The first steric-repulsion-based magnetically responsive photonic crystals (MRPCs) is constructed by synthesizing uniform superparamagnetic polyvinylpyrrolidone-coated Fe3 O4 colloidal nanocrystal clusters. The color tunable range of the MRPCs can not only cover almost the entire visible specztrum in solvents of diverse polarities, but also is insusceptible to ionic strength or pH values, facilitating the practical applications of MRPCs.

Microenvironment sensing and imaging are of importance in microscale zones like microreactors, microfluidic systems, and biological cells. But they are so far implemented only based on chemical colors from dyes or quantum dots, which suffered either from photobleaching, quenching, or photoblinking behaviors, or from limited color gamut. In contrast, structural colors from hydrogel-based photonic crystals (PCs) may be stable and tunable in the whole visible spectrum by diffraction peak shift, facilitating the visual detection with high accuracy. However, the current hydrogel-based PCs are all inappropriate for microscale detection due to the bulk size. Here we demonstrate the smallest hydrogel-based PCs, responsive hydrogel-based photonic nanochains with high-resolution and real-time response, by developing a general hydrogen bond-guided template polymerization method. A variety of mechanically separated stimuli-responsive hydrogel-based photonic nanochains have been obtained in a large scale including those responding to pH, solvent, and temperature. Each of them has a submicrometer diameter and is composed of individual one-dimensional periodic structure of magnetic particles locked by a tens-of-nanometer-thick peapod-like responsive hydrogel shell. Taking the pH-responsive hydrogel-based photonic nanochains, for example, pH-induced hydrogel volume change notably alters the nanochain length, resulting in a significant variation of the structural color. The submicrometer size endows the nanochains with improved resolution and response time by 2-3 orders of magnitude than the previous counterparts. Our results for the first time validate the feasibility of using structural colors for microenvironment sensing and imaging and may further promote the applications of responsive PCs, such as in displays and printing.

No abstract

Instant radical polymerization of sterically stabilized magnetically responsive photonic crystal nonaqueous suspensions under magnetic field can obtain flexible thermochromic free-standing films, which display bright iridescent colors strongly sensitive to temperature with good reversibility and durability.

No abstract

The responsive photonic crystal (RPC) balls with adjustable lattice constant and controllable rotation developed to date are all based on Janus particles of three dimensional (3-D) periodical structures, which suffer from color uneveness and asymmetric volume change, limiting the applications in the fields of encoding, sensing and displays. In this study, we have developed the first 1-D magnetic photonic crystal balls with tunable lattice constants by fixing collectively oriented periodical 1-D magnetic nanochain-like structures in responsive polymer poly(N-isopropylacrylamide) hydrogel balls under magnetic field (H) and UV irradiation. The structural colors of the balls are uniform on the entire ball and can be regulated by temperature (T) and solvents. The as-prepared RPC balls always retain a perfectly spherical shape even when the hydrogel volume changes with stimuli because of the low content of the included 1-D magnetic nanochain-like structures. This endows smooth rotation in the H direction to switch "on/off" their structural colors at various stimuli, as demonstrated by a colorful display application at temperature ranging from 10 to 35 °C. The as-developed RPC balls are expected to have promising potential applications in color display, rewritable signage, biological and chemical sensors owing to their excellent multi-response properties.

Polymeric photocatalysts for water splitting have received extensive attention recently. However, most polymeric photocatalysts suffer from an unexceptional hydrogen/oxygen evolution rate, primarily originating from less understanding of the molecular design of conjugated polymers for photocatalysis. Herein, we show that facile substituent regulation on conjugated polymers can boost the hydrogen evolution efficiency. Conjugated polyelectrolytes with different substituent groups (−F, −CN) were designed and synthesized. Compared to the unmodified polymer, the −F and −CN modified polymers showed 2.9-and 12-times improvements in the hydrogen evolution rate (3 μmol h −1 vs 8.8 μmol h −1 vs 38.3 μmol h −1 ). Notably, −CN substituents in the polymer could reduce the exciton binding energy, induce closer packing and higher crystallinity, improve the charge transporting, and reduce the charge recombination. Moreover, higher efficient exciton generation and charge transfer efficiency to cocatalysts were observed in −CN modified polymers, indicating the great promise of using substituent regulation to achieve high-performance organic photocatalysts.

The development of multifunctional artificial cilia may inspire a new generation of intelligent biomimetic microdevices and microfluidic systems, but remains a great challenge. Here, self-adaptive magnetic photonic nanochain cilia arrays (SMPNCAs) capable of achieving real-time and in situ visual microenvironment detection and self-adaptive fluid pumping are shown. By combining magnetic assembly and UV-assisted hydrogen bond-guided template polymerization in printing, SMPNCAs consisting of individual 1D periodic structure of magnetic nanoparticles encapsulated in pH-responsive hydrogel shells, as an example, are demonstrated to be printed on a glass substrate with defined patterns in one step. The as-printed SMPNCAs exhibit real-time adjustable interparticle distance (lattice constant) and total length in response to the reversible volume change of the hydrogel shell with the pH value of the pumped fluids. Consequently, they can sense the surrounding pH variation in real time by in situ displaying different diffracted color, and pump directional flows with self-adaptive flow velocity under a rotating magnetic field. Benefiting from the integration of the facile, robust printing fabrication, structure-color-based fast sensing, and self-adaptive fluid pumping, the SMPNCAs that are developed here promise a significant advancement in biomimicry and microfluidic systems.