Jingxia Wang

Bioinspired colloidal photonic crystals with controllable wettability.

Because of the combinatorial advantage of their unique light manipulation properties and potential applications in novel optical devices, colloidal photonic crystals (PCs), the periodic arrangement of monodispersed latex spheres, have attracted interest from researchers. In particular, colloidal PCs exhibit structural colors based on interference effects within their periodic structures. The wavelength of these colors lies in the visible range, making them particularly attractive for a variety of applications. Colloidal PCs are extensively used in templating, catalysis, and chromatographic separations. Inspired by biological PCs with both structural color and specific wettability, researchers have fabricated colloidal PCs with controllable wettability as described in this Account. The wettability can be adjusted by the intrinsic roughness of colloidal crystals in combination with the tunable chemical composition of latex surfaces. Changes in the chemical composition of the latex surface under external stimuli, such as light, electricity, and heat, can reversibly control the wettability of PCs. Furthermore, the hierarchical structure of latex particles can effectively alter the water adhesive force of superhydrophobic colloidal PCs. Patterned PCs with a variety of wettabilities can be assembled using inkjet printing from well-designed latex suspensions. By combining their structural color and specific wettability, we also exemplify some of the promising applications of colloidal PCs as templates for the construction of hierarchical structures, as indicators for controllable transport of liquid droplets, and as color-based sensors for the monitoring changes in their environment. These findings offer innovative insights into the design of novel colloidal PCs and will be of great importance for further applications of these materials.

Colorful humidity sensitive photonic crystal hydrogel

A colorful humidity sensitive photonic crystal (PC) hydrogel was facilely fabricated by infiltrating acrylamide (AAm) solution into a P(St–MMA–AA) PC template and subsequently photo-polymerizing. The color of the samples was sensitive to humidity; it could reversibly vary from transparent to violet, blue, cyan, green and red under various humidity conditions, covering the whole visible range. This could be attributed to the humidity sensitivity of the samples stopband, with a maximum change of 240 nm resulting from the varying humidity. Furthermore, the color response showed good stability under cyclic humidity experiments. As-prepared PAAm–P(St–MMA–AA) PC hydrogel successfully combined the humidity sensitivity of PAAm and structure color of the PC template, which suggested a promising composite material as an economical alternative to traditional humidity sensors, and also provided a new insight into the design and development of novel composite functional materials based on a PC template.

Colloidal photonic crystals with narrow stopbands assembled from low-adhesive superhydrophobic substrates.

This article presents a facile approach to centimeter-scale colloidal photonic crystals (PCs) with narrow stopbands assembled on low-adhesive superhydrophobic substrates. The full-width-at-half-maxima of the stopbands are just 12 nm. The narrow stopbands of colloidal PCs are ascribed to the combined effects of perfectly ordered assembly structure, large-scale crack elimination, decreased void fraction, and sufficient thickness of the colloidal PCs. These properties result from a self-assembly process on a low-adhesive superhydrophobic substrate. Latex suspension on this substrate displays a receding three-phase contact line during evaporation, which releases tensile stress induced by latex shrinkage and results in complete elimination of cracks in the colloidal PCs. Furthermore, the simultaneous assembly of latex particles on the outermost layer of a spread liquid film contributes to the perfectly ordered assembly structure. This facile fabrication of centimeter-scale colloidal PCs with narrow stopbands will offer significant insights into the design and creation of novel optical devices.

Fabrication of large-area patterned photonic crystals by ink-jet printing

Large-area patterned photonic crystals (PCs) with multi-stopbands were facilely fabricated by common ink-jet printers using polymer latex suspensions as inks.

Super-hydrophobic film retards frost formation

Hydrophobic and super-hydrophobic isotactic polypropylene (i-PP) films were prepared and the process of frost formation was investigated. It was found that frost formation is greatly retarded on the super-hydrophobic i-PP surface. During the frost formation, the wettability on the super-hydrophobic film oscillates, while the wettability on the hydrophobic film increases steadily. This special oscillation is due to the micro- and nanometre structures, which leads to the delay of the solidification of liquid water at the three-phase line (TPL) region. This result gives a new explanation for the retardation of frost formation on the super-hydrophobic film surface and will be of great significance for the effective design of anti-frost materials.

