Trapping Structural Coloration by a Bioinspired Gyroid Microstructure in Solid State

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

Trapping Structural Coloration by a Bioinspired Gyroid Microstructure in Solid State

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

Trapping Structural Coloration by a Bioinspired Gyroid Microstructure in Solid State

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

Trilayered Single Crystals with Epitaxial Growth in Poly(ethylene oxide)-<i>block</i>-poly(ε-caprolactone)-<i>block</i>-poly(l‑lactide) Thin Films

Manipulation of crystalline textures of biocompatible block copolymers is critical for the applications in the medical field. Here, we present the control of multiple-crystalline morphologies with flat-on chain orientation in biocompatible poly­(ethylene oxide)-<i>block</i>-poly­(ε-caprolactone)-<i>block</i>-poly­(l-lactide) (PEO–PCL–PLLA) triblock copolymer thin films using melt and solvent-induced crystallizations. Only single-crystalline morphologies of the first-crystallized blocks can be obtained in the melt-crystallized thin films due to the confinement effect. With solvent annealing by PCL-selective toluene, single-crystalline PLLA to double-crystalline PLLA/PCL and to triple-crystalline PLLA/PCL/PEO layered crystals in sequence are observed for the first time. With the control of solvent selectivity, different sequential crystallization involving first-crystallized PCL transferring to double-crystalline PCL/PLLA is obtained using PEO-selective <i>n</i>-hexanol for annealing. Surprisingly, the crystalline growth of the trilayered single crystal exhibits specific layer-by-layer epitaxial relationship. As a result, the multiple-crystalline textures of the PEO–PCL–PLLA thin films can be carried out by controlling solvent and polymer interaction

Flexible or Robust Amorphous Photonic Crystals from Network-Forming Block Copolymers for Sensing Solvent Vapors

Large-area and flexible amorphous photonic crystals (APCs) featuring interconnected network microstructures are fabricated using high-molecular-weight polystyrene-<i>block</i>-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 SiO₂- and TiO₂-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

Flexible or Robust Amorphous Photonic Crystals from Network-Forming Block Copolymers for Sensing Solvent Vapors

Large-area and flexible amorphous photonic crystals (APCs) featuring interconnected network microstructures are fabricated using high-molecular-weight polystyrene-<i>block</i>-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 SiO₂- and TiO₂-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

Nanoporous Crystalline Templates from Double-Crystalline Block Copolymers by Control of Interactive Confinement

Single, double, and coincident crystallizations under hard or soft confinement are all carried out using a single type of syndiotactic poly­(<i>p</i>-methyl­styrene)-<i>block</i>-poly­(l-lactide) (<i>s</i>PPMS–PLLA) block copolymers. The single crystallization of <i>s</i>PPMS matrix can lead to the disordered arrangement of hexagonally packed PLLA cylinders under soft confinement. In contrast, the lamellar nanostructure remained unchanged regardless of the PLLA crystallization under hard or soft confinement. Crystallization-induced morphological transitions from the confined monosized lamella to the metastable dual-sized lamella and finally to the breakout morphology are evident by transmission electron microscopy and small-angle X-ray scattering. The dual-sized lamella is attributed to the thermodynamically and kinetically controlled nanocrystallite growth templating along the ordered microphase separation. Despite crystalline sequences, the double-crystallized morphologies are determined by the first-crystallized event even though the subsequent crystallization temperature is performed under soft confinement. By the control of interactive confinement, ordered crystalline nanosheets and cylindrical monoliths are obtained, providing a novel means for the fabrication of nanoporous crystalline templates

Helical Phase Driven by Solvent Evaporation in Self-Assembly of Poly(4-vinylpyridine)-<i>block</i>-poly(l‑lactide) Chiral Block Copolymers

