Soft Display Using Photonic Crystals on Dielectric Elastomers - ACS

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Applications of Polymer, Composite, and Coating Materials

Soft Display Using Photonic Crystals on Dielectric Elastomers Tenghao Yin, Tonghao Wu, Danming Zhong, Junjie Liu, Xiangjiang Liu, Zilong Han, Honghui Yu, and Shaoxing Qu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b05451 • Publication Date (Web): 03 Jul 2018 Downloaded from http://pubs.acs.org on July 6, 2018

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ACS Applied Materials & Interfaces

Soft Display Using Photonic Crystals on Dielectric Elastomers Tenghao Yin a, Tonghao Wu a, Danming Zhong a, Junjie Liu a, Xiangjiang Liu b, Zilong Han a , Honghui Yu c, and Shaoxing Qu*,a a. State Key Laboratory of Fluid Power & Mechatronic System, Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Department of Engineering Mechanics, Zhejiang University, Hangzhou 310027, China b. College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China c. Department of Mechanical Engineering,The City College of New York,New York, NY 10031, USA * Corresponding author: [email protected] Keywords

soft display, photonic crystal, dielectric elastomer, chromatic, robustness

Abstract Soft display has been intensively studied in recent years in the wake of rapid development of a variety of soft materials. The current existing solutions for translating the traditional hard display into the more convenient soft display mainly include LEDs, liquid crystals, quantum dots and phosphors. The desired soft display should take the advantages of facile fabrication processes and cheap raw materials. Besides, the device should be colorful, nontoxic and not only flexible but also

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stretchable. However, the foregoing devices may not own all the desired features. Here, a new type of soft display, which consists dielectric elastomer and photonic crystals that covers all the features mentioned above and can achieve the color change dynamically and in situ, is reported. In addition to the above features, the angle-dependent characteristic and the excellent mechanical reliability make it a great candidate for the next generation of soft display. Finally, the vast applications of the present concept in varieties of fields are also prospected.

1.

Introduction

In recent years, soft display has attracted more and more attentions due to its flexibility, portability and even chromatic color. To achieve this goal, various approaches are attempted, including inorganic1-2/organic3-5/polymer6-7 light emitting diode (LED), liquid crystals8, quantum dot9 and phosphor10. However, these devices are either technically difficult to make or totally monochromatic in certain states or devices. For example, the liquid crystals are mostly toxic and synthetically complex. The LEDs and phosphor can only emit one color once the device is completed, and the quantum dot has relatively low yield and inevitable fluorescence quenching when aggregated. These drawbacks severely limit their applications and popularization. On the other hand, photonic crystals (PCs) are getting more and more popular in the last two decades due to their unique structural color. In this respect, various devices have been proposed in different applications such as sensors11-12, biological detection13, light path devices14, disguise15, anti-counterfeiting16, and photonic

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papers17-18. The applications discussed above can all be attributed to the change of structural color of PCs under external stimuli. To this end, lots of scholars proposed the idea of using PCs to achieve color display. In summary, these devices can be categorized as electric-19-20, magnetic-21, pressure-22, moisture-23, and thermal-24 controlled by their modulating methods. Mostly, the working environment of photonic materials for display is solid-state. For instance, Ozin et al. reported a full-color display based on 3D well-ordered multilayer photonic crystals to display the entire range of visible light25, as well as the inverse opal crystals26. However, 3D PCs is not as cost-effective as 2D PCs and the electrode they used is ITO glass, whose rigidity limits its popularization in soft or wearable electronics. In respect to the soft materials, dielectric elastomers (DEs) have been widely investigated due to its high efficiency, light weight, large deformability, and fast response. A typical DE actuator27-29 is usually a sandwiched structure with the electrodes on the two surfaces of the DE membrane. When a voltage is applied, the film undergoes an in-plane deformation. This character can be used to adjust the structural color of PCs. In this work, we propose a new and straightforward method to realize the in-situ soft color display. This is achieved by an electric sandwiched structure incorporating with 2D PCs. Transparent gels are used as the electrodes. When external voltage applied over the selected electrodes, colorful geometrical pattern can be easily observed from the “soft screen”. Scattering spectrum was performed to reveal the angle-dependence of the device. An analytical model was then used to explain the 3



polychrome phenomenon qualitatively. Finally, we demonstrated the reliability and robustness of the device. Our device can cover the whole range of the visible lights and can still hold after a mass of abusement which is much more suitable for the next generation soft display. Though there are a few devices utilizing the combining PCs and DEs

[21]

, to our best knowledge, this is the first time of using it for the

electric-actuated soft display and we believe it can inspire the designing and fabrication of more complex optical devices for soft and colorful display in the not-too-distant future.

2.

