Research ArticleMATERIALS SCIENCE

3D touchless multiorder reflection structural color sensing display

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Science Advances  22 Jul 2020:
Vol. 6, no. 30, eabb5769
DOI: 10.1126/sciadv.abb5769
  • Fig. 1 Interpenetrated hydrogel network block copolymer photonic crystal.

    (A) Schematic illustration of BCP PC display with multiorder reflection SCs. Visible range SC of BCP PC is realized with the interpenetrated hydrogel network (IHN) of PEGDA in PQ2VP domains. By using nonvolatile ionic liquid of either EMITFSI or LiTFSI in IHN BCP PC, richer SCs are developed by mixing of multiorder reflection SCs. (B) Ultraviolet-visible (UV-vis) spectra of IHN BCP PC films on the glass as a function of UV exposure time. (C) Plot of the wavelength at maximum reflection as a function of UV exposure time from 10 to 60 s. (D) Photographs of IHN BCP PC film on glass substrates as a function of UV exposure time. The right end photograph shows its maximum reflection in near infrared (NIR) regime. (E) Photographs of a solid-like flexible IHN BCP PC on a black paper. Photo credit: H.S.K., Yonsei University.

  • Fig. 2 Structural and mechanical properties of IHN BCP PC.

    (A to C) Scattering intensity versus qz plots of IHN BCP PC films with different SCs of blue, green, and red, based on 2D GISAXS results in the insets. a.u., arbitrary unit. From left to right: Cross-sectional bright-field TEM images of IHN BCP PC films with different SCs of (D) blue (lamellae periodicity 151 nm), (E) green (lamellae periodicity 181 nm), and (F) red (lamellae periodicity 203 nm). From left to right: (G) Schematic illustration of nanoindentation experiment performed with the sequential loading, holding, and unloading. (H) Force-distance curves of the PS-b-P2VP and IHN BCP PC with red SC. (I) Effective moduli of a PS-b-P2VP, IHN BCP PCs with different SCs of blue, green, and red, and IHN BCP PCs with different amounts of EMITFSI. Effective modulus of a bare PEGDA hydrogel is also shown on the right side.

  • Fig. 3 Multiorder reflections of ionic liquid–doped IHN BCP PC.

    (A) UV-vis spectra of IHN BCP PC films on the glass substrates swollen with 5 wt % EMIMTFSI ink by varying spraying cycles. The films with their SCs arising from the first-order peaks in visible range since the second-order reflection appeared in the UV regime are denoted as group I. The films with their SCs in visible range arising dominantly from second-order reflection are denoted as group II. One with the SC in visible range from the mixing of second- and third-order reflection is denoted as group III. (B) Photographs of IHN BCP PC films corresponding to UV-vis spectra in (A). (C) FDTD-calculated stopband positions of IHN BCP PCs with various swelling ratios (α). α is defined by domain size of IHN-QP2VP divided by that of IHN-QP2VP with EMIMTFSI. The experimental results of (A) are also plotted with the simulated ones as a function of spraying cycle (solid symbols). (D) Representative FDTD simulation results of an IHN BCP PC at a swelling ratio of 2.4. First-, second-, and third-order peaks appear at 1107, 571, 385 nm, respectively. (E) Schematic of additive mixing of light. Photo credit: H.S.K., Yonsei University.

  • Fig. 4 Printable and rewritable SCs on IHN BCP PC.

    (A) Schematic of inkjet printing on IHN BCP PC film with ionic liquid (IL) ink. (B) Photograph of an IL ink-printed IHN BCP PC film with different concentrations. (C) Computer-processed image of the part of a one dollar bill in black and white contrast. (D) Photograph of the SC image printed by adjusting the concentration of the IL ink based on the contrast image in (C). (E) Optical microscope image of lines printed with IL on an IHN BCP PC film, which shows a resolution of the SC lines of approximately 50 μm. Photographs of IL ink-printed SC images of IHN BCP PCs on (F) a conventional paper and (G) glass substrate. (H) Photograph of an IL inkjet-printed image of an IHN BCP PC film arising from multiorder reflection SCs in visible range. (I) UV-vis spectra of an IHN BCP PC film printed with IL (red), followed by the removal of the IL by a neat PEGDA pad (black). (J) Maximum reflection wavelength values with repetitive IL writing and erasing processes. (K) Photographs of different IHN BCP SC images with repetitive printing and erasing of IL ink. An IHN BCP SC image (step 1) inkjet-printed with IL on an IHN BCP PC film, followed by removal of IL with a neat PEGDA pad. The printing and erasing process is repeatable (steps 2 and 3). Photo credit: H.S.K., Yonsei University.

  • Fig. 5 3D touchless BCP structural color sensing display.

    (A) Schematic illustration of humidity-sensitive SC change in an LiTFSI-doped IHN BCP PC. (B) Schematic of two-terminal parallel-type 3D touchless sensing display with an LiTFSI-doped IHN BCP PC. Height 1 (h1) is higher than height 2 (h2). (C) Variation of relative humidity as a function of the finger-to-PC distance. (D) Photographs of LiTFSI-doped IHN BCP PCs in various relative humidity conditions from 40 to 90 RH%. (E) Photograph showing SC of an LiTFSI-doped IHN BCP PC when a finger is close to the surface. (F) Capacitance change of a 3D touchless sensing display with an LiTFSI-doped IHN BCP PC upon variation of finger-to-PC distance from 15, 9, 5, and 3 mm. (G) Variation in capacitance of the 3D touchless sensing display upon repetitive alteration of the finger-to-PC distance. Schematic (H) and photograph (I) of arrays for 3D touchless sensing displays. (J) 3D capacitance change map obtained from the arrays of 3D touchless sensing displays with a finger close to the surface of the arrays. Photo credit: H.S.K., Yonsei University.

Supplementary Materials

  • Supplementary Materials

    3D touchless multiorder reflection structural color sensing display

    Han Sol Kang, Sang Won Han, Chanho Park, Seung Won Lee, Hongkyu Eoh, Jonghyeok Baek, Dong-Gap Shin, Tae Hyun Park, June Huh, Hyungsuk Lee, Dae-Eun Kim, Du Yeol Ryu, Edwin L. Thomas, Won-Gun Koh, Cheolmin Park

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