eaat4051 (2018)
    DOI: 10.1126/scirobotics.aat4051

    This PDF file includes:

    • Fig. S1. Schematic diagrams of the fabrication of the actuators.
    • Fig. S2. Cyclic voltammogram of the actuator under 1 M NaOH.
    • Fig. S3. Electrochemical actuation under 1 M NaOH.
    • Fig. S4. SEM images of the top view of an actuator.
    • Fig. S5. EDS mapping of the cross section of an actuator.
    • Fig. S6. SAED of oxidized and reduced Ni(OH)2-NiOOH.
    • Fig. S7. GIXRD spectrum of oxidized and reduced Ni(OH)2-NiOOH.
    • Fig. S8. Experimental setup for the light-induced actuation tests.
    • Fig. S9. Light absorption spectra measured by UV-Vis spectroscopy.
    • Fig. S10. Comparison of light-induced actuation of actuators with Ni and Ni-Au substrate under Vis light.
    • Fig. S11. Actuation tests under Vis light at narrowband wavelengths.
    • Fig. S12. Schematic diagram of the QCM cell.
    • Fig. S13. Shape control of the actuator by redox reactions under the same RH.
    • Fig. S14. Intrinsic actuating work density of the Ni(OH)2-NiOOH layer plotted against the Vis light intensity.
    • Fig. S15. Long-term stability test of the intrinsic actuating strain.
    • Fig. S16. Schematic diagram of the UTM tensile tester for the actuating force measurement under periodic Vis light illumination.
    • Fig. S17. Vertical displacement of the weight-lifting actuation plotted against the change in time after light on/off.
    • Legends for movies S1 to S13

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mov file). Electrochemical actuation of an actuator.
    • Movie S2 (.mov file). Light-actuation of an actuator by UV, Vis, and NIR light.
    • Movie S3 (.mov file). A demonstration of the humidity sensitivity of an actuator.
    • Movie S4 (.mov file). A demonstration of the Joule heating–induced actuation of an actuator.
    • Movie S5 (.mov file). Light-actuation of an actuator induced by Vis light at 5 to 50 mW/cm2.
    • Movie S6 (.mov file). Light-actuation of an actuator induced by Vis light at 100 mW/cm2 with slow motion.
    • Movie S7 (.mov file). Cyclic actuation test of an actuator for 5000 cycles.
    • Movie S8 (.mov file). A demonstration of a hinged actuator capable of self-folding and weight lifting under Vis light.
    • Movie S9 (.mov file). A demonstration of the sunlight-induced actuation of an actuator.
    • Movie S10 (.mov file). A demonstration of a mimicked sensitive plant with rapid leaf movement.
    • Movie S11 (.mov file). A demonstration of mimicked hairs that stand and fall under light stimulation.
    • Movie S12 (.mov file). A demonstration of a walking bot under a horizontal flashing Vis light source.
    • Movie S13 (.mov file). A demonstration of the shadowing effect on a walking bot under a horizontal flashing Vis light source.

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