Research ArticleMATERIALS SCIENCE

A readily programmable, fully reversible shape-switching material

See allHide authors and affiliations

Science Advances  24 Aug 2018:
Vol. 4, no. 8, eaat4634
DOI: 10.1126/sciadv.aat4634
  • Fig. 1 Photopolymerizable AFT-LCEs were programmable and erasable.

    (A) Thiol-Michael addition reaction scheme to install RAFT functional groups into photopolymerizable acrylic oligomers. (B) LCEs were aligned and subsequently erased by applying a mechanical bias (programming) or a thermal disruption (erasing) coupled with light (hv, 30 mW/cm2, 320 to 500 nm). The polar graph presents the polarized Fourier transform infrared spectroscopy (FTIR) peak area corresponding to C–H on the aromatic core (3350 to 3300 cm−1) at various light polarization angles. Each line represents the following: as-polymerized polydomain (•), programmed (30-s hv, 100% strain, cycle 1, □), erased cycle 1 (30-s hv, 120°C, cycle 1, ▪), programmed (30-s hv, 100% strain, cycle 2,▵), and erased (60-s hv, 120°C, cycle 2, ▴). Programming was done parallel to 90°. (C) Example of programming process starting from a polydomain 250-μm-thick polymer. The polymer was folded by hand and programmed with 320 to 500 nm (100 mW/cm2) coupled with gentle heating (30° to 40°C). Subsequent thermal cycling resulted in the network unfolding at high temperatures and folding during cooling (movie S1).

  • Fig. 2 Final LC and isotropic phase shape after programming under various conditions.

    (A) Strain relative to initial shape in the LC state after programming for various exposure times (320 to 500 nm, 30 mW/cm2) at 25°C (•), 67°C (▴), and 120°C (▪). Programming strain was set at 45 ± 10% except for 120°C samples, which were set at 15 ± 5%. (B) Strain in the isotropic state measured at 120°C after programming for various exposure times (320 to 500 nm, 30 mW/cm2) at 25°C (•), 67°C (▴), and 120°C (▪). (C) Strain in LC state (•) and isotropic state (▪) after programming (320 to 500 nm, 30 mW/cm2, 300 s) at room temperature at various exposure strains. (D) Schematic representation of the experiment. Beginning from ε0, the sample is stretch (1) to the applied strain (εapplied) and heated to the appropriate temperature (blue denotes 25°C and red denotes both 67° and 120°C). After light exposure and release of strain (2), the sample was thermally cycled to measure the programmed strain in the LC phase (εLC,P) and isotropic phase (εI,P).

  • Fig. 3 Controllable shape changes in AFT-LCEs.

    (A) With inclusion of a photoabsorber, programming of optically thick samples results in thermoreversible bending. The graph depicts bending angle after various irradiation times at room temperature (365 nm, 50 mW/cm2; 20% strain). (B) Starting from a thermally quenched, programmed LCE, the temporary shape was programmed by stretching perpendicular to the light programmed direction (A). The molded sample was then heated (B), revealing the intermediate square shape, and upon cooling, spontaneously returned to the light-programmed LC shape (programming, 365 nm, 30 mW/cm2). (C) A box was programmed as the temporary shape and unfolded after heating. After cooling, the LCE autonomously folded into a swan, as previously programmed with light (365 nm, 50 mW/cm2; 300 s).

  • Fig. 4 Thermoreversible shape change programmed by nanoimprinting.

    (A) Atomic force microscopy (AFM) images taken at 35° and 99°C for a diffraction grating programmed at 55°C with 3 MPa and 300- to 400-nm (20 mW/cm2) light for 1 min. The images are 10 μm × 10 μm with the z axis color scale shown at the right (17 to −17 nm). (B) AFM images taken at 35° and 99°C of a diffraction grating programmed at 99°C, followed by a second, flat programming step at 55°C with same irradiation conditions as in (A). (C) Diffraction efficiency as a function of temperature for grating programmed at 55°C. This sample corresponds to the AFM images shown in (A).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/8/eaat4634/DC1

    Fig. S1. Mechanism of allyl sulfide exchange.

    Fig. S2. Thermomechanical analysis of LCEs.

    Fig. S3. Reprogramming of the LC shape.

    Fig. S4. A square peg morphs into a round peg when heated into the isotropic phase.

    Fig. S5. Strain to break experiments for 1:0.5:1.35 RM82/NPGDA/allyl dithiol.

    Fig. S6. Polarized optical microscopy of unprogrammed and programmed LCEs.

    Fig. S7. Stress relaxation behavior of LCE at 120°C (gray), 67°C (blue), and 25°C (red).

    Fig. S8. Heat coupled with light-erased programmed LC strain.

    Fig. S9. Stress relaxation in the isotropic shape with and without load.

    Fig. S10. Folded structure developed by programming each face separately.

    Fig. S11. Patterned alignment results in surface topography.

    Movie S1. A programmed LCE folds and unfolds during thermal cycling.

    Movie S2. A square peg falling through a circular hole.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Mechanism of allyl sulfide exchange.
    • Fig. S2. Thermomechanical analysis of LCEs.
    • Fig. S3. Reprogramming of the LC shape.
    • Fig. S4. A square peg morphs into a round peg when heated into the isotropic phase.
    • Fig. S5. Strain to break experiments for 1:0.5:1.35 RM82/NPGDA/allyl dithiol.
    • Fig. S6. Polarized optical microscopy of unprogrammed and programmed LCEs.
    • Fig. S7. Stress relaxation behavior of LCE at 120°C (gray), 67°C (blue), and 25°C (red).
    • Fig. S8. Heat coupled with light-erased programmed LC strain.
    • Fig. S9. Stress relaxation in the isotropic shape with and without load.
    • Fig. S10. Folded structure developed by programming each face separately.
    • Fig. S11. Patterned alignment results in surface topography.
    • Legends for movies S1 and S2

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). A programmed LCE folds and unfolds during thermal cycling.
    • Movie S2 (.mp4 format). A square peg falling through a circular hole.

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article