Research ArticleMATERIALS SCIENCE

Monolithic shape-programmable dielectric liquid crystal elastomer actuators

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Science Advances  22 Nov 2019:
Vol. 5, no. 11, eaay0855
DOI: 10.1126/sciadv.aay0855
  • Fig. 1 Device schematic, mechanical, and electrical characterization.

    (A) Schematic of a traditional isotropic DE actuator in off and on states. (B) Schematic of a uniaxial aligned dielectric LCE actuator (DLCEA) in off and on states. Liquid crystal molecular alignment; the director, n, is indicated by a double-headed arrow and defines the stiffer direction of the LCE. When actuated by a voltage, V, the material thins and stretches perpendicular to the alignment greater than parallel to the director. (C) The DLCEA mechanical stress and normalized capacitance (C) response to strain over the DLCEA linear regime are characterized at a strain rate of 0.1% per second.

  • Fig. 2 Characterization of uniaxial DLCEA demonstrates the capabilities of a DLCEA actuator device.

    (A) Isometric (constant strain) tests. Measured active nominal stress reduction with various initial isometric strains (u) for devices assembled with the LCE director nu and nu and a photograph of an assembled DLCEA device with nu. (B) Isotonic (constant force) tests. Contractile discharge strain trajectories under various loads measured by a high-speed camera with actuation voltages of 3 kV. Inset: The corresponding measurements of electrical discharge. (C) Fundamental actuator characteristics are computed from the contraction trajectory and measurement of the discharge current found in (B), including strain (u), peak strain rate (u˙peak), peak specific power (P^peak), specific energy (E^), and efficiency. Photo credits: Zoey S. Davidson.

  • Fig. 3 Uniaxial out-of-plane buckling DLCEA.

    (A) Off and (B) on states of a uniaxial DLCEA device with fixed boundary condition. Expansion along the soft direction creates out-of-plane buckling, which displaces a fine thread held taut across the surface. (C) Experimental measurement of buckling as a function of the applied voltage. (D) Frequency response of buckling uniaxial DLCEA at 1 kV. The 0.1-Hz actuation amplitude is approximately 130 μm.

    Photo credits: Zoey S. Davidson.
  • Fig. 4 Pixelated DLCEA.

    Programmed shape actuation, such as a dimple pattern deformation, is possible by patterning the director configuration into an azimuthal-radial defect lattice. (A) Azimuthal defect types deform into a cone with locally positive Gaussian curvature, and (B) radial defect types deform into an anti-cone with locally negative (saddle-like) Gaussian curvature. In (A) and (B), the double-headed red arrows indicate the soft direction. (C) The defects are patterned using a pixelated array of polarizing films with the designed local orientations. (D) Viewed through crossed polarizers, the fabricated LCE film has pixelated uniaxial alignment, indicated by dashed white lines, forming a defect lattice. (E) When charged to 2.5 kV, there is a large visible deformation of the surface. (F) The profilometry measured height map of the grease-covered LCE is nearly flat with no charge and varies over 1.6 mm when charged to 2.5 kV. The dash-dot and dash circles in (F) are traces of height depicted in (G). The change from approximately constant height to a sinusoidally varying height indicates a change in sign of the local Gaussian curvature. Scale bars, 4 mm. Photo credits: Zoey S. Davidson.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/11/eaay0855/DC1

    Fig. S1. Optical characterization of uniaxially aligned LCE.

    Fig. S2. Photograph of laser-cut regions of LCE and measured heights.

    Fig. S3. Stress-strain characterization of uniaxial LCE.

    Fig. S4. Assembly process for typical uniaxial DLCEA build.

    Fig. S5. Schematic of DLCEA with coordinate axes and simulation results.

    Fig. S6. Isometric uniaxial DLCEA relaxation and log-log stress-voltage relation.

    Fig. S7. Isopotential tests of uniaxial DLCEA.

    Fig. S8. Schematic of high-voltage switching mechanism, isotonic full cycle actuation, and isotonic actuation characteristics with varying voltage.

    Fig. S9. Uniaxially buckling DLCEA voltage and frequency response.

    Fig. S10. Actuation of LCE films with a twisted configuration.

    Movie S1. Uniaxial DLCEA with director parallel to Fg.

    Movie S2. Uniaxial DLCEA with director perpendicular to Fg.

    Movie S3. Demonstration of uniaxial buckling DLCEA.

    Movie S4. Demonstration of programmable shape change buckling DLCEA.

  • Supplementary Materials

    The PDFset includes:

    • Fig. S1. Optical characterization of uniaxially aligned LCE.
    • Fig. S2. Photograph of laser-cut regions of LCE and measured heights.
    • Fig. S3. Stress-strain characterization of uniaxial LCE.
    • Fig. S4. Assembly process for typical uniaxial DLCEA build.
    • Fig. S5. Schematic of DLCEA with coordinate axes and simulation results.
    • Fig. S6. Isometric uniaxial DLCEA relaxation and log-log stress-voltage relation.
    • Fig. S7. Isopotential tests of uniaxial DLCEA.
    • Fig. S8. Schematic of high-voltage switching mechanism, isotonic full cycle actuation, and isotonic actuation characteristics with varying voltage.
    • Fig. S9. Uniaxially buckling DLCEA voltage and frequency response.
    • Fig. S10. Actuation of LCE films with a twisted configuration.
    • Legends for movies S1 to S4

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Uniaxial DLCEA with director parallel to Fg.
    • Movie S2 (.mp4 format). Uniaxial DLCEA with director perpendicular to Fg.
    • Movie S3 (.mp4 format). Demonstration of uniaxial buckling DLCEA.
    • Movie S4 (.mp4 format). Demonstration of programmable shape change buckling DLCEA.

    Files in this Data Supplement:

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