SnO2 Inverse Opal Composite Film with Low-Angle-Dependent

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SnO Inverse Opal Composite Film with Low Angle-dependent Structural Color and Enhanced Mechanical Strength Fangfang Liu, Bin Shan, Shufen Zhang, and Bingtao Tang Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b04053 • Publication Date (Web): 13 Mar 2018 Downloaded from http://pubs.acs.org on March 15, 2018

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SnO2 Inverse Opal Composite Film with Low Angle-dependent Structural Color and Enhanced Mechanical Strength Fangfang Liu1, Bin Shan2, Shufen Zhang1, Bingtao Tang1* 1

State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, PR

China 2

School of Environmental and Municipal Engineering, Qingdao University of Technology,

Qingdao 266033, PR China KEYWORDS: Direct template method; Low angle-dependent; Enhanced mechanical strength; Permanent structural color.

Abstract

Structural colors are attracting considerable attention for their advantages of environmental friendliness and resistance to fading. However, the weak mechanical strength and intrinsic iridescent color restrict their widespread application. This article describes a SnO2 inverse opal composite film with low angle-dependent structural color and enhanced mechanical strength. In

ACS Paragon Plus Environment

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the present study, a direct template method was used to prepare SnO2 inverse opals, which were then embedded in polydimethylsiloxane (PDMS). The structural colors of obtained composite films were low angle-dependent due to light scattering and high effective refractive index. Meanwhile, owing to the good physical strength of PDMS, structures of SnO2 inverse opals were provided with effective protection. No specific wavelength shift occurred during stretching, and exhibited excellent cycling stability. All these advantages indicated potential applications in packing and decorating materials.

Introduction Photonic crystals (PCs), especially inverse opals, are attracting considerable research attention for more extensive applications.1-5 Different from typical opal structure, inverse opals consist of an open, interconnected macropore structure and nanosized wall6 and are mainly fabricated by direct template method. This method first infiltrates precursor into opal templates and then remove templates.7-9 Based on it, numerous materials can be made into inverse opal to satisfy various applications. For example, Al-doped ZnO inverse opal has been introduced into a BiVO4 photoanode to improve the efficiency of solar water oxidation.10 Au-modified In2O3 inverse opals have been synthesized to detect acetone gas for diabetes diagnosis.11 Same as opals, visible light can be modulated by the periodic spatial structure, giving materials brilliant colors.12 Different from chemical colors, structural colors depend on physical structure instead of selective light absorbing, thereby protecting materials from photobleaching.13-18 And many researchers have focused on the study of angle-independent structural color.19-21 Kim et al. fabricated a novel photonic microgranules with low angle-dependent structural color.14 The selfhealable organogel nanocomposites were also endowed with angle-independent structural color


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by Yao et al, which can be applied in full-color displays.22 However, for some applications23-25 such as architecture, packing, decorating and security, their mechanical weakness causes the coloring structures are easily to be destroyed by external forces. To satisfy actual requirements, numerous scientists have attempted to improve the mechanical strength of PC materials.26-29 Wang et al. improved the mechanical robustness of PCs by infiltrating TiO2 and polydimethylsiloxane (PDMS) into voids of hollow SiO2.30 Particularly, many researchers have focused on endowing PC films with elasticity. Inomata et al. reported a structural colored elastomer with an interpenetrated polymer network (IPN) and colloidal particles immobilized by cross-linked poly (ethyl acrylate). Sensitive color change was induced by stretching deformation.31 Fudouzi et al. fabricated elastic silicone sheet by embedding colloidal particles in PDMS. The excellent properties of PDMS endowed composite materials with outstanding elastic tensile properties, allowing them to be stretched, bent, and compressed in various ways. Through cyclical rubber sheet stretching and releasing, the microsphere spacing of PCs varied and led to structural color change.32-33 The apparent tensile-dependent of structural color features potential application in detecting mechanical strain. However, some specific fields require enhanced mechanical strength while requiring the color to be free from stretch stimulus. Same as opal structure, the structures of inverse opals are destroyed easily because of their weak mechanical strength. In the present work, we fabricated SnO2 inverse opal /PDMS composite film with low angle-dependent structural color and enhanced mechanical strength. The structure of SnO2 inverse opal were consisted by small crystallites, which caused light scattering. Combined with enhanced effective refractive index, the composite films acquired low angle dependence. Meanwhile, the transparent elastomer PDMS possessed restoring force thus provided composite films with excellent mechanical property for repeated stretching and


