Anoplophora graafi longhorn beetle coloration is due to disordered diamond-like packed spheres.

While artificial photonic materials are typically highly ordered, photonic structures in many species of birds and insects do not possess a long-range order. Studying their order-disorder interplay sheds light on the origin of the photonic band gap. Here, we investigated the scale morphology of the Anoplophora graafi longhorn beetle. Combining small-angle X-ray scattering and slice-and-view FIB-SEM tomography with molecular dynamics and optical simulations, we characterised the chitin sphere assemblies within blue and green A. graafi scales. The low volume fraction of spheres and the number of their nearest neighbours are incompatible with any known close-packed sphere morphology. A short-range diamond lattice with long-range disorder best describes the sphere assembly, which will inspire the development of new colloid-based photonic materials.

Robust Full-Spectral Color Tuning of Photonic Colloids.

Creation of color through photonic morphologies manufactured by molecular self-assembly is a promising approach, but the complexity and lack of robustness of the fabrication processes have limited their technical exploitation. Here, it is shown that photonic spheres with full-color tuning across the entire visible spectrum can be readily and reliably achieved by the emulsification of solutions containing a block copolymer (BCP) and two swelling additives. Solvent diffusion out of the emulsion droplets gives rise to 20-150 µm-sized spheres with an onion-like lamellar morphology. Controlling the lamellar thickness by differential swelling with the two additives enables color tuning of the Bragg interference-based reflection band across the entire visible spectrum. By studying five different systems, a set of important principles for manufacturing photonic colloids is established. Two swelling additives are required, one of which must exhibit strong interactions with one of the BCP blocks. The additives should be chosen to enhance the dielectric contrast, and the formation kinetics of the spheres must be sufficiently slow to enable the emergence of the photonic morphology. The proposed approach is versatile and robust and allows the scalable production of photonic pigments with possible future applications in inks for cosmetics and arts, coatings, and displays.

Photonic Particles Made by the Confined Self-Assembly of a Supramolecular Comb-Like Block Copolymer.

Approaches that enable the preparation of robust polymeric photonic particles are of interest for the development of nonfading and highly reflective pigments for applications such as paints and display technologies. Here, the preparation of photonic particles that display structural color in both, aqueous suspension and the dry solid state is reported. This is achieved by exploiting the confined self-assembly of a supramolecular comb-like block copolymer (BCP) that microphase separates into a well-ordered lamellar morphology with dimensions that promote a photonic bandgap in the visible range. The comb-like BCP is formed by robust ionic interactions between poly(styrene-b-4-vinyl-pyridine) (PS-b-P4VP) BCP and dodecylbenzene sulfonic acid (DBSA), which selectively interacts with P4VP blocks. The components are combined in chloroform, and an aqueous emulsion is prepared. Evaporation of the organic solvent leads to the formation of solid microparticles with an onion-like 3D morphology. These photonic pigments display brilliant colors with reflectance spectra featuring pronounced optical bandgaps across the entire visible wavelength range with a peak reflectivity of 80-90%.

Directing Block Copolymer Self-Assembly on Patterned Substrates.

Self-assembling block copolymer films provide access to a variety of different nanostructured patterns in one, two, and three dimensions. However, in the absence of any templating, these nanostructures suffer from defects, often limiting utility. Directed block copolymer self-assembly uses patterned substrates that effectively suppress defect formation and allow the creation of desired patterns. The two main directed self-assembly techniques, chemoepitaxy and graphoepitaxy, employ chemically and topographically patterned substrates, respectively, to direct the block copolymer assembly in thin films. Their successful application in generating defect-free patterns in films of block copolymers exhibiting particular morphologies is summarized in this concept article. The possible role of directed self-assembly in extending nanostructured patterning from two to three dimensions is also discussed.

Controlling Self-Assembly in Gyroid Terpolymer Films By Solvent Vapor Annealing.

The efficacy with which solvent vapor annealing (SVA) can control block copolymer self-assembly has so far been demonstrated primarily for the simplest class of copolymer, the linear diblock copolymer. Adding a third distinct block-thereby creating a triblock terpolymer-not only provides convenient access to complex continuous network morphologies, particularly the gyroid phases, but also opens up a route toward the fabrication of novel nanoscale devices such as optical metamaterials. Such applications, however, require the generation of well-ordered 3D continuous networks, which in turn requires a detailed understanding of the SVA process in terpolymer network morphologies. Here, in situ grazing-incidence small-angle X-ray scattering (GISAXS) is employed to study the self-assembly of a gyroid-forming triblock terpolymer during SVA, revealing the effects of several key SVA parameters on the morphology, lateral order, and, in particular, its preservation in the dried film. The robustness of the terpolymer gyroid morphology is a key requirement for successful SVA, allowing the exploration of annealing parameters which may enable the generation of films with long-range order, e.g., for optical metamaterial applications.

