Research ArticlePHYSICS

Scanning wave photopolymerization enables dye-free alignment patterning of liquid crystals

See allHide authors and affiliations

Science Advances  10 Nov 2017:
Vol. 3, no. 11, e1701610
DOI: 10.1126/sciadv.1701610
  • Fig. 1 Schematic representations of photoirradiation for controlling molecular alignment.

    (A) Conventional photoalignment method via the interaction between linearly polarized light and photoresponsive dye molecules (red rod) and simultaneous cooperative effect to align LCs (yellow rod), where light is spatiotemporally uniform. (B) New concept proposed here for generating molecular alignment merely by photopolymerization with spatiotemporal scanning of light patterns, termed “SWaP.” Pink and black regions represent irradiated and unirradiated regions, respectively.

  • Fig. 2 Characterization of molecular alignment driven by SWaP of sample 1.

    (A) Chemical structures of materials used. The structures colored by orange rectangles are compounds for sample 1. (B) POM images rotated by 45° from one another under crossed polarizers. Scale bars, 100 μm. Yellow arrows indicate the light scanning direction; black and white arrows depict the direction of the polarizers. (C) Polarized UV-vis absorption spectra, (D) a polar plot of UV-vis absorbance, and (E) polarized IR absorption spectra of a resultant film photopolymerized with light through a 250-μm slit scanned in 1D at 20 μm/s. For (C) and (D), the polar plot and order parameter are evaluated by averaging the UV-vis absorbance in a range of wavelength from 332 to 350 nm, measured by rotating the film every 5°. For (C) and (E), the azimuthal angle θ is defined as 0° for A|| and 90° for A when the polarizing direction of incident light is parallel and perpendicular to the light scanning direction. a.u., arbitrary units.

  • Fig. 3 Evidence that molecular diffusion drives alignment.

    (A) Schematic illustrations of the generation of molecular alignment during SWaP where a mass flow triggered by photopolymerization aligns both the mesogenic side-chain units (yellow rod) and the polymer main chains (white curves) over large areas depending on scanning light. (B) A schematic illustration of photopolymerization at the boundary (blue line) of two mixtures injected into a glass cell from separate sides. (C) POM images under crossed polarizers offset 0° (top) and −45° (bottom) from vertical of resultant films photopolymerized 180 s after contacting the two mixtures. Red arrows show the injection direction; white arrows show the direction of polarizers. Scale bar, 200 μm. (D) Alignment length and birefringence emerged as a function of flow duration compared with a theoretical model.

  • Fig. 4 Arbitrary alignment patterns developed by spatiotemporal scanning of light.

    (A) Schematic illustrations of desired patterns of alignment of mesogenic side-chain unit (yellow rod). (B) Irradiated light patterns: (I) toroid shape expanding at 27.4 μm/s with a width of 247 μm and a diameter of 493 μm in the initial state; (II) periodic dots scanned in 1D at 27.4 μm/s with a diameter of 137 μm and a center-to-center distance of 206 μm; and (III) the words “Tokyo Tech” where 178-μm-wide light was scanned at 13.7 mm/s and an exposure time of 1 min. White and black areas represent irradiated and unirradiated regions. The yellow arrows show the scanning direction, and the numbers denote the scanning order. (C) POM images under crossed polarizers. White arrows show the direction of polarizers.

  • Fig. 5 High-resolution patterning of molecular alignment by SWaP.

    (A) An optical pattern of a square lattice with a lattice point distance of 27.4 μm and an irradiated region width of 13.7 μm (left), and POM images of the resultant polymer film displaying an array of microscopic radial molecular alignment (right). (B) Photograph of a test target used as a photomask having the highest resolution of ~2-μm line space (left), and a POM image of the resultant polymer film (right). For (B), the bottom images are higher magnifications of the top images. White arrows show the direction of polarizers.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/11/e1701610/DC1

    text S1. Synthesis of 4′-hydroxyhexyl-4-cyanobiphenyl (compound 1)

    text S2. Synthesis of 4′-[6-(methacryloyloxy)hexyloxy]-4-cyanobiphenyl (M4)

    text S3. Theoretical estimation of molecular alignment length

    fig. S1. Schematic illustrations of the optical setup for SWaP.

    fig. S2. UV-vis absorption spectra of monomers, guest molecules, and photoinitiators in THF.

    fig. S3. Representative 1H NMR spectrum of a sample of 1.

    fig. S4. A plot of transmittance as a function of wavelength to determine the thickness of a handmade glass cell.

    fig. S5. The effect of cell thickness on molecular alignment behavior in SWaP of sample 1.