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releasing. And, the colors were free from stretch stimulus. They have great potential to be applied in packing and decorating materials. Experimental Materials: Three sizes polystyrene nanoparticles (254, 316, and 371 nm) were prepared from emulsion polymerization30, the amount of emulsifier was 60mg, 35mg, and 15mg respectively. SnCl4·5H2O from XiLONG SCIENTIFIC was used for the preparation of three-dimensional ordered tin oxide colloidal crystals. The PDMS films were fabricated by Dow Corning Sylgard 184 silicone elastomer kit. Fabrication of SnO2 inverse opals: Direct template method was applied to fabricate SnO2 inverse opals. Polystyrene templates were close-packed in the fcc (face-centered cubic) arrangement through thermally assisted self-assemble.34 The SnO2 precursor was obtained by dissolving a certain amount of SnCl4·5H2O in ethanol. They were dropped from a corner to spontaneously infiltrate the entire template, and dry overnight. Afterwards, the samples were calcined in a muffle furnace with programmed temperature, 1°C /min to 100°C and hold for an hour, then with a heating rate of 2°C /min to 500°C, and cooled down naturally after maintaining 1h. To get inverse opal films in homogeneous color, the precursor should be enough to fill voids. Fabrication of elastic films: PDMS precursor was obtained by mixing silicone elastomer with curing agent at a weight ratio 10:1. They were cast on SnO2 inverse opal films and infiltrated into the voids at room temperature. After degassing sufficiently, they were put into an oven for solidification at 80 °C for half an hour. Finally, the elastic films with vivid color were peeled from the glass substrates.


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Characterization: Scanning electron microscopy (SEM, Nova NanoSEM 450) was used to measure the surface morphology after coating the samples with 20 nm thickness of gold. Transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), TEM energy dispersive X-ray spectroscopy (TEMEDX), and the selected area electron diffraction (SAED) pattern were all obtained from the FEI Tecnai transmission electron microscope. The powder X-ray diffraction (PXRD) pattern was obtained from a Panalytical Empyrean using Cu Kα radiation (λ = 1.5405 Å). Infrared spectroscopy was measured by Fourier transform infrared spectrograph Thermo Fisher 6700 and iN10. ESCALABTM 250Xi from Thermo Fisher was used for X-ray photoelectron spectroscopy (XPS). The reflectance spectra and diffuse scattering spectra were measured by the HITACHI U4100 spectrophotometer. The size of incident light source was 6 mm × 6 mm, the variable-angle accessory was applied at a scan speed of 300 nm/min with 8.00 nm slit width. The tensile property was measured by Precise PT-305 at 10mm/ min and although cycles for 50 times at 50mm/ min. The color variation during stretching was observed by the fiber optic spectrometer (EQ 2000) with incident and reflection angles fixed at 0 o under the cooperation of Precise PT305 at 10 mm/ min. Results and discussion Fabrication of the elastic structural color films As shown in Scheme 1, the direct template method35 was used to fabricate inverse opals: colloidal particles assembled into close-packing fcc arrangement, the target precursor infiltrated template voids, and the original template was removed. Then, the PDMS precursor infiltrated inverse opal. After solidification, the composite color film was peeled off from substrates. These


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films measured 0.6 mm thick and consisted of two layers: the inverse opal SnO2/PDMS composite layer (16–20 µm) and the bulk layer of pure PDMS. The thickness of SnO2/PDMS composite layer was determined by the thickness of inverse opal, which was directly controlled by the thickness of PS templates, and the overall thickness was determined by the amount of PDMS. Meanwhile, the abundant amount of SnO2 precursor was crucial to ensure the uniformity of colors (see Figure S1). The precursor cannot occupy the point contact part. With the calcining, the framework of inverse opal formed except for the connect part of PS spheres.

Scheme 1. Schematic of the process of fabricating PDMS films, and including inverse opal fabrication process. Three sizes (254, 316, and 371 nm) of PS nanospheres were fabricated by changing the emulsifier amount. The nanospheres initially assembled into a face-centered cubic (fcc) arrangement (see Figures 1a–1c) through thermally assisted self-assembly method. The next precursor-infiltration process exerted almost no influence on the structure of PS template (see Figure S1). After calcination, inverse opals formed identical arrangements in PS templates (see


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Figures 1d–1f), along with the volume shrinkage range from 31% to 36%. The pore sizes of inverse opals measured 163, 217, and 250 nm, and the average wall thickness was 26–28 nm. To verify the fcc arrangement, the 2D fast Fourier-transform (FFT) spectra of PS opals and SnO2 inverse opals are insert the upper right corner of Figure 1. After PDMS infiltration and solidification, structural colors of composite films were obtained, and they were relevant to the diameter of PS spheres obtained from source.