Probing and controlling liquid crystal helical nanofilaments.

We report the first in situ measurement of the helical pitch of the helical nanofilament B4 phase of bent-core liquid crystals using linearly polarized, resonant soft X-ray scattering at the carbon K-edge. A strong, anisotropic scattering peak corresponding to the half-pitch of the twisted smectic layer structure was observed. The equilibrium helical half-pitch of NOBOW is found to be 120 nm, essentially independent of temperature. However, the helical pitch can be tuned by mixing guest organic molecules with the bent-core host, followed by thermal annealing.

An electrolyte additive for the improved high voltage performance of LiNi0.5Mn1.5O4 (LNMO) cathodes in Li-ion batteries.

High-voltage cathode materials are important for the implementation of high-energy-density Li-ion batteries. However, with increasing cut-off voltages, interfacial instabilities between electrodes and the electrolyte limit their commercial development. This study addresses this issue by proposing a new electrolyte additive, (3-aminopropyl)triethoxysilane (APTS). APTS stabilises the interface between the LiNi0.5Mn1.5O4 (LNMO) cathode and the electrolyte in LNMO‖Li half-cells due to its multifunctional character. The amino groups in APTS facilitate the formation of a robust protective cathode layer. Its silane groups improve layer stability by neutralising the electrolyte's detrimental hydrogen fluoride and water. Electrochemical measurements reveal that the addition of 0.5 wt% APTS significantly improves the long-term cycling stability of LNMO‖Li half-cells at room temperature and 55 °C. APTS-addition to the electrolyte delivers excellent capacity retention of 92% after 350 cycles at room temperature and 71% after 300 cycles at 55 °C (1C) contrasting with the much lower performances of the additive-free electrolyte. The addition of a 0.5 wt% (3-glycidyloxypropyl)trimethoxysilane (GLYMO) additive, which contains only the siloxane group, but lacks the amine group, displayed a capacity retention of 73% after 350 cycles at room temperature but degraded significantly upon cycling at 55 °C.

Cellulose nanofiber-reinforced solid polymer electrolytes with high ionic conductivity for lithium batteries.

Lithium-metal electrodes are promising for developing next-generation lithium-based batteries with high energy densities. However, their implementation is severely limited by dendritic growth during battery cycling, which eventually short-circuits the battery. Replacing conventional liquid electrolytes with solid polymer electrolytes (SPEs) can suppress dendritic growth. Unfortunately, in SPEs the high stiffness required for suppressing dendrites comes at the expense of efficient lithium-ion transport. Some polymer-based composite electrolytes, however, enable the decoupling of stiffness and ionic conductivity. This study introduces a composite SPE comprised of a relatively soft poly(ethylene oxide-co-epichlorohydrin) (EO-co-EPI) statistical copolymer with high ionic conductivity and cellulose nanofibers (CNFs), a filler with extraordinary stiffness sourced from abundant cellulose. CNF-reinforcement of EO-co-EPI increases the storage modulus up to three orders of magnitude while essentially maintaining the SPE's high ionic conductivity. The composite SPE exhibits good cycling ability and electrochemical stability, demonstrating its utility in lithium metal batteries.

Directed Self-Assembly of Diamond Networks in Triblock Terpolymer Films on Patterned Substrates.

Block copolymers (BCPs) are particularly effective in creating soft nanostructured templates for transferring complex 3D network structures into inorganic materials that are difficult to fabricate by other methods. However, achieving control of the local ordering within these 3D networks over large areas remains a significant obstacle to advancing material properties. Here, we address this challenge by directing the self-assembly of a 3D alternating diamond morphology by solvent vapor annealing of a triblock terpolymer film on a chemically patterned substrate. The hexagonal substrate patterns were designed to match a (111) plane of the diamond lattice. Commensurability between the sparse substrate pattern and the BCP lattice produced a uniformly ordered diamond network within the polymer film, as confirmed by a combination of atomic force microscopy and cross-sectional imaging using focused ion beam scanning electron microscopy. The successful replication of the complex and well-ordered 3D network structure in gold promises to advance optical metamaterials and has potential applications in nanophotonics.

Mechanically robust supramolecular polymer co-assemblies.