Results

2.1. Fabrication of soft display

The fabrication of the soft color device is illustrated in Figure 1a. The acrylic sheet was firstly engraved into two square frames with inner and outer side lengths of 50mm and 70mm respectively with the help of a laser cutting machine (VLS2.30, Universal Laser System. Inc). A DE film (VHB 4905, 3M) with the initial thickness 0.5mm was then pre-stretched equal-biaxially at a stretch λ = 3 (Figure 1a, i) and put between the two rigid frames (Figure 1a, ii). Next, with the help of MPI method (Figure 1a, iii, see details in Experimental Section), the prepared monodispersed polystyrene (PS) particles, with diameters in hundreds of nanometers, were injected onto the pre-stretched film. After this step, a 2D well-ordered close-packed monolayer of particles was self-assembled and attached on the top surface of the film due to the viscidity of the film (Figure 1a, iv). Finally, transparent gel electrodes were smeared 4


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onto the two sides of the film (Figure 1a, v), following the pattern pre-designed on a mask. When a voltage is applied over the selected electrodes, the pre-stretched film undergoes patterned in-plane deformation due to the Maxwell stress, which enlarges the lattice of the 2D PCs and shows the designed patterns (Figure 1a, vi). Figure 1b shows the scanning electron microscope (SEM) image of the 2D PCs in step (iv) of Figure 1a. The close-packed hexagonal lattice can be clearly seen in this figure. The small space between the neighboring particles result from the manufactural procedure during the SEM characterization, i.e. the film was further stretched slightly when pasted on the platform. Apparently, the particle size is homogeneous, which contributes to the later excellent display results. The resultant device is soft in the central area and rigid at the edges, which gives the device the ability of changing color and the high robustness, respectively. A white light source illuminates the device at an angle of α with respect to the surface normal and a CMOS camera (Nikon D7200, Japan) captures the scattering light at the other side, at an angle of β with respect to the same normal (Figure 1c, note that β is counted from the normal at the incident side, we denote the angle of CMOS camera as 180°-β in this figure). These angles are defined by the central point of the display.

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Figure 1. Illustration of the soft display device. (a) Fabrication processes of the soft display device, including the pre-stretch (i, ii), injection of the particles and the assembly of 2D PCs (iii, iv), adding the patterned electrodes (v) and applying voltage (vi). (b) SEM image of the 2D PCs shows that the PS particles were well-ordered with close-packed hexagonal lattice. (scale bar 3μm) (c) Experimental setup with the light source and CMOS camera on the two sides of the device. (d) The device can display the alphabets (the first column), numbers (the second column), and pixels (the third column). When the voltage increases from 0.0kV to 3.0kV (from the first to the last row of this figure), the color changes from blue to green then to red.

Our device can display almost all the patterns that we want due to the steps (v) and (vi) in Figure 1a. In step (v), we use a mask to obtain patterned transparent gel 6


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electrodes on the surfaces of the film. Furthermore, we can control the “voltage on” or “voltage off” state of each pair of electrodes independently in step (vi). By setting α about 45° and β=180° in the experiments, we use the device to display alphabets, numbers and even the selected pixels as shown in Figure 1d. In all the pictures, the background color is blue which locates on the very left side of our visible light spectrum. As shown in the first row of Figure 1d, when the voltage is zero, the patterned area shows the same blue as the surrounding background. As the voltage increases, the color turns to green (volt=2.6kV) and finally red (volt=3.0kV), during which the color contrast between the patterned area and the background also increases. It’s not mono-colored in each pixel because of two main reasons: (1) the light source of the device is not strictly parallel light, resulting in the difference of incident angle in each point of the pixel, and (2) the strain is in fact non-uniform in the rectangular region, resulting in the difference of lattice constant of the photonic crystals. The weight of the nanoparticles is negligible hence doesn’t affect the stiffness of VHB. The gel electrodes are not cross-linked with a thickness about 150µm and can be conformal with the film during the deformation. Based on this, the effect of the gel electrode on the stiffness of the VHB is also assumed to be negligible. It’s worth noting that this voltage driven change is instant and in situ. It is really a different mechanism compared with the previous soft displays discussed in the Introduction, none of which possesses this feature. Besides, the fabrication of the present device is straightforward and nontoxic. The raw materials used are low cost and easy to obtain.