Figure 1. (a-c) SEM images of PS templates with diameters of 254 nm, 316 nm and 371nm. (d-f) SEM images of relevant SnO2 inverse opals with pore sized of 163nm, 217nm, and 250nm. FFT power spectra are inserted at the top right-hand corner of each figure. Figure 2 shows reflectance spectra of PS templates, SnO2 inverse opals, and composite film. They were measured through specular reflection mode with the incident fixed at 10°. Given the volume shrinkage and the change of materials nature, the peak positions of corresponding spectra


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presented a strong shift (see Table S1). The wavelength peak positions of composite films reached 448, 567, and 656 nm and corresponded to blue, green, and red colors, respectively.

Figure 2. The reflection spectra of corresponding sample measured by HITACHI U-4100 spectrophotometer in specular reflection mode. (a) PS templates (b) SnO2 inverse opal (c) inverse opal SnO2/PDMS composite film. The lines in same color are corresponding to each other. These composite films were easily peeled off from substrates and inverse opals barely remained on the substrate. The interconnected pores (see Figure 3a) created a convenient condition for PDMS precursor to full filling them spontaneously (see Figure S2). Furthermore, high-resolution transmission electron microscopy (HRTEM) of pure inverse opal was obtained and illustrated that the rough walls of inverse opals were composed of small crystallites (see Figure 3b). The representative lattice fringe spacing was 3.34 Å and coincided with the tetragonal (110) facet of SnO2 crystal form (see Figure S3). To confirm that SnO2 inverse opals were completely coated by PDMS, TEM and TEM energy-dispersive X-ray spectroscopy (TEMEDX) of composite film were carried out after ultramicrocutting (see Figures 3c–3d). Meanwhile, different element distributions in the composite film were also detected by EDX elemental mapping (see Figure 3e). Distribution area of each elements fit perfectly with the


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HAADF-STEM images. Si-K and C-K were distributed around Sn, intuitively demonstrating that PDMS completely covered inverse opal. The above-mentioned coating structures were further examined by infrared spectrum (see Figure 4a). Spectrum of the back of composite film was the same as that of pure PDMS, whereas both significantly differed from that of SnO2. More importantly, no SnO2 peak was identified in the back of composite film.


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Figure 3. (a-b) TEM and HRTEM image of SnO2 inverse opal, (c-d) TEM image of the composite film, (e) HAADF-STEM image and EDX elemental mappings of Sn-L, Sn-K, Si-K, C-K in composite film. The coating structure were further characterized by X-ray photoelectron spectroscopy (XPS). Two typical peaks of Sn 3d were observed in SnO2, whereas no remarkable peak was detected at the back of PDMS color film (see Figure 4b). The peak of Sn 3d in the composite film approached that of machine noise because it was completely wrapped by PDMS (see Figure S4). O 1s in the back of composite film was the same as that of pure PDMS and distinct from that of SnO2 (see Figure 4c). The signals of Sn 3d and O 1s in SnO2 inverse opal were both shielded by PDMS. These results provided strong evidence that SnO2 inverse opals were completely covered. Thus, PDMS played an important role in securing and protecting inverse opal structure from its physical

weakness.

Figure 4. (a) Infrared spectroscopy of the free-standing film and SnO2 inverse opal (b-c) XPS spectrum of Sn and O in SnO2, PDMS and composite film. Optical properties of the structural color films


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Figures 5a–5c show the diffuse scattering spectra of elastic films measured under the detection angle ranging from 10 o to 40 o with the incident angle fixed at 0 o, for it can reflect structural colors veritably as in the natural environment and was widely used by many researchers.36-38 The incident angle was fixed perpendicular to the film surface with detection angles from 10° to 40° (see Figure 5e). Evidently, the peak position of scattering spectra changed infinitesimally with detection angle ranging from 10° to 40°, blue shift for each color film measured 13, 16, and 16 nm (see Figure 5d). Comparing the optical photographs obtained at 10° and 40°, colors almost remained constant exhibiting low angle-dependent (see Figure 5f).

Figure 5. (a-c) The diffuse scattering spectra of three color films under the detection angle ranging from 10

o

to 40

o

with the incident angle fixed at 0 o. (d) the peak position of the

scattering spectra under different detection angles. (e) the description of diffuse scattering mode.


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(f) optical photograph of blue, green, and red elastic films with the shooting angle of 10 ° and 40 °. The illuminant for optical photos was LED lamp. The size of each film is 20 mm × 20 mm. Inverse opal SnO2/PDMS composite film possessed an orderly structure, and vivid colors were derived based on Bragg diffraction (see Formula S4).39 The effective refractive index neff can be estimated according to Formula (1). ଶ ଶ ݊ୣ୤୤ = ටƒୗ୬୓మ · ݊ୗ୬୓ + ƒ୔ୈ୑ୗ ݊୔ୈ୑ୗ మ

(1)

For opals, the volume fraction ƒ of spheres and air are 74% and 26%, respectively. However, for inverse opals the volume fraction of SnO2 framework exceeded 0.26. Instead of connecting with one another point to point similar to PS spheres, air spheres were partitioned by SnO2 framework (see Figures 1d–1f). To further understand ƒ for SnO2 framework and PDMS infiltration into holes, the simplified diagram based on the SEM image of inverse opals is shown in Figure S5. The calculated volume fractions for each section are shown in Table S2. Combining Formula (1) and Figure S5, neff for inverse opal SnO2/PDMS composite film was between 1.59 and 1.75. Based on Bragg diffraction (see Formula S4), improving the effective refractive index can effectively diminish the influence of angle. Comparing the composite film with pure SnO2 inverse opal (see Figure S6), the blue shift for SnO2 inverse opal measured 38 nm. As the refractive index of PDMS is higher than that of air, filling PDMS into voids has improved effective refractive index and this increment lead to a decline in angle dependence. Additionally, light scattering originating from the structure of inverse opal is another pivotal factor in cutting down angle dependence degree.15,36,40-42 Taking PS template into account, whose blue shift was


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66 nm (see Figure S6), the angle dependence of SnO2 inverse opal was lower although the effective refractive index of PS was higher. On account of small crystallites of inverse opal structures (see Figures 3a–3b), the surface of inverse opal was rough. And the scattering originating from it widened the viewing angle.43-44 Therefore, angle dependence for inverse opal has been effectively reduced. Based on the above two factors, the composite films exhibited low angle dependence. Mechanical properties Aside from low angle dependence, another important phenomenon was noticed. Upon stretching, wavelength peak position of composite films was invariable along with descending reflectance (see Figures 6a–6c). Wavelength peaks at different strain levels remained unchanged. As shown in Figure 6d, unlike PDMS films embedded with colloidal particles,19, 29 the skeleton of SnO2 inverse opals broke into pieces due to the pull force caused by stretching. Gaps between inverse opals pieces were enlarged by the drag of PDMS ligament (see Figure S7). However, the pieces maintained an ordered structure and the same pore sizes as before. According to Bragg’s law (see Formula S4), d and neff were not changed, thus keeping the band gaps invariant. As reflected on optical photos (see Figure 6e), color was invariant along with drop-in vividness. It is needed to point out that the inverse opal SnO2/PDMS composite layer was the color source, meanwhile the bulk layer of pure PDMS played the main role of improving mechanical property. Owing to high degree of transparency of PDMS, pure PDMS layer posed no effect on color. Figure 6g shows the complete stretching curve of PDMS film. Stress increased with increased strain until the film broke. Peak tension measured 13.67 N, tensile strength was 2278.4 kPa, tensile strain totaled 154%, and peak tensile strain was 154%. They were also endowed with excellent cycle performance and loop curves were well matched for fifty cycles of stretching and


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releasing (see Figure 6h). Meanwhile, color was still present without any shift in wavelength peak after multiple cycles (see Figure 6i). In addition to excellent tensile properties, PDMS composite film can be considered flexible for it can be casually twisted and bent (see Figure 6f). Notably, introduction of PDMS has achieved strength enhancement and provided protection of inverse opals structure. Thus, the proposed method can ensure permanent structural color of materials.