Supramolecular polymers are formed through non-covalent, directional interactions between monomeric building blocks. The assembly of these materials is reversible, which enables functions such as healing, repair, or recycling. However, supramolecular polymers generally fail to match the mechanical properties of conventional commodity plastics. Here we demonstrate how strong, stiff, tough, and healable materials can be accessed through the combination of two metallosupramolecular polymers with complementary mechanical properties that feature the same metal-ligand complex as binding motif. Co-assembly yields materials with micro-phase separated hard and soft domains and the mechanical properties can be tailored by simply varying the ratio of the two constituents. On account of toughening and physical cross-linking effects, this approach affords materials that display higher strength, toughness, or failure strain than either metallosupramolecular polymer alone. The possibility to combine supramolecular building blocks in any ratio further permits access to compositionally graded objects with a spatially modulated mechanical behavior.

Polymer-templated mesoporous lithium titanate microspheres for high-performance lithium batteries.

The spinel Li4Ti5O12 (LTO) is a promising lithium ion battery anode material with the potential to supplement graphite as an industry standard, but its low electrical conductivity and Li-ion diffusivity need to be overcome. Here, mesoporous LTO microspheres with carbon-coatings were formed by phase separation of a homopolymer from microphase-separated block copolymers of varying molar masses containing sol-gel precursors. Upon heating the composite underwent a sol-gel condensation reaction followed by the eventual pyrolysis of the polymer templates. The optimised mesoporous LTO microspheres demonstrated an excellent electrochemical performance with an excellent specific discharge capacity of 164 mA h g-1, 95% of which was retained after 1000 cycles at a C-rate of 10.

Comparing Percolation and Alignment of Cellulose Nanocrystals for the Reinforcement of Polyurethane Nanocomposites.

The reinforcement of polymer nanocomposites can be achieved through alignment or percolation of cellulose nanocrystals (CNCs). Here, we compare the efficacy of these reinforcement mechanisms in thermoplastic polyurethane (PU) elastomer nanocomposites containing thermally stable cotton CNCs. CNC alignment was achieved by melt spinning nanocomposite fibers, while a percolating CNC network was generated by solvent casting nanocomposite films with CNC contents up to 20 wt %. While in films both the CNCs and the PU matrix were entirely isotropic at all concentrations as confirmed by wide-angle X-ray scattering and birefringence analysis, the CNCs in the fibers exhibited a preferential orientation, which improved with increasing CNC concentration. Increasing the CNC concentration in the fibers reduces, however, the alignment of the PU chains, resulting in an entirely isotropic PU matrix at high CNC contents. The mechanical properties of films and fibers were evaluated using stress-strain measurements. Nanocomposite fibers with low CNC content exhibited superior stiffness, extensibility, and strength compared to the films, while the films displayed superior mechanical properties at high CNC concentrations. These findings are rationalized using common semiempirical models describing the reinforcing effects of CNC alignment in fibers (Halpin-Tsai) and CNC percolation in films (percolation model). The formation of a percolating CNC network leads to a stronger reinforcement than CNC alignment, as the reinforcing effect of the latter is limited by the comparably low aspect ratio of CNCs extracted from cotton. As a consequence, above the percolation threshold for cotton CNCs, isotropic nanocomposite PU films show a higher stiffness than aligned nanocomposite PU fibers.

Electrospinning of Cellulose Nanocrystal-Reinforced Polyurethane Fibrous Mats.

We report the electrospinning of mechanically-tunable, cellulose nanocrystal (CNC)-reinforced polyurethanes (PUs). Using high-aspect ratio CNCs from tunicates, the stiffness and strength of electrospun PU/CNC mats are shown to generally increase. Furthermore, by tuning the electrospinning conditions, fibrous PU/CNC mats were created with either aligned or non-aligned fibers, as confirmed by scanning electron microscopy. PU/CNC mats having fibers aligned in the strain direction were stiffer and stronger compared to mats containing non-aligned fibers. Interestingly, fiber alignment was accompanied by an anisotropic orientation of the CNCs, as confirmed by wide-angle X-ray scattering, implying their alignment additionally benefits both stiffness and strength of fibrous PU/CNC nanocomposite mats. These findings suggest that CNC alignment could serve as an additional reinforcement mechanism in the design of stronger fibrous nanocomposite mats.

Tuning the Properties of a UV-Polymerized, Cross-Linked Solid Polymer Electrolyte for Lithium Batteries.

Lithium metal anodes have been pursued for decades as a way to significantly increase the energy density of lithium-ion batteries. However, safety risks caused by flammable liquid electrolytes and short circuits due to lithium dendrite formation during cell cycling have so far prevented the use of lithium metal in commercial batteries. Solid polymer electrolytes (SPEs) offer a potential solution if their mechanical properties and ionic conductivity can be simultaneously engineered. Here