2.2. Angle-dependent characteristics 7



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To further study the 2D photonic device, we investigate the spectrum characteristics of this 2D photonic device under “off” and “on” states of voltage as shown in Figure 2 and Figure 3, respectively. In Figure 2a-c, the incident angle α is fixed as 30°, 45° and 60°, the viewing angle ranges from 135° to 185° with an increment of 5°. It can be clearly seen that for a fixed incident angle, the peak wavelength of the scattering spectrum undergoes a blue-shift when the viewing angle (defined by β, Figure 1c) increases. Besides, at the fixed viewing angle (β=160°), the peak wavelength shows a red-shift tendency when the incident angle decreases as shown in Figure 2d. This soft photonic device can display the whole visible light range. This can be interpreted by our theoretical model as depicted in Figure 2e. In this model, the optical diffraction is regarded as Bragg-like reflection. Here, α and β are the incident angle and observation angle respectively, and d is the lattice constant of the 2D PCs. Path difference of two parallel waves is x1 at the incident side of the film and x2 at the observation side. From geometric relation, x1 = d sin α , x2 = d cos ( β − 90o ) = d sin β

(1)

Due to light interference, the light intensity is a peak when the total path difference between the two waves is the integer multiples of the incident wavelength, that is

x1 + x2 = mλ

(2)

where m is an integer and λ is the central wavelength. Substituting Equation 1 into Equation 2, we have

x1 + x2 = d ( sin α + sin β ) = mλ 8


(3)

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For three different α, the peak wavelength calculated from Equation 3 was plotted as a function of viewing angle (right vertical axis) in Figure 2a-c, represented by the dashed line and black triangle symbols. It can be seen that the peak wavelengths obtained from Equation 3 are in agreement with the experimental results for all the incident and viewing angles tested.

Figure 2. Spectrum characteristics of the device without external voltage. (a-c) Scattering spectrums at different viewing angles for three incident angles: (a) α=30° (b) α=45° and (c) α=60°. The dashed lines with black triangle symbols give the relation between the peak wavelength and the viewing angle (right vertical axis) calculated from Equation 3. The theoretical results agree well with the experiments.

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(d) Scattering spectrums at the fixed observation angle β=160° for incident angles α=60° (top), α=45° (middle) and α=30° (down). The peak wavelength red shifts as the incident angle decreases. (e) Theoretical model of the device. and indicated at the two sides of the membrane, are the differences in the traveling distance for two parallel waves. Constructive interference occurs when the total path difference is the multiples of the incident wavelength. Spectrum plots in this figure are smoothed by Savitzky-Golay method.

The voltage-controlled characteristics were also investigated both experimentally and theoretically. We are interested in the center pixel of a “5×5” pixelated pattern. In detail, we performed three sets of experiments with incident/viewing angles being 30° /150° , 45° /170° , and 60° /180° respectively. In each experiment, we adjusted the applied voltage from 0V to 2.8kV gradually while kept the incident angle and the viewing angle fixed. When applied a voltage, the film contracts in the thickness direction due to the Maxwell stress and expands in area. As the applied voltage increases, the affected area of the membrane expands more in the in-plane directions, causing the increase of the lattice constant of the 2D PCs. That is, the value d in Equation (3) increases with voltage. Thus, the peak wavelength also moves up according to Equation (3). This red-shift of peak wavelength is clearly shown in Figure 3a-c. Besides, the intensity of the transmitted light also increases due to the decrease in thickness of the membrane and the increase of the spacing among the particles of the PCs. We used the circular actuator model from our previous work30 to calculate the change of the lattice constant(details listed in Supporting Information).

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Combining the circular actuator model with Equation 3, we predicted the peak wavelength as a function of the voltage for the specified incident/viewing angles. The theoretical results are plotted in Figure 3a-c in dashed lines with black triangle symbols, the right vertical axis gives the voltage. When the voltage is zero, this model agrees well with all the experimental results except a little deviation caused by the transparent electrodes. However, when the voltage increases to 2.0kV, the predicted peak wavelength is larger than the experimental result. This could be ascribed to the viscoelasticity of the film, since the film may not be able to deform fully to the predicted value when the voltage first jumps from 0 to 2.0kV, giving the loading rate higher than that used in the characterization of the elastic behavior. This effect becomes less significant in the later experiments, when the voltage increases 0.2kV each time, giving the membrane more time to further deform which might be close to the state used in material characterization.

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Figure 3. Spectrum characteristics of the device with external voltage. (a-c) Scattering spectrums

under different voltages for three fixed pairs of incident and viewing angles: (a) α=30°, β=150° (b) α=45°, β=170° and (c) α=60°, β=180°. The dashed lines with black triangle symbols give the relation between the peak wavelength and the applied voltage (right vertical axis), calculated from the combination of the circular actuator model (details in Supporting Information) and Equation 3. The theoretical results are slightly larger than the experiments due to the viscoelasticity of the film. (d) Theoretically peak wavelength as a function of applied voltage for incident angle α=45° (blue area dominates), α=60° (green area dominates) and α=75° (red area dominates). This figure reveals that

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the peak wavelength can cover the range of the whole visible light by adjusting the applied voltage. The efficient actuation region is dyed in dark grey. (e) Photograph of the experimental setup. Colorful patterns can be seen at the angle β=180°, but it totally turns into white when β deviates from this angle. Spectrum plots in this figure are smoothed by Savitzky-Golay method.