    fig. S6. DSC thermograms of monomers and homopolymers.

    fig. S7. Effect of photopolymerization temperature on molecular alignment behavior in SWaP of sample 1.

    fig. S8. Thermal memory effect on molecular alignment generated by SWaP of sample 1.

    fig. S9. Photopolymerization of sample 1 without spatiotemporal scanning of light.

    fig. S10. Schematic illustration of the optical setup for in situ observation during SWaP.

    fig. S11. Effect of the light scanning rate on the order parameter (S) in SWaP of sample 1.

    fig. S12. Demonstration of the generality of SWaP for various chemical systems with the 4f optical setup with a high-pressure mercury lamp.

    fig. S13. Demonstration of the robustness of SWaP using cationic polymerization.

    fig. S14. GPC chromatogram for PM4 (Mn = 8000) detected at 300 nm.

    fig. S15. Emergence of molecular alignment without SWaP in the test case.

    fig. S16. Theoretical model of alignment length and molecular diffusion length in the test case estimated from Fick’s law of diffusion.

    fig. S17. Two dimensional and 3D intensity profiles of the representative patterns irradiated with a DMD captured with a charge-coupled device beam profiler.

    table S1. Composition ratios of materials and thermodynamic properties of the samples used in this study.

    table S2. Molecular weights of polymers prepared by ATRP.

    movie S1. In situ observation of SWaP with 1D scanned slit light of sample 1.

    movie S2. In situ observation of static photopolymerization with slit light of sample 1.

    movie S3. An irradiated pattern designed by Illustrator software for SWaP with a 2D expanding “toroid-shape.”

    movie S4. An irradiated pattern designed by Illustrator software for SWaP with a 1D scanning of periodic dots.

    movie S5. An irradiated pattern designed by Illustrator software for SWaP with 2D scanning along various letters.

  • Supplementary Materials

    This PDF file includes:

    • text S1. Synthesis of 4′-hydroxyhexyl-4-cyanobiphenyl (compound 1)
    • text S2. Synthesis of 4′-6-(methacryloyloxy)hexyloxy-4-cyanobiphenyl (M4)
    • text S3. Theoretical estimation of molecular alignment length
    • fig. S1. Schematic illustrations of the optical setup for SWaP.
    • fig. S2. UV-vis absorption spectra of monomers, guest molecules, and photoinitiators in THF.
    • fig. S3. Representative 1H NMR spectrum of a sample of 1.
    • fig. S4. A plot of transmittance as a function of wavelength to determine the thickness of a handmade glass cell.
    • fig. S5. The effect of cell thickness on molecular alignment behavior in SWaP of sample 1.
    • fig. S6. DSC thermograms of monomers and homopolymers.
    • fig. S7. Effect of photopolymerization temperature on molecular alignment behavior in SWaP of sample 1.
    • fig. S8. Thermal memory effect on molecular alignment generated by SWaP of sample 1.
    • fig. S9. Photopolymerization of sample 1 without spatiotemporal scanning of light.
    • fig. S10. Schematic illustration of the optical setup for in situ observation during SWaP.
    • fig. S11. Effect of the light scanning rate on the order parameter (S) in SWaP of sample 1.
    • fig. S12. Demonstration of the generality of SWaP for various chemical systems with the 4f optical setup with a high-pressure mercury lamp.
    • fig. S13. Demonstration of the robustness of SWaP using cationic polymerization.
    • fig. S14. GPC chromatogram for PM4 (Mn = 8000) detected at 300 nm.
    • fig. S15. Emergence of molecular alignment without SWaP in the test case.
    • fig. S16. Theoretical model of alignment length and molecular diffusion length in the test case estimated from Fick’s law of diffusion.
    • fig. S17. Two dimensional and 3D intensity profiles of the representative patterns irradiated with a DMD captured with a charge-coupled device beam profiler.
    • table S1. Composition ratios of materials and thermodynamic properties of the samples used in this study.
    • table S2. Molecular weights of polymers prepared by ATRP.
    • Legends for movies S1 to S5

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.avi format). In situ observation of SWaP with 1D scanned slit light of sample 1.
    • movie S2 (.avi format). In situ observation of static photopolymerization with slit light of sample 1.
    • movie S3 (.avi format). An irradiated pattern designed by Illustrator software for SWaP with a 2D expanding “toroid-shape.”
    • movie S4 (.avi format). An irradiated pattern designed by Illustrator software for SWaP with a 1D scanning of periodic dots.
    • movie S5 (.avi format). An irradiated pattern designed by Illustrator software for SWaP with 2D scanning along various letters.

    Files in this Data Supplement: