Research ArticleAPPLIED SCIENCES AND ENGINEERING

Sequential self-folding of polymer sheets

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Science Advances  03 Mar 2017:
Vol. 3, no. 3, e1602417
DOI: 10.1126/sciadv.1602417
  • Fig. 1 Concept of differential light absorption for sequential folding.

    (A) Radar plot in which each wedge represents an ink color from a laserjet printer. Data points represent the optical absorption of the three wavelengths of LEDs used in this study: red (660 nm), green (530 nm), and blue (470 nm) LEDs. The data points are connected by lines to guide the eye. (B) Photographs for folding controlled in sequence by using hinges in yellow (in response to a blue LED) and cyan (in response to a red LED). Fifteen-watt LEDs were used at ~1.5 cm above the sample. (C) Bending angle as a function of LED exposure time for yellow and cyan hinges under the exposure of red and blue LEDs. (D) Photographs for folding controlled in sequence by using the hinges in magenta (in response to a green LED) and cyan (in response to a red LED). Fifteen-watt red LED was used at ~1.5 cm away from the sample, and 15-W green LED was used at a distance of 0.7 cm. The sample dimensions are 18 mm × 5 mm with a hinge width of 2 mm.

  • Fig. 2 Images of complex structures formed via sequential folding.

    (A) Nested boxes with a small box with green hinges (5 mm × 5 mm × 5 mm) on top of a large one with orange hinges (10 mm × 10 mm × 10 mm). (B) Unfolding pathway: Folding first occurs toward the top green hinge using a red LED. An orange hinge is patterned on the opposite side of the green hinge. Unfolding occurs by activating the orange hinge using a blue LED. (C) Supercoil formed in a polymer strip patterned with yellow (width, 1.5 mm) and cyan (width, 2.0 mm) diagonal stripes. Scale bars, 10 mm.

  • Fig. 3 Complex geometries via sequential folding.

    (A) Perspective schematic of star-shaped templates featuring a small star (black hinges) placed on the top of a medium-sized star (red hinges) placed on top of the largest star (walnut-colored hinges). All hinge widths are 2 mm. (B) Corresponding sequential folding of the three-layer lotus made of three stars with five hinges placed on top of each other. Onset time for these snapshots are 0 s (top) and 3, 4, 6, and 16 s (bottom) (see video S1 in the Supplementary Materials). (C) Photograph of a folded structure. (D) Schematic of a template featuring double hinges with black, red, and walnut colors patterned on a polymer sheet. Numbers 1 to 3 denote the designed folding order of the three panels. The double-line hinges are 2.0 mm wide with a spacing of 1.0 mm between the two lines. (E) Three independent but overlapping single folding panels self-fold sequentially. The double-hinge design facilitates folding up to 180°. Time for these snapshots are 1 s (top) and 2, 3, 5, 7, and 25 s (bottom) (see video S2 in the Supplementary Materials). (F) Photograph of a folded structure. Scale bars, 10 mm.

  • Fig. 4 Sequentially actuated kirigami 3D shapes.

    (A) Out-of-plane and in-plane structures are actuated sequentially by shrinking the outer ring (yellow) first to achieve out-of-plane motion and then shrinking the inner ring (cyan) to flatten the sample again. Living hinges connect the two circular rings. (B) The spiral structure forms by first pushing upward the bottom because of the shrinkage of the yellow ring and subsequently pushing upward the middle layer because of the shrinkage of the cyan ring. Images in the boxes with dashed lines show the temporary shape formed by irradiating with blue LED and then the shape formed by irradiating with a red LED sequentially. The final shape represents a side view of the spiral. (C) A dome structure results by applying inks with different optical absorption under a blue LED. The samples are held at 90°C in a custom-built convection oven during folding. Scale bars, 5 mm.

  • Fig. 5 Generalized onset time and bending angle.

    Effect of light intensity absorbed by the hinge on (A) the onset of folding and (B) of bending angle for blue (squares) and red (circles) LEDs. The symbol colors correspond to the color of the inks printed as hinges, as described in table S2 (color code). Onset times and bending angles refer to hinges printed on Grafix polymer sheets using the setup detailed in Materials and Methods. Inset depicts the zoom-in plot for the data with onset time of 0 to 8 s. The sample dimensions are 25 mm × 10 mm with a central hinge width of 2 mm.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/3/e1602417/DC1

    fig. S1. Optical absorption spectra of color inks printed on a plain prestrained polymer sheet.

    fig. S2. Thickness of hinges printed with different colors using an HP Color LaserJet CP3525dn printer on Grafix polymer sheets.

    table S1. Measured power density for different LEDs used for the folding test.

    table S2. CMYK codes for different colors.

    video S1. Sequential self-folding of three star-shaped templates placed on top of each other using a blue LED.

    video S2. Sequential self-folding of a template featuring double hinges with different colors on the three panels to fold up to 180°.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Optical absorption spectra of color inks printed on a plain prestrained polymer sheet.
    • fig. S2. Thickness of hinges printed with different colors using an HP Color LaserJet CP3525dn printer on Grafix polymer sheets.
    • table S1. Measured power density for different LEDs used for the folding test.
    • table S2. CMYK codes for different colors.
    • Legends for videos S1 and S2

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    Other Supplementary Material for this manuscript includes the following:

    • video S1 (.mp4 format). Sequential self-folding of three star-shaped templates placed on top of each other using a blue LED.
    • video S2 (.mp4 format). Sequential self-folding of a template featuring double hinges with different colors on the three panels to fold up to 180°.

    Files in this Data Supplement:

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