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Figure 6. (a-c) The reflection spectra of three color films at different strain levels, and the data were processed by normalization. They are corresponding to blue, green, and red, respectively. (d) schematic of the stretching process. (e) optical photo of green composite film at several critical moments during the stretching process, which is associated with (b). (f) photograph of three color films taken in the case of bending. (g) the complete tensile curve for PDMS film until it interrupts (h) the tensile cycle curve for 50 times at the stretching velocity of 50mm/min (i) the peak position of the reflection spectra at the release state for 50 times cycle. Conclusions A composite film with two layers, inverse opal SnO2/PDMS composite layer and the bulk layer of pure PDMS layer, was successfully fabricated by embedding SnO2 inverse opal with PDMS. Fcc arrangement of PS templates was maintained throughout even in the composite film. By tuning sphere size and considering volume shrinkage, three colored composite films were obtained. Given the thickness of inverse opal framework, the volume fraction differed from that of opals. Combined with theoretical calculation of effective refractive index, the established model was reasonable and provided a method for calculating effective refractive index of other materials. Given the light scattering and high effective refractive index, structural color of the composite film was low angle-dependent. Meanwhile, the composite films were provided with outstanding mechanical property for repeated stretching and releasing. During stretching, structural color was invariable and did not result in color fading. The prepared materials can be potentially applied in packing and decorating materials. ASSOCIATED CONTENT Supporting Information.


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The Supporting Information is available free of charge on the ACS Publications website. Some essential information such as figures, tables and the explanation of effective refractive index are shown in Supporting Information. AUTHOR INFORMATION Corresponding Author *[email protected] Acknowledgment This work was supported by the National Natural Science Foundation of China (21276042, 21576039, 21536002, 21421005 and U1608223), Program for Innovative Research Team in University (IRT_13R06). References (1)

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(20) Zhang, C.; Wu, B.; Du, Y.; Ma, M.; Xu, Z. Mussel-inspired Polydopamine Coatings for Large-scale and Angle-independent Structural Colors. J. Mater. Chem. C. 2017, 5, 3898–3902. (21) Chung, K.; Y, S.; Heo, C.; Shim, J, W.; Yang, S.; Han, M, Gyu.; Lee, H.; Jin, Y.; Lee, S, Y.; Park, N.; Shin, Jung, H. Flexible, Angle-Independent, Structural Color Reflectors Inspired by Morpho Butterfly Wings. Adv. Mater. 2012, 24, 2375–2379. (22) Zhou, J.; Han, P.; Liu, M.; Zhou, H.; Zhang, Y.; Jiang, J.; Liu, P.; Wei, Y.; Song, Y.; Yao, X. Self-Healable Organogel Nanocomposite with Angle-Independent Structural Colors. Angew. Chem. 2017, 129, 10598–10602. (23) Ge, D.; Lee, E.; Yang, L.; Cho, Y.; Li, M.; Gianola, D. S.; Yang, S. A Robust Smart Window: Reversibly Switching from High Transparency to Angle-Independent Structural Color Display. Adv. Mater. 2015, 27, 2489−2495. (24) Wu, S.; Liu, B.; Su, X.; Zhang, S. Structural Color Patterns on Paper Fabricated by Inkjet Printer and their Application in Anticounterfeiting. J. Phys. Chem. Lett. 2017, 8, 2835−2841. (25) Zhong, K.; Liu, L.; Lin, J.; Li, J.; Cleuvenbergen, S. v.; Brullot, W.; Bloemen, M.; Song, K.; Clays, K. Bioinspired Robust Sealed Colloidal Photonic Crystals of Hollow Microspheres for Excellent Repellency Against Liquid Infiltration and Ultrastable Photonic Band Gap. Adv. Mater. Interfaces. 2016, 3, 1600579. (26) Meng, Y.; Tang, B.; Cui, J.; Wu, S.; Ju, B.; Zhang, S. Biomimetic Construction of Non-Iridescent Structural Color Films with High Hydrophobicity and Good Mechanical Stability Induced by Chaotic Convective Coassembly Method. Adv. Mater. Interfaces. 2016, 3, 1600374.