Enhancement of photochemical hydrogen evolution over Pt-loaded hierarchical titania photonic crystal

Pt-loaded TiO2 hierarchical photonic crystal photocatalysts are demonstrated to be able to double the hydrogen evolution in the photocatalytic water splitting experiment relative to nanocrystalline TiO2 due to the slow photon enhancement at the stop band edge and multiple scatterings among the photonic crystal segments.

Amplifying fluorescence sensing based on inverse opal photonic crystal toward trace TNT detection

A fluorescence-amplifying method based on photonic crystal (PC) has been demonstrated for trace TNT detection. The fluorescence enhancement for TNT detection on the optimized PC can be up to 60.6-fold in comparison to that of the control sample, which combines the slow photon effect of PC and large surface areas of the inverse opal structure. Furthermore, the quenching efficiency of the PC-based sensor achieves 80% after exposure to TNT vapor for 300 s. The results suggest that the fluorescence-amplifying method based on PC has enormous potential for the development of highly efficient fluorescence sensors toward detection of trace TNT or other explosives.

Hierarchically Macro-/Mesoporous Ti—Si Oxides Photonic Crystal with Highly Efficient Photocatalytic Capability

Hierarchically macro-/mesoporous Ti-Si oxides photonic crystal (i-Ti-Si PC) with highly efficient photocatalytic activity has been synthesized by combining colloidal crystal template and amphiphilic triblock copolymer. It was found that the thermal stability of mesoporous structures in the composite matrix were improved due to the introduction of silica acting as glue and linking anatase nanoparticles together, and the photocatalytic activity of the i-Ti-Si PCs was affected by the calcination conditions. The influences of photonic and structural effect of the i-Ti-Si PCs on photocatalytic activity were investigated. Photodegradation efficiency of the i-Ti-Si PCs was 2.1 times higher than that of TiO(2) photonic crystals (i-TiO(2) PCs) in the photodegradation of Rhodamine B (RB) dye as a result of higher surface area. When the energy of slow photon (SP) was optimized to the abosorption region of TiO(2), a maximum enhanced factor of 15.6 was achieved in comparison to nanocrystalline TiO(2) films (nc-TiO(2)), which originated from the synergetic effect of SP enhancement and high surface area.

Amplification of Fluorescent Contrast by Photonic Crystals in Optical Storage

[*] Prof. Y. Song, Prof. J. Wang, Dr. H. Li, Dr. H. Lin, Dr. L. Xu, Prof. W. Xu, Prof. D. Zhu Beijing National Laboratory for Molecular Sciences (BNLMS) Key Laboratory of Organic Solid, Laboratory of New Materials, Institute of Chemistry The Chinese Academy of Sciences Beijing, 100190 (P. R. China) E-mail: ylsong@iccas.ac.cn Prof. R. Wang, Dr. H. Li Key Laboratory of Micro-nano Measurement, Manipulation and Physics (Ministry of Education) Department of Physics, Beijing University of Aeronautics and Astronautics Beijing, 100191 (P. R. China) E-mail: rmwang@buaa.edu.cn

Solid-state fluorescence enhancement of organic dyes by photonic crystals

Photonic crystal (PC) films were fabricated by self-assembly of colloidal crystals using a vertical deposition method at invariant temperature and humidity. Organic dyes, whose emission wavelengths overlap the photonic stopbands of selected PCs, were deposited on the surface of PC films by thermal evaporation under vacuum. The fluorescence of organic dyes deposited on PCs is obviously enhanced in comparison with that on aluminium films and glass surfaces. There were 41-fold and 20-fold fluorescence enhancements when Rhodamine B base was deposited on the surface of a yellow PC film, compared with that on glass surface and aluminium film respectively, where PCs were utilized as a Bragg reflection mirror. The results show that the PCs are more effective and selective reflection mirrors than aluminium, and have potential applications in optoelectronic and lighting devices.