Additionally, we predicted the peak wavelength-voltage relation at the fixed viewing angle of β=180° for three different incident angles α=45°, α=60°, and α=75°. As shown in Figure 3d, when the incident angle is relatively small (α=45°), the short wavelength (in the blue region) dominates. For the other two larger incident angles (α=60° and α=75°), green and red dominates, respectively. This calculation shows that we can use our present model for full-color display: the device can display the whole visible spectrum by adjusting the incident angle and the applied voltage. What’s more, we can see that the most effective change of the wavelength is mostly located in the dark grey area in Figure 3d, when the voltage changes from 2.0kV to 3.0kV. This is due to the nonlinear strain-voltage relation of DE. The change in light intensity for different viewing angles or material strain can be attributed to many aspects, such as the non-uniform distribution of wavelength in the incident light, the interaction between the incident light and the nanoparticles and the quantum effect, which is a very sophisticated mechanism. However, the final intensity remains the same at the points that locating on the same latitude, since it is a superposition of the scattering intensities of different incident lights. In other words, the real color is the combination of these waves and the perceived color is mainly

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determined by the intensity of the peak wavelength and the bandwidth. The spectrum of the received lights also depends on the viewing angle. As shown in Figure 3e, color pattern of the display can be seen at the viewing angle β=180°. However, the display is totally white and colorless when viewed at an angle about β=200°. This might be beneficial to protect our privacy in certain applications.

2.3. Fatigue tests

Figure 4. Fatigue tests of the device. (a) The step-voltage with amplitude 2.6kV and frequency 1Hz

applied on the device. (b) Screenshots of the actuated display after n=300, 600, 900 and 1200 in-plane loading cycles. The display shows little attenuation after more than one thousand loading cycles. (c) Experimental setup of the out-of-plane cyclic loading of the device (top-left) and the images from different angles: front view (top-right corner), side view (bottom-left corner) and front-upward view 14


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(bottom-right corner). Iridescent color can be seen in all these figures. (d) Actuated display after out-of-plane cyclic loadings: rows from top to bottom: v=300 mm s-1, 600 mm s-1, 900 mm s-1 and columns from left to right: n=100, 200, 300, where n is the number of the loading cycles. It can be concluded from this figure that the out-of-plane loading has little effect on the display quality. (e) Robustness tests of the device: droping tests (left), tread tests (middle) and stomp tests (right). (f) Actuated display after the treatments in (e). It still remained good functionality under the voltage as high as 2.6kV.

Among all the existing devices for soft display as we discussed above, few work demonstrated the durability of the device which is much essential for the feasibility of generalization. To check the robustness of our device, we performed some fatigue tests, which are shown in Figure 4. Figure 4a-b correspond to the in-plane fatigue tests, c-d the out-of-plane fatigue tests, and e-f the robustness tests. In Figure 4a, we applied a step voltage to the device with an amplitude of 2.6kV and frequency of 1Hz. The CMOS camera was used to record the whole duration of the in-plane loading. Figure 4b shows the states of the device after 300, 600, 900 and 1200 loading cycles, where n in the figure represents the number of loading cycles. It can be clearly seen that the display shows little or no attenuation after more than one thousand cycles. It should be pointed out that the applied voltage of 2.6kV in this test is relatively higher than the regular working voltage to achieve the color display. Hence, the device is supposed to be able to bear more loading cycles in practice. For the out-of-plane loading test, we pushed the center of the display with a glass

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rod in the normal direction of the membrane surface, with the help of the universal testing machine (Instron 5944, USA). Details can be found in our previous work31. The maximum out-of-plane displacement was set as 15mm which is about 300 times of the thickness of the film. The experimental set-up is shown in the top-left corner of Figure 4c. When loading, we recorded the process from different viewing angles, as shown in the top-right corner (front view), bottom-left corner (side view), and bottom-right corner (front-upward view) of Figure 4c. Iridescent color can be seen in all these pictures. When loaded, the deformation field is inhomogeneous, thus the lattice is different especially in the radial direction. What’s more, the incident angle is also different at different point of the film. These two aspects contribute to the colorful appearance of the device. After loading the membrane many cycles at different speed, we smeared the gel electrode on the surfaces and applied a voltage 2.6kV. Figure 4d shows the results for different combinations of loading numbers (n) and loading speed (denoted by v) with three columns for n=100, 200 and 300 (left to right) and the rows for v=300mm s-1, 600 mm s-1 and 900 mm s-1 (top to bottom), respectively. It can be concluded from this figure that hundreds of cycles of out-of-plane loading has little effect on the quality of display since the device can still show the red color from the blue background. As shown in Figure 4e (Supporting Information, Movie), we further abused the device to confirm its outstanding robustness. We firstly dropped the device from about 2m high onto the ground for several times (left in Figure 4e), then we treaded it (middle in Figure 4e) and even stomped (right in Figure 4e) over and over again. 16


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After all these, we connected the resultant device with the power source and it still works fine under the voltage as high as 2.6kV as shown in Figure 4f. All the tests performed above confirm the excellent mechanical reliability and stability of our device. This device can be further transplanted into wearable electronics by replacing the acrylic frame with the soft materials of higher modulus than the VHB film, such as PDMS and silicone. Besides, the device can be made water-proof by encapsulating it with a dielectric layer.

3. Discussion

All the patterns and spectrum characteristics discussed above can be adjusted by changing the initial thickness and pre-stretch of the film, the particle size and the refractive index of the particle. The light source and electrode have great influence on the effect of the display. An ideal light source should be equipped with the ability to control the direction of the emitting light and the desired electrode should be transparent and particularly supple. Besides, the voltage can be dramatically reduced to less than 100V when the thickness of DE is on the order of micrometers32. Another concern for dynamic display is to pixelate the devices with a control system. Absence of either the pixels or control system can make the dynamic display really difficult. For example, Yang et al. came up with a pixelated PC film. However, the resultant pixel color is controlled by the exposure time, not dynamically enough in changing color33. On the other hand, electric control of the pixelated devices is regarded as an ideal way due to its programmability and fast response. With Printing

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Circuit Board technology, this can be easily realized by stacking a layer of row electrodes and a layer of column electrodes at 90° angle on the two sides of the active material layer9, 34-35. These control systems can be directly adopted in our device. Hence, we didn’t concentrate on the control system of the devices. The facile fabrication process, the angle-dependent characteristics, and the excellent mechanical properties incorporating with low-cost and non-toxic features compared with others such as using the QDs or LCs8-9 endow our device great potential in various applications that involve the color display. Besides, compared with other devices using photonic crystals for display, our device also has distinct advantages. For example, Han et al. proposed a display device by photonic crystals20. In this device, the nanoparticles were dispersed in a liquid. When applying an electric voltage on the electrodes, the nanoparticles aggregated to one end, resulting the reduction of the lattice constant. Thus, the color underwent a blue shift with the increasing voltage. Though their device is electric-actuated, the liquid working environment limits its application to some extent. By contrast, our device doesn’t need to work in a liquid environment, which is more desirable. For the static display, we can directly use the patterned electrode without external control system. Instead, for the dynamic display as we mentioned above, we can use the pixelated electrodes and connect the device to a control system, which vastly promotes the development of a new generation of display due to the stretchability and flexibility of the screen. Furthermore, the concept we proposed can be used in identifying and anti-counterfeiting applications since the in-situ color change can provide more 18


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information than the existing anti-counterfeit technologies. In a typical example, we can apply the present concept to the barcode technology as shown in Figure S2 (see Supporting Information). This technology mainly contains two steps: (i) the coding step shown in Figure S2a-b, and (ii) the decoding step shown in Figure S2b-c, d. When coding, the barcode can be compressed by a factor fc resulting in the narrower barcode that can’t be identified by the code scanner shown in Figure S2b. These stripes and gaps can be widened by the controlled voltage that applied across the device. When the voltage reaches a certain value, the stripes recover to its uncoded state thus the scanner can recognize the barcode and read the information. What’s more, the individual color of each stripe can be controlled independently to achieve a further decoding of this barcode (Figure S2d), indicating the vigorous information-carrying capacity of the barcode utilizing the method we put forward. As another representative example, the concept in our study can be used to mimic the camouflage ability of the cephalopods. It is well known that some cephalopods in the sea, like cuttlefish and octopus, are celebrated for their rapid adaptive coloration which is used for camouflage and communication. The skin structure of these cephalopods consists of three main portions: the leucophores (lp) that provide a white background, the chromatophores (cp) which is a type of pigment cell and the iridophores (ip) with multilayer elements36 which reflect the light from the pigment cells. The skin patterning is produced by the neutrally controlled chromatophore organs. This mechanism can inspire the combination of phosphors 19



which act as the pigment cells and the PCs as the iridophores. In details, the phosphors can be sandwiched between two DE films and the PC can be attached on the surface of the DEs. When applied a voltage, the phosphors illuminates and the deformation of DE brings a variation to the lattice constant of PC, leading to the change of surface color of the device. In this procedure, DE acts as the carrier of these two elements. The driving mode is much like the cephalopods as they all use the electric signal to control the color. The examples discussed above demonstrate the great potential of the combination of DEs and PCs. Cooperation of these two metamaterials can yield plentiful novel designs in varieties of applications and deserves more attentions.

4. Conclusions

In summary, we proposed a novel mechanism for soft color display in this paper by combining the PCs and the DEs, which is driven by external voltage. The raw materials are cheap and the fabrication processes are straightforward. A series of fatigue tests including the in-plane and out-of-plane cyclic loadings, and violent treatments, were carried out to demonstrate the reliability and robustness of the final device. The spectrum characteristics and theoretical results reveal that the device can display the color in the whole visible light range, validating the feasibility of full-color display. We believe the present work can pave the way for the next generation soft color display and the concept we used in this paper can inspire varieties of novel applications.

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5.

Experimental Section

5.1. 2D PCs fabrication

The following materials are used to fabricate 2D PCs: polystyrene (PS) particles with diameter of 630 nm purchased from Base Line Co. (2.5 wt % , coefficient of variation less than 10%); ammonium hydroxide, sodium dodecyl sulfate, ethyl alcohol and Polyethylene oxide (PEO, Mw = 100000) obtained from Sigma-Aldrich. All reagents are used as received without any further purification if not specifically stated. Well-ordered closed-packed 2D array of PS beads were directly assembled on the surface of DE using MPI method as previous reported30, 37. In brief, the PS beads (2.5 wt % ) were firstly separated by centrifugation, washed by excessive ethyl alcohol several times and then redispersed in ultrapure water. This PS beads dispersion (10 wt %) was mixed with isopropanol (2:1, v/v) and a trace amount of PEO (2 mg mL−1) to form PS suspension. Next, the ultrapure water was added on the horizontally seated VHB film fixed on the acrylic frame and the PS suspension was slowly and smoothly injected onto the air-water interface by a syringe pump at a rate of 6 µL min-1 to form 2D PS array. The needle’s position is very important to the resultant 2D PS array and it should be just in contact with the water surface. Once the PS suspension reached the surface, the higher surface tension of water pulled the suspension outward and spread the PS particles along the water surface, known as Marangoni effect. When the PS particles covered the whole water surface, we removed most of the water by a medical injector, being careful enough to protect the integrality of the colloid particle layer. In the end, the film was dried in the nitrogen environment and a monolayer of PS 21



particles was ultimately obtained on its surface.

5.2. Device fabrication

The film with 2D PCs was covered with gel electrode on its surfaces. In details, we firstly cut the silicon papers with laser (VLS2.30，Universal Laser System. Inc) to obtain the pre-designed patterns. The patterned silicon papers were then pasted on the two sides of the film to serve masks. After that the commercial available gel electrodes were smeared onto the masks. Finally the copper conductor connects the device with the external power source (Trek model 610E, USA).

5.3. Sample characterization

Scanning electron micrographs were collected using a HITACHI SU8010 high-resolution field emission SEM. A thin layer of gold was sputtered onto each sample before imaging. For the angle-dependent characterization, we use the “5×5” pixelated sample with side length of each pixel 2.94mm and the interval 5.88mm. The scattering spectrums were collected by an angle-resolved spectrum system (R1, ideaoptics, China) equipped with a high sensitive spectrometer (NOVA, ideaoptics, China). The integral time was kept 2000ms for all measurements.

6.

Supporting Information

Circular actuator model; calculation of central wavelength; supporting figures including the configurations of the circular actuator, anti-counterfeit application using the concept in the manuscript; supporting Movie. This material is available free of 22


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charge via the Internet at http://pubs.acs.org.

7.

Author information

Corresponding author: *E-mail: [email protected] Notes: The authors declare no competing financial interest.

8.

Author contributions

T.Y. and S.Q. conceived the idea and designed the research. T.Y., D. Z., and Z.H. prepared the monodisperse PS particles and fabricated the devices. T.Y. and T.W. performed the scattering spectrum experiments and the fatigue tests. J.L., X.L., and H.Y. provided useful suggestions on this work. All authors discussed and analyzed results. T.Y., S.Q., and H.Y. wrote the manuscript with the help of all authors.

9.

Acknowledgements

This work is supported by the National Natural Science Foundation of China (Nos. 11525210, 11621062, 91748209), and the Fundamental Research Funds for the Central Universities. We thank Profs. Lei Shi and Jian Zi from Fudan University as well as Dr. Haiwei Yin from Ideaoptics Inc. for the support on the angle-resolved spectroscopy measurements. We also thank Dr. Junyin Li in Prof. Yong Wang’s group from Zhejiang University for the video processing in the Supporting information.

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10. References

(1) Park, S. I.; Xiong, Y.; Kim, R. H.; Elvikis, P.; Meitl, M.; Kim, D. H.; Wu, J.; Yoon, J.; Yu, C. J.; Liu, Z. Printed Assemblies of Inorganic Light-Emitting Diodes for Deformable and Semitransparent Displays. Science 2009, 325 (5943), 977-981. (2) Kim, H. S.; Brueckner, E.; Song, J.; Li, Y.; Kim, S.; Lu, C.; Sulkin, J.; Choquette, K.; Huang, Y.; Nuzzo, R. G. Unusual Strategies for Using Indium Gallium Nitride Grown on Silicon (111) for Solid-State Lighting. Proceedings of the National Academy of Sciences of the United States of America 2011, 108 (25), 10072-10077. (3) Wang, C.; Hwang, D.; Yu, Z.; Takei, K.; Park, J.; Chen, T.; Ma, B.; Javey, A. User-Interactive Electronic Skin for Instantaneous Pressure Visualization. Nature Materials 2013, 12 (10), 899-904. (4) Kim, H. G.; Kim, K. H.; Kim, J. J. Highly Efficient, Conventional, Fluorescent Organic Light-Emitting Diodes with Extended Lifetime. Advanced Materials 2017, 29 (39), 1702159. (5) Sekitani, T.; Nakajima, H.; Maeda, H.; Fukushima, T.; Aida, T.; Hata, K.; Someya, T. Stretchable Active-Matrix Organic Light-Emitting Diode Display Using Printable Elastic Conductors. Nature Materials 2009, 8 (6), 494-499. (6) White, M. S.; Kaltenbrunner, M.; Głowacki, E. D.; Gutnichenko, K.; Kettlgruber, G.; Graz, I.; Aazou, S.; Ulbricht, C.; Egbe, D. A. M.; Miron, M. C. Ultrathin, Highly Flexible and Stretchable PLEDs. Nature Photonics 2013, 7 (10), 811-816. (7) Liang, J.; Li, L.; Niu, X.; Yu, Z.; Pei, Q. Elastomeric Polymer Light-Emitting Devices and Displays. Nature Photonics 2013, 7 (10), 817-824. (8) Yang, C.; Zhou, S.; Shian, S.; Clarke, D. R.; Suo, Z. Organic Liquid-Crystal Devices Based on Ionic 24


Page 24 of 29

Page 25 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Conductors. Materials Horizons 2017, 4 (6), 1102-1109. (9) Kim, J.; Shim, H. J.; Yang, J.; Choi, M. K.; Kim, D. C.; Kim, J.; Hyeon, T.; Kim, D. H. Ultrathin Quantum Dot Display Integrated with Wearable Electronics. Adv Mater 2017, 29 (38), 1700217. (10) Yang, C. H.; Chen, B.; Zhou, J.; Chen, Y. M.; Suo, Z. Electroluminescence of Giant Stretchability. Advanced Materials 2016, 28 (22), 4480-4484. (11) Smith, N. L.; Hong, Z.; Asher, S. A. Responsive Ionic Liquid-Polymer 2D Photonic Crystal Gas Sensors. Analyst 2014, 139 (24), 6379-6386. (12) Lee, Y. J.; Braun, P. V. Tunable Inverse Opal Hydrogel pH Sensors. Advanced Materials 2003, 15 (7‐8), 563-566. (13) Alexeev, V. L.; Das, S.; Finegold, D. N.; Asher, S. A. Photonic Crystal Glucose-Sensing Material for Noninvasive Monitoring of Glucose in Tear Fluid. Clinical Chemistry 2004, 50 (12), 2353-2360. (14) Ee, H. S.; Agarwal, R. Tunable Metasurface and Flat Optical Zoom Lens on a Stretchable Substrate. Nano Letters 2016, 16 (4), 2818-2823. (15) Yu, C.; Li, Y.; Zhang, X.; Huang, X.; Malyarchuk, V.; Wang, S.; Shi, Y.; Gao, L.; Su, Y.; Zhang, Y. Adaptive Optoelectronic Camouflage Systems with Designs Inspired by Cephalopod Skins. Proceedings of the National Academy of Sciences of the United States of America 2014, 111 (36), 12998-13003. (16) Zhao, Z.; Wang, H.; Shang, L.; Yu, Y.; Fu, F.; Zhao, Y.; Gu, Z. Bioinspired Heterogeneous Structural Color Stripes from Capillaries. Adv Mater 2017, 29 (46), 1704569. (17) Fudouzi, H.; Xia, Y. Photonic Papers and Inks: Color Writing with Colorless Materials. Advanced Materials 2003, 15 (11), 892-896.

25



(18) Ge, J.; Goebl, J.; He, L.; Lu, Z.; Yin, Y. Rewritable Photonic Paper with Hygroscopic Salt Solution as Ink. Advanced Materials 2009, 21 (42), 4259-4264. (19) Wang, M.; Zou, C.; Sun, J.; Zhang, L.; Wang, L.; Xiao, J.; Li, F.; Song, P.; Yang, H. Asymmetric Tunable Photonic Bandgaps in Self‐Organized 3D Nanostructure of Polymer‐Stabilized Blue Phase I Modulated by Voltage Polarity. Advanced Functional Materials 2017, 27 (46), 1702261. (20) Han, M. G.; Shin, C. G.; Jeon, S. J.; Shim, H.; Heo, C. J.; Jin, H.; Kim, J. W.; Lee, S. Full Color Tunable Photonic Crystal from Crystalline Colloidal Arrays with an Engineered Photonic Stop-Band. Advanced Materials 2012, 24 (48), 6438-6444. (21) Ge, J.; Yin, Y. Magnetically Tunable Colloidal Photonic Structures in Alkanol Solutions. Advanced Materials 2008, 20 (18), 3485-3491. (22) Zhang, Y.; Fang, Y.; Li, J.; Zhou, Q.; Xiao, Y.; Zhang, K.; Luo, B.; Zhou, J.; Hu, B. Dual-Mode Electronic Skin with Integrated Tactile Sensing and Visualized Injury Warning. Acs Applied Materials & Interfaces 2017, 9 (42), 37493-37500. (23) Du, X.; Wang, J.; Cui, H.; Zhao, Q.; Chen, H.; He, L.; Wang, Y. Breath-Taking Patterns: Discontinuous Hydrophilic Regions for Photonic Crystal Beads Assembly and Patterns Revisualization. ACS Appl Mater Interfaces 2017, 9 (43), 38117-38124. (24) Tan, P. F.; Wang, C. F.; Wang, X. Q.; Ji, W. Q.; Chen, M.; Chen, S. Highly Crystallized Brilliant Polymeric Photonic Crystals via Repulsion ‐ Induced Precipitation Assembly toward Multiresponsive Colorimetric Films. Macromolecular Materials & Engineering 2016, 301 (11), 1363-1373. (25) Arsenault, A. C.; Puzzo, D. P.; Manners, I.; Ozin, G. A. Photonic-crystal Full-Colour Displays. Nature Photonics 2007, 1 (8), 468-472.

26


Page 26 of 29

Page 27 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(26) Puzzo, D. P.; Arsenault, A. C.; Manners, I.; Ozin, G. A. Electroactive Inverse Opal: A Single Material for All Colors. Angewandte Chemie 2009, 48 (5), 961-965. (27) Brochu, P.; Pei, Q. Advances in Dielectric Elastomers for Actuators and Artificial Muscles. Macromolecular Rapid Communications 2010, 31 (1), 10-36. (28) Ohalloran, A.; Omalley, F.; Mchugh, P. A Review on Dielectric Elastomer Actuators, Technology, Applications, and Challenges. Journal of Applied Physics 2008, 104 (7), 9-19. (29) Mao, G.; Huang, X.; Liu, J.; Li, T.; Qu, S.; Yang, W. Dielectric Elastomer Peristaltic Pump Module with Finite Deformation. Smart Material Structures 2015, 24 (7), 075026-075035. (30) Yin, T.; Zhong, D.; Liu, J.; Liu, X.; Yu, H.; Qu, S. Stretch Tuning of the Debye Ring for 2D Photonic Crystals on a Dielectric Elastomer Membrane. Soft Matter 2018, 14 (7), 1120-1129. (31) Liu, J.; Chen, Z.; Liang, X.; Huang, X.; Mao, G.; Hong, W.; Yu, H.; Qu, S. Puncture Mechanics of Soft Elastomeric Membrane with Large Deformation by Rigid Cylindrical Indenter. Journal of the Mechanics and Physics of Solids 2018, 112, 458-471. (32) Yang, C. H.; Chen, B.; Zhou, J.; Chen, Y. M.; Suo, Z. Electroluminescence of Giant Stretchability. Advanced Materials 2015, 28 (22), 4480-4484. (33) Lee, S-;Yi G-R; Moon J, H; Yang S-M, J. Pine David. Pixellated Photonic Crystal Films by Selective Photopolymerization. Advanced Materials 2010, 18 (16), 2111-2116. (34) Ma, M.; Zhang, Z.; Liao, Q.; Yi, F.; Han, L.; Zhang, G.; Liu, S.; Liao, X.; Zhang, Y. Self-Powered Artificial Electronic Skin for High-Resolution Pressure Sensing. Nano Energy 2017, 32, 389-396. (35) Li, J.; Liang, J.; Li, L.; Ren, F.; Hu, W.; Li, J.; Qi, S.; Pei, Q. Healable Capacitive Touch Screen Sensors Based on Transparent Composite Electrodes Comprising Silver Nanowires and a Furan/Maleimide Diels-Alder Cycloaddition Polymer. Acs Nano 2014, 8 (12), 12874-12882.

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(36) Mäthger, L. M.; Denton, E. J.; Marshall, N. J.; Hanlon, R. T. Mechanisms and Behavioural Functions of Structural Coloration in Cephalopods. Journal of the Royal Society Interface 2009, 6 (Suppl 2), S149-S163. (37) Liu, X.; Wang, J.; Wu, Y.; Fan, T.; Xu, Y.; Tang, L.; Ying, Y. Compact Shielding of Graphene Monolayer Leads to Extraordinary SERS-Active Substrate with Large-Area Uniformity and Long-Term Stability. Scientific Reports 2015, 5, 17167.

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Graphic for table of contents

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Soft Display Using Photonic Crystals on Dielectric Elastomers - ACS

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