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(27) Wang, F.; Zhang, X.; Lin, Y.; Wang, L.; Zhu, J. Structural Coloration Pigments Based on Carbon Modified ZnS@SiO2 Nanospheres with Low-Angle Dependence, High Color Saturation, and Enhanced Stability. ACS Appl. Mater. Interfaces. 2016, 8, 5009−5016. (28) Meng, Y.; Tang, B.; Xiu, J.; Zheng, X.; Ma, W.; Ju, B.; Zhang, S. Simple Fabrication of Colloidal Crystal Structural Color Films with Good Mechanical Stability and High Hydrophobicity. Dyes and Pigments. 2015, 123, 420−426. (29) Meng, Y.; Tang, B.; Ju, B.; Wu, S.; Zhang, S. Multiple Colors Output on Voile through 3D Colloidal Crystals with Robust Mechanical Properties. ACS Appl. Mater. Interfaces. 2017, 9, 3024−3029. (30) Zhang, X.; Wang, F.; Wang, L.; Lin, Y.; Zhu, J. Designing Composite Films of SiO2/TiO2/PDMS with Long Lasting Invariable Colors and Enhanced Mechanical Robustness. Dyes and Pigments. 2017, 138, 182−189. (31) Ito, T.; Katsura, C.; Sugimoto, H.; Nakanishi, E.; Inomata, K. Strain-Responsive Structural Colored Elastomers by Fixing Colloidal Crystal Assembly. Langmuir. 2013, 29, 13951−13957. (32) Xu, H.; Yu, C.; Wang, S.; Malyarchuk, V.; Xie, T.; Rogers, J. A. Deformable, Programmable, and Shape-Memorizing Micro-Optics. Adv. Funct. Mater. 2013, 23, 3299−3306. (33) Fudouzi, H.; Sawada, T. Photonic Rubber Sheets with Tunable Color by Elastic Deformation. Langmuir. 2006, 22, 1365−1368. (34) Liu, F.; Xiu, J.; Tang, B.; Zhao, D.; Zhang, S. Dynamic Monitoring of Thermally Assisted Assembly of Colloidal Crystals. J. Mater. Sci. 2017, 52, 7883−7892.


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Green

Light-emitting

Diodes

with

Nano-rough

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Surface

using

Nanoimprint

Lithography. Nanotechnology. 2008, 19, 185301. (44) Miyake, M; Chen, Y; Braun, P, V; Wiltzius, P. Fabrication of Three-Dimensional Photonic Crystals Using Multibeam Interference Lithography and Electrodeposition. Adv. Mater. 2009, 21, 3012–3015.


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For Table of Contents Use Only


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Scheme 1. Schematic of the process of fabricating PDMS films, and including inverse opal fabrication process. 73x31mm (300 x 300 DPI)


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Figure 1. (a-c) SEM images of PS templates with diameters of 254 nm, 316 nm and 371nm. (d-f) SEM images of relevant SnO2 inverse opals with pore sized of 163nm, 217nm, and 250nm. FFT power spectra are inserted at the top right-hand corner of each figure. 94x52mm (300 x 300 DPI)


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Figure 2. The reflection spectra of corresponding sample measured by HITACHI U-4100 spectrophotometer in specular reflection mode. (a) PS templates (b) SnO2 inverse opal (c) inverse opal SnO2/PDMS composite film. The lines in same color are corresponding to each other. 47x13mm (300 x 300 DPI)


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Figure 3. (a-b) TEM and HRTEM image of SnO2 inverse opal, (c-d) TEM image of the composite film, (e) HAADF-STEM image and EDX elemental mappings of Sn-L, Sn-K, Si-K, C-K in composite film. 149x130mm (300 x 300 DPI)


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Figure 4. (a) Infrared spectroscopy of the free-standing film and SnO2 inverse opal (b-c) XPS spectrum of Sn and O in SnO2, PDMS and composite film. 50x15mm (300 x 300 DPI)


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Figure 5. (a-c) The diffuse scattering spectra of three color films under the detection angle ranging from 10 ° to 40 ° with the incident angle fixed at 0 °. (d) the peak position of the scattering spectra under different detection angles. (e) the description of diffuse scattering mode. (f) optical photograph of blue, green, and red elastic films with the shooting angle of 10 ° and 40 °. The illuminant for optical photos was LED lamp. The size of each film is 20 mm × 20 mm. 106x66mm (300 x 300 DPI)


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Figure 6. (a-c) The reflection spectra of three color films at different strain levels, and the data were processed by normalization. They are corresponding to blue, green, and red, respectively. (d) schematic of the stretching process. (e) optical photo of green composite film at several critical moments during the stretching process, which is associated with (b).(f) photograph of three color films taken in the case of bending. (g) the complete tensile curve for PDMS film until it interrupts (h) the tensile cycle curve for 50 times at the stretching velocity of 50mm/min (i) the peak position of the reflection spectra at the release state for 50 times cycle. 168x166mm (300 x 300 DPI)


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SnO2 Inverse Opal Composite Film with Low-Angle-Dependent

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