In theory, gyroid photonic crystals in butterfly wings exhibit advanced optical properties as a result of their highly interconnected microstructures. Because of the difficulties in synthesizing artificial gyroid materials having periodicity corresponding to visible wavelengths, human-made visible gyroid photonic crystals are still unachievable by self-assembly. In this study, we develop a physical approach-trapping of structural coloration (TOSC)-through which the visible structural coloration of an expanded gyroid lattice in a solvated state can be preserved in the solid state, thereby allowing the fabrication of visible-wavelength gyroid photonic crystals. Through control over the diffusivity and diffusive distance for solvent evaporation, the single-molecular-weight gyroid block copolymer photonic crystal can exhibit desired structural coloration in the solid state without the need to introduce any additives, namely, evapochromism. Also, greatly enhanced reflectivity is observed arising from the formation of porous gyroid nanochannels, similar to those in butterfly wings. As a result, TOSC facilitates the fabrication of the human-made solid gyroid photonic crystal featuring tunable and switchable structural coloration without the synthesis to alter the molecular weight. It appears to be applicable in the fields of optical communication, energy, light-emission, sensors, and displays.

The steric hindrance effect on the hydrogen bonding strength and self-assembly supramolecular structures of the PS-b-PVPh diblock copolymer when blended with P4VP and P2VP homopolymers was investigated.

By choice of large overall molecular weights from 0.5 to 1 M kg/mol, the lamellar microstructures of the high-molecular-weight polystyrene-blockpolyisoprene (PS−PI) block copolymers (BCPs) exhibited various long periods and associated different reflected wavelengths. Interestingly, unique solvatochromism-dependent red-and blue-shift reflective bands could be acquired in the PS−PI BCP gel films using a nonselective neutral solvent as an external stimulus. At low polymer concentration, red-shift of the reflectivity was attributed to the increase of BCP long period by the enhancement of the BCP segregation strength, namely, a thermodynamically controlled swelling process. In contrast, at high polymer concentration (ϕ p > 0.8), the blue-shifting reflectivity resulted from the decrease of the BCP long period by the collapse of polymer chains, namely, a kinetically controlled deswelling process. Also, well-aligned lamellar microstructures were fabricated using a shear-induced microstructural orientation. This provides a simple way to fabricate large-area 1D photonic gel films with uniform reflective colors. ■ INTRODUCTIONPeriodic ordered nanostructures created from bottom up (i.e., self-assembly) approaches are well-known in providing fast and economy processes, functionalized and biocompatible advantages in various application fields. 1 Regarding self-assembly from block copolymers (BCPs), the microphase-separation can be accomplished by the immiscibility from the chemical differences between the constituent blocks. 2 Owing to the various possible ordered microstructures, BCP self-assembly may provide diverse applications for nanotechnological applications and has been intensively investigated. 3−5 Selfassembled BCPs having high molecular weights (M w ) are promising to fabricate organic photonic crystals due to the ordered microphase-separated structures and the appropriate domain spacing with respect to the wavelength of visible light. The optical properties of the photonic crystals are strongly dependent on the lattice structure, domain spacing, dielectric contrast and lattice orientation. 6 By taking advantage of BCP characteristics, manipulation of the photonic properties becomes promising. Accordingly, a variety of the microphaseseparated morphologies from the self-assembly of the high-M w BCPs such as one-dimensional (1-D) lamellae, 2-D hexagonally packed cylinders, and 3-D double gyroid structures are able to give different kinds of photonic crystals with various reflective bandgaps at visible and near-IR frequencies. 7−17 By introducing inorganic materials into the BCP-based photonic crystals through hybridization, the control and enhancement of the photonic properties can be carried out. 18 Also, self-assembled BCP photonic crystals are highly responsive to different kinds of external stimuli such as solvent, temperature and compressive mechanical strain so the shift of wavelength of the bandgap can act as a sensing mechanism. 18−27 In this study, the fabrication of organic BCP photonic gel films from the ...

Large-area and flexible amorphous photonic crystals (APCs) featuring interconnected network microstructures are fabricated using high-molecular-weight polystyrene- block-poly(methyl methacrylate) (PS-PMMA) block copolymers. Kinetically controlled microphase separation combining with synergistic weak incompatibility gives rise to short-range-order network microstructures, exhibiting noniridescent optical properties. Solubility-dependent solvatochromism with distinct responses to various organic solvent vapors is observed in the network-forming APC film. By taking advantage of photodegradation of the PMMA block, nanoporous network-forming films were prepared for subsequent template synthesis of robust SiO- and TiO-based APC films through sol-gel reaction. Consequently, refractive index contrast of the APC film was able to be manipulated, resulting in intensely enhanced reflectivity and increased response rate for detecting solvent vapor. With the integration of self-assembly and photolithography approaches, flexible and robust network-forming APC films with well-defined photopatterned textures are carried out. This can provide a novel means for the design of photopatterned organic or inorganic APC films for sensing solvent vapors.