Photonic crystal&electrochromic functional composite materials inspired by nature

Photonic crystals include two kinds of materials with different dielectric constant that were orderly arranged in space. which can control the light propagation and effectively inhibit the spontaneous emission of atoms. The research on PCs has been published twice by Science magazine as "the world's ten major advances in science Photonic crystals existence in many forms in nature such as butterfly wings, skin of beetle shell, opal gemstone. Synthetic microspheres and colloidal crystals were used to simulate the structure of butterfly wings to prepare many kinds of photonic crystals, including the opal structure of silica and polystyrene We have developed method to self-assemble 2D and 3D colloidal crystals. 2D colloidal crystals are monolayer arrays of colloidal microspheres or nanospheres. They are usually assembled on planar substrates or at air/water interface with ordered arrangement. For the preparation of 3D colloidal crystals, the vertical deposition by evaporation technique has been used; the method relies on the balance between sphere sedimentation and evaporation of the colloidal suspension. Evaporation of solvent from the meniscus region draws colloidal spheres into the area of film formation and inter-particle capillary forces assemble the spheres into close packed arrays(Fig. 1). By using spray method, large area PCs could be self-assembled. Colloidal crystals are employed as the templates to structurally direct the formation of inverse opal structures. Based on this template, electrochromic materials of highly ordered and three-dimensional porous structure (3DOM) was prepared such as WO₃,PEDOT, V₂O₅ , Ta₂O₅, CeO₂, Si,Ge . Ge photonic crystal was particularly fist synthesized at room temperature in the world, which conquered the problem of lower filling rate, lower degree of order and higher energy consumption. Two sets of photonic crystal assembly systems had been built, which can provide a variety of substrates with high order, fast and large area assembly, offering technical support for their applications.as showed in Figure.2, and the influence of the introduction of the microstructure on the photo-thermal properties was studied in detail. The results showed that due to the presence of ordered porous structure, the material specific surface area was enhanced, the ion diffusion distance was reduced, the ion diffusion coefficient was improved, so the electrochromic materials photochromic properties were significantly improved, such as enhancing the color contrast, shorten the response time and increased coloration efficiency.In addition, due to the adjustable pore size, the continuous control performance of light and heat can be realized. We used V2O5 to obtain the controllable morphology and structure of one-dimensional electrochromic materials, 3D nanorods can be obtained by pore size of 250nm amorphous three-dimensional ordered macroporous structure of vanadium oxide in heat treatment of 350℃. After heat treatment at 450 ℃, the structure of 3D nanowires can be obtained (Fig. 3). In electrodeposition process, polystyrene microspheres induced heterogeneous nucleation and anisotropy of the orthogonal V2O5 crystal structure were the two important factors causing 3DOM structure change to 3D nanorods packing structure on heat treatment conditions. Due to the higher specific surface area, shorter ion diffusion distance and better electrolyte wetting, these two kinds of one-dimensional structures all showed electrochromic properties of multiple color changes.