Iridescent Daytime Radiative Cooling with No Absorption Peaks in the Visible Range

Coatings for passive radiative cooling applications must be highly reflected in the solar spectrum, and thus can hardly support any coloration without losing their functionality. In this work, a colorful daytime radiative cooling surface based on structural coloration is reported. A designed radiative cooler with a bioinspired array of truncated SiO2 microcones is manufactured via a self-assembly method and reactive ion etching. Complemented with a silver reflector, the radiative cooler exhibits broadband iridescent coloration due to the scattering induced by the truncated microcone array while maintaining an average reflectance of 95% in the solar spectrum and a high thermal emissivity (ε) of 0.95, owing to the reduced impedance mismatch provided by the patterned surface at infrared wavelengths, reaching an estimated cooling power of ≈143 W m-2 at an ambient temperature of 25 °C and a measured average temperature drop of 7.1 °C under direct sunlight. This strong cooling performance is attributed to its bioinspired surface pattern, which promotes both the aesthetics and cooling capacity of the daytime radiative cooler

Effect of Carbon Fiber Surface Microstructure on Composite Interfacial Property Based on Image Quantitative Characterization Technique

The surface roughness (Ra) and composite interfacial property of carbon fiber (CF) are considered to be mainly affected by the microstructure of the CF surface. However, quantitative characterization of the CF surface microstructure is always a difficulty. How the CF surface microstructure affects the interfacial property of CF composites is not entirely clear. A quantitative characterization technique based on images was established to calculate the cross-section perimeter and area of five types of CFs, as well as the number (N), width (W) and depth (D) of grooves on these CF surfaces. The CF composite interfacial shear strength (IFSS) was tested by the micro-droplet debonding test and modified by the realistic perimeter. The relationship between the groove structure parameter and the Ra, specific surface area and composite interfacial property was discussed in this article. The results indicated that the CF cross-section perimeter calculated by this technique showed strong consistency with the CF specific surface area and composite interfacial property. At last, the composite interface bonding mechanism based on defect capture was put forward. This mechanism can be a guiding principle for CF surface modification and help researchers better understand and establish interface bonding theories

Preparation of Three-Dimensional Photonic Crystals of Zirconia by Electrodeposition in a Colloidal Crystals Template

Three-dimensional photonic crystals of zirconia were prepared by electrodeposition in a colloidal crystals template following calcination at 500 °C. Scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, and reflectance spectroscopy were employed to characterize the photonic crystals of zirconia. It was found that hydrated zirconium ions could penetrate the colloidal crystals template and reach the substrate easily by electrodeposition, which resulted in stronger bonding between the substrate and the as-deposited membrane. Moreover, the electrodeposited membrane had low water content, leading to a low amount of shrinkage during calcination. Both these properties could suppress detachment from the substrate upon removal of the colloidal crystals template. Therefore, the three-dimensional photonic crystals of zirconia synthesized in this study exhibited very good preservation of the ordered structures of the colloidal crystals template with a high density. A peak of reflection higher than 70% was formed in the reflectance spectrum because of the strong diffraction of the ordered structures

Preparation of Polyimide Films with Ultra-Low Dielectric Constant by Phase Inversion

Due to the high value of its dielectric constant, polyimide does not meet the requirements of the development of integrated circuits and high-frequency printed circuits. The development of novel low dielectric constant polyimide materials for the preparation of flexible copper clad laminates is of theoretical and practical significance in the application of polyimide for 5G communications. In this work, different fluorinated graphene/polyamic acids (FG/PAA) were used as the precursor, and the porous polyimide film was successfully prepared by phase inversion. The dielectric constant of the porous polyimide film is relatively low, being less than 1.7. When the content of fluorinated graphene is 0.5 wt%, the overall dielectric performance of the porous film is the best, with a dielectric constant of 1.56 (10 kHz) and a characteristic breakdown field strength of 56.39 kV/mm. In addition, the mechanical properties of the film are relatively poor, with tensile strengths of 13.87 MPa (0.2 wt%), 13.61 MPa (0.5 wt%), and 6.25 MPa (1.0 wt%), respectively. Therefore, further improving the breakdown resistance and mechanical properties of the porous film is essential for the application of porous ultra-low dielectric polyimide materials

Synthesis of Silica Microspheres—Inspired by the Formation of Ice Crystals—With High Homogeneous Particle Sizes and Their Applications in Photonic Crystals

Silica microspheres (SMs) must possess the performances of desirable monodispersity, narrow particle size distribution, and high sphericity for preparing photonic crystals (PCs) and other materials such as microspheres reference material, etc. We have adopted the techniques of increasing reactant concentration and raising the temperature to improve the synthesis rate of SMs, gaining inspiration from the formation mechanism of ice crystals. SMs with uniform particle sizes (polydispersity index less than 0.05) and good spherical features were fabricated through homogeneous nucleation. The mathematical relationship between particle sizes of SMs and reactant concentrations is further fitted. High accuracy of the regression equation is verified by an F-test and verification experiment. Highly ordered PCs (the stacking fault is about 1.5%, and the point defect is about 10−3) with dense stacked opal structures have been obtained by self-assembly of SMs. In addition, highly ordered PCs (the stacking fault is about 3%, and the point defect is about 10−3) with non-dense packed opal structure and inverse opal structure were successfully prepared. PCs of inverse opal structure were used to examine their response characteristics to identify ethanol, exhibiting good performance. Our research may provide significant inspiration for the development of other sorts of microspheres

MgF2 as abundant and environmentally friendly electrolytes for high performance electrochromic devices

Electrochromic devices (ECDs) can regulate the indoor solar radiation by adjusting optical transmissive properties, showing great commercial potential and important social value of green energy saving. However, the unsafety and high cost of Li+ based electrolyte hinder the large-scale and industrialized production of ECDs. Other metal ions have been used as electrolyte ions, but they are rarely reported in all solid state ECDs. In this study, MgF2 film is used as the solid electrolyte to construct all solid state ECD with the structure of glass/ITO/WO3/MgF2/NiO/ITO. The ECD shows the large optical modulation (∼83% at 820 nm, with 100 s durations) and fast response (19.2 s for bleaching and 8.3 s for coloring, with 25 s durations). Moreover, the ECD achieves the extreme transmittance value of colored states Tc ≈ 0%, which can give an absolute private state. This work not only indicates that MgF2 film can be an alternative to Li+ based electrolyte in all solid state ECDs, but also broadens the applications of all solid state EC smart windows to private buildings