A series of chiral block copolymers (BCPs*), poly­(4-vinylpyridine)-<i>block</i>-poly­(l-lactide) (P4VP–PLLA), are synthesized through atom transfer radical polymerization and living ring-opening polymerization. Except for typical microphase-separated phases, such as lamellae (L) and hexagonally packed cylinders (HC), a helical phase (H*) with hexagonally packed PLLA helices in a P4VP matrix can be found in the self-assembly of P4VP–PLLA BCPs*, reflecting the chirality effect on BCP self-assembly. The H* formation is strongly dependent upon the solvent evaporation rate for solution casting at which fast evaporation gives the H* phase and slow evaporation results in the HC phase. To further examine the metastability of the H* phase associated with the dynamics of BCP* chains during self-assembly, P4VP–PLLA BCPs* having different molecular weights at a constant composition are utilized for self-assembly. Under the same evaporation rate for solution casting, the H* phase can be obtained in high-molecular-weight P4VP–PLLA BCP* whereas a stable HC phase is found in low-molecular-weight P4VP–PLLA BCP*, indicating the kinetic origin of H* formation due to the long and highly entangled chains in solution for self-assembly. Consequently, the H* phase can be driven by solvent evaporation through a kinetically trapped process and is regarded as a long-lived metastable phase

Live Templates of a Supramolecular Block Copolymer for the Synthesis of Ordered Nanostructured TiO₂ Films via Guest Exchange

In this work, we introduce a facile method based on host–guest chemistry to synthesize a range of nanostructured TiO₂ materials using supramolecular templates of a dendron-jacketed block copolymer (DJBCP). The DJBCP is composed of amphiphilic dendrons (4′-(3,4,5-trido­decyl­oxy­benzoyl­oxy)­benzoic acid, TDB) selectively incorporated into a P4VP block of polystyrene-<i>block</i>-poly­(4-vinyl­pyridine) (PS-<i>b</i>-P4VP) via hydrogen bonding. The PS-<i>b</i>-P4VP host acts as a structure-directing template, while the guest molecules (TDB) assist the self-assembly nanostructures and zone-axis alignment, resulting in the nanostructured template of vertically oriented cylinders formed via successive phase transformations from <i>Im</i>3̅<i>m</i> to <i>R</i>3̅<i>m</i> to <i>P</i>6<i>mm</i> upon thermal annealing in the doctor-blade-cast film. The guest molecules subsequently direct the titania precursors into the P4VP domains of the templates via supramolecular guest exchange during immersion of the film in a designated precursor solution containing a P4VP-selective solvent. The subsequent UV irradiation step leads to the formation of PS-<i>b</i>-P4VP/​TiO₂ hybrids. Finally, removal of the host template by calcination leaves behind mesoporous channels and makes sacrifices to be a carbon source for carbon-doping TiO₂ materials. Various TiO₂ nanoarchitectures, namely, vertical and wiggly micrometer-length channels, inverse opals, fingerprint-like channels, heterogeneous multilayers, and nanotubes, have been fabricated by highly tunable DJBCP nanostructures

Self-Assembled Hierarchical Superstructures from the Benzene-1,3,5-Tricarboxamide Supramolecules for the Fabrication of Remote-Controllable Actuating and Rewritable Films

The well-defined hierarchical superstructures constructed by the self-assembly of programmed supramolecules can be organized for the fabrication of remote-controllable actuating and rewritable films. To realize this concept, we newly designed and synthesized a benzene-1,3,5-tricarboxamide (BTA) derivative (abbreviated as BTA-3AZO) containing photoresponsive azobenzene (AZO) mesogens on the periphery of the BTA core. BTA-3AZO was first self-assembled to nanocolumns mainly driven by the intermolecular hydrogen-bonds between BTA cores, and these self-assembled nanocolumns were further self-organized laterally to form the low-ordered hexagonal columnar liquid crystal (LC) phase below the isotropization temperature. Upon cooling, a lamello-columnar crystal phase emerged at room temperature via a highly ordered lamello-columnar LC phase. The three-dimensional (3D) organogel networks consisted of fibrous and lamellar superstructures were fabricated in the BTA-3AZO cyclohexane-methanol solutions. By tuning the wavelength of light, the shape and color of the 3D networked thin films were remote-controlled by the conformational changes of azobenzene moieties in the BTA-3AZO. The demonstrations of remote-controllable 3D actuating and rewritable films with the self-assembled hierarchical BTA-3AZO thin films can be stepping stones for the advanced flexible optoelectronic devices