Research ArticleMATERIALS SCIENCE

Iridescence-controlled and flexibly tunable retroreflective structural color film for smart displays

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Science Advances  09 Aug 2019:
Vol. 5, no. 8, eaaw8755
DOI: 10.1126/sciadv.aaw8755
  • Fig. 1 Fabrication and optical properties of the proposed RSCF.

    (A to D) Schematic illustration of the fabrication of an RSCF by transferring a monolayer array of PS microspheres from a substrate onto the sticky side of a transparent tape. (E) Typical cross-sectional SEM image of an RSCF assembled from 15-μm PS microspheres, showing that the microspheres are partially embedded in the polyacrylate adhesive layer of the tape. (F) Photographs of the tape side (path I) and microsphere side (path II) of the RSCF under diffuse daylight. (G) Photographs of the tape side (path I) and microsphere side (path II) of the RSCF under a white LED light source, showing a bright bluish green reflection color from the tape side. (H) Reflection optical micrograph of the RSCF observed from the tape side, showing a bluish green reflection circle from each microsphere. (I) Reflectance spectra measured from the tape and microsphere sides of the RSCF at normal incidence and reflection. Scale bars, 20 μm (E and H) and 1 cm (F and G).

  • Fig. 2 Color tunability of RSCFs.

    (A) Schematic illustration of the generation of retroreflective structural color in a single air-cushioned microsphere/polymer bilayer model. (B) Photographs of RSCFs assembled with 5- to 38-μm PS microspheres under normal illumination and viewing conditions. (C to E) Schematic illustrations (C), photographs (D), and angle-resolved reflectance spectra (E) of the non-iridescent colors reflected by an RSCF assembled from 15-μm PS microspheres under coaxial illumination and viewing conditions at different viewing angles α. (F to H) Schematic illustrations (F), photographs (G), and angle-resolved reflectance spectra (H) of the iridescent colors reflected by an RSCF assembled from 15-μm PS microspheres under oblique illumination at an angle of β and at a fixed viewing angle of 0°. (I) CIE chromaticity coordinates of the RSCF samples represented in (B), (D), and (G). Scale bars, 1 cm (B, D, and G).

  • Fig. 3 Comparison of the reflective properties.

    (A to C) Measured reflectance intensity of an RSCF (A), a commercial pigment-based glass bead-type retroreflective sheeting (B), and the wing of a P. blumei butterfly (C) under coaxial illumination and viewing conditions at different angles of α. (D to F) Measured reflectance intensity of the RSCF (D), the commercial retroreflective sheeting (E), and the P. blumei butterfly (F) under oblique illumination angle β and at a fixed viewing angle of 0°. (G) Photographs taken normal to the RSCF (left), the P. blumei butterfly (middle), and the commercial retroreflective sheeting (right) under diffuse daylight. (H to K) Photographs of the three samples taken under coaxial conditions at different viewing angles of 0° (H), 10° (I), 20° (J), and 30° (K). (L to O) Photographs taken normal to the three sample surfaces and at an oblique illumination angle of 1° (L), 5° (M), 10° (N), and 20° (O). Scale bars, 2 cm (G to O).

  • Fig. 4 Nighttime traffic safety and advertisement applications of RSCFs.

    (A and B) Photographs of a 1-m-long and 6-cm-wide RSCF fabricated from 15-μm PS microspheres, showing no color under diffuse daylight (A) but a bright green color under illumination by vehicle headlights at night (B). (C) A schematic model of a nighttime traffic scene in which a 60-cm triangular traffic sign fabricated from RSCFs is located on the roadside and illuminated by the headlights of a moving vehicle and a pedestrian is walking toward the traffic sign. (D to F) Photographs of the pedestrian’s view of the traffic sign when the distance L between the vehicle and the sign is 80 m (D), 50 m (E), and 30 m (F), demonstrating a smart color-changing visual indication that warns the pedestrian of the approaching vehicle. (G to I) Corresponding photographs of the driver’s view of the traffic sign at distances L of 80 m (G), 50 m (H), and 30 m (I), demonstrating that a saturated and stable color signal is presented to the driver. (J0 to J15) Wide variety of colors formed by depositing different sizes of PS and PMMA microspheres on polyacrylate-coated plexiglass plates. The photographs were taken normal to the sample surfaces and at an illumination angle from 0° (J0) to 15° (J15) at about every 1° interval. The words and symbols of the triangle sign and the circular sign in (D) to (I) were made with different RSCFs assembled from 13- and 15-μm PS microspheres and 15-μm PMMA microspheres. The nine-triangle plates in J0 to J15 were made with 7- to 18-μm PS microspheres and 15-μm PMMA microspheres. Scale bars, 10 cm (A and B), 30 cm (D to I), and 4 cm (J0 to J15). (Photo credit: Wen Fan, Fudan University)

  • Fig. 5 Flickering RSCF display at night.

    (A) Schematic model of an interactive speed limit sign fabricated from RSCFs. (B to F) Photographs showing the flickering effect of a normally illuminated speed limit sign viewed from the side window of a moving vehicle that is passing by the sign from right to left. The words and symbols of the sign were made with different RSCFs assembled from 6-, 7-, 8-, 9-, 10-, 13-, 15-, 15.5-, and 18-μm PS microspheres and 15-μm PMMA microspheres. Scale bars, 10 cm (B to F). Photo credit: Wen Fan, Fudan University.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/8/eaaw8755/DC1

    Section S1. Analysis of TIR condition

    Section S2. Microscopic characterization and analysis

    Section S3. Analysis of air-cushioned microsphere/polymer bilayer model

    Fig. S1. TIR condition.

    Fig. S2. Influence of the embedded depth/diameter ratios of PS microsphere on the reflectance spectra of RSCFs assembled from 15-μm PS microspheres.

    Fig. S3. Control experiments with 15-μm PS microspheres partially or completely embedded in the polyacrylate layer.

    Fig. S4. Analysis of PS microsphere/polyacrylate interface.

    Fig. S5. Comparison of the reflectance spectra between the freshly prepared (ambient temperature: 25°) and the overnight stored RSCF (ambient temperature: 20°) assembled from 15-μm PS microspheres.

    Fig. S6. Control experiments with 15-μm PS microspheres shallowly embedded in a thinner polyacrylate layer.

    Fig. S7. Spectral stability of the RSCF assembled from 15-μm PS microspheres.

    Fig. S8. Measured and simulated reflectance spectra of RSCFs.

    Fig. S9. RSCF-based cylindrical reflective delineators on a curved road.

    Fig. S10. RSCF-based billboard for drivers and pedestrians.

    Movie S1. The non-iridescent colors of RSCFs.

    Movie S2. The iridescent colors of RSCFs.

    Movie S3. Demonstration of the large illumination-to-viewing angle of RSCF in the noncoaxial case.

    Movie S4. RSCF-based cylindrical reflective delineators seen by a driver or a pedestrian.

    Movie S5. RSC-based billboard seen by a driver or a pedestrian.

    Movie S6. RSC-based interactive warning indicator.

  • Supplementary Materials

    The PDF file includes:

    • Section S1. Analysis of TIR condition
    • Section S2. Microscopic characterization and analysis
    • Section S3. Analysis of air-cushioned microsphere/polymer bilayer model
    • Fig. S1. TIR condition.
    • Fig. S2. Influence of the embedded depth/diameter ratios of PS microsphere on the reflectance spectra of RSCFs assembled from 15-μm PS microspheres.
    • Fig. S3. Control experiments with 15-μm PS microspheres partially or completely embedded in the polyacrylate layer.
    • Fig. S4. Analysis of PS microsphere/polyacrylate interface.
    • Fig. S5. Comparison of the reflectance spectra between the freshly prepared (ambient temperature: 25°) and the overnight stored RSCF (ambient temperature: 20°) assembled from 15-μm PS microspheres.
    • Fig. S6. Control experiments with 15-μm PS microspheres shallowly embedded in a thinner polyacrylate layer.
    • Fig. S7. Spectral stability of the RSCF assembled from 15-μm PS microspheres.
    • Fig. S8. Measured and simulated reflectance spectra of RSCFs.
    • Fig. S9. RSCF-based cylindrical reflective delineators on a curved road.
    • Fig. S10. RSCF-based billboard for drivers and pedestrians.
    • Legends for movies S1 to S6

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). The non-iridescent colors of RSCFs.
    • Movie S2 (.mp4 format). The iridescent colors of RSCFs.
    • Movie S3 (.mp4 format). Demonstration of the large illumination-to-viewing angle of RSCF in the noncoaxial case.
    • Movie S4 (.mp4 format). RSCF-based cylindrical reflective delineators seen by a driver or a pedestrian.
    • Movie S5 (.mp4 format). RSC-based billboard seen by a driver or a pedestrian.
    • Movie S6 (.mp4 format). RSC-based interactive warning indicator.

    Files in this Data Supplement:

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