Supporting Information

Transcription

1 Supporting Information Free-Standing Photonic Crystal Films with Gradient Structural Colors Haibo Ding, Cihui Liu, Baofen Ye, Fanfan Fu, Huan Wang, Yuanjin Zhao*, Zhongze Gu* State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing , China; S-1

2 Methods Fabrication of PhC hydrogel films. Monodisperse silica nanoparticles with diameters of 125 nm were synthesized by the Stober-Fink-Bohn method. Poly(ethylene glycol) diacrylate (PEGDA, M w = 700) and polyethylene glycol (PEG, M w = 200) were purchased from Alfa Aesar China Ltd. 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP) was obtained from Sigma (St Louis, MO). The colloidal silica nanoparticles were purified via centrifugation. Then, the purified colloidal nanoparticles were dispersed in deionized water and added with an excess of ion-exchange resin (Bio-Rad, AG501-X8(D)). The pre-gel solution was composed of PEGDA (10%, v/v), PEG (5%, v/v), HMPP (1%, v/v), and the above colloidal crystal array solution. In a typical experiment, 10% (v/v) ion-exchange resin was added to the pre-gel solution. After extensive mixing, the pre-gel solution was sonicated for 1 h to form iridescent colors. The ion-exchange resin was removed by centrifuge. A mold was prepared with two flat glass slides separated by a spacer (250 µm in thickness). The pre-gel solution was introduced into mold, and then exposed to 365 nm UV light (EXFO OmniCure 1000) for 10s. After the structure of the colloidal crystal stabilized, the mold was removed and the film could be cut into a rectangle shape by a blade. Fabrication of free-standing PhC films. 2-hydroxyethyl methacrylate (HEMA) and ethyleneglycol dimethacrylate (EGDMA) were obtained from Sigma (St Louis, MO). The achieved PEGDA film was immersed in absolute ethyl alcohol for three times and each time lasted for 30 minutes. Then, the PEGDA film was immersed in the pre-gel solution of a photosensitive resin and ethanol was selectively evaporated for 12 h at 60 C. The pre-gel solution for the second polymerization was composed of HEMA (98%, v/v), EGDMA (1%, v/v), and HMPP (1%, v/v). After UV exposure for 20 s, the robust film with brilliant structure colors was generated. Fabrication of free-standing PhC films with continuous colors. A fixture was prepared with two slides (76.2 mm in length, 25.4 mm in width, and 1.2 mm in thickness), a glass fiber (3mm in length and 250 µm in diameter) and a binder clip. S-2

3 The fiber was fixed between the slides to act as the spacer and the binder clip was used to clamp the slides at the other side. The colloidal crystal film was placed in the fixture and its thickness was changed with the gap between the two slides. The PBG range and slop of the film could be tuned by adjusting the distance between the spacer and the binder clip. Before the second polymerization, the PEGDA film with the infiltration of HEMA monomer was placed in the specialized fixture. After UV irradiation, the film was removed from the fixture. Fabrication of PhC films with circular symmetry microstructures. The glass fibers were purchased from Beijing glass research institute and polydimethylsiloxane elastomer kits (PDMS, Sylgard 184) were purchased from Dow Corning. The glass fibers were cut into 30 mm and arranged side by side on a glass slide. The mixture of PDMS and its harder was 5:1. After complete mixing, the PDMS resin was poured on the aligned glass fibers and cured for 4 h at 80 C. Then the PEGDA pre-gel suspension was introduced into the PDMS antitemplate, following by a UV irradiation. Characterization. Photographs of the colloidal crystal suspensions and PhC films with structural colors were obtained with a digital camera (Canon, EOS 5D Mark II). The reflection spectra of the suspensions and film were measured using an optical spectrometer (Ocean Optics, USB 2000) and a tungsten halogen source (Ocean Optics, LS-1). The microstructures of the PhC film were obtained with a field emission SEM (Zeiss, Ultra Plus). Optical images of the glass fiber templates and PDMS antiplates were taken by a stereo microscope (Olympus, MVX10) equipped with a CCD camera (Media Cybernetics Evolution MP 5.0). To characterize the film from different observing angles, schematic illustration of the experimental setup is shown in Figure S2. S-3

4 Supporting Figures: Figure S1 (a-d) Scanning electron microscopy images of the surfaces at positions corresponding to Figure 4 (c-f), respectively. Figure S2 Schematic illustration of the viewing angle in the experimental setup. When the spectrometer or camera is fixed and the light source is varying, the color keeps stable for the films with circular symmetry structures. Meanwhile, there is angle dependence for the colors of the normal flat PC film. S-4

5 Figure S3 Cross-sectional optical image of the circular symmetry microstructures on the PhC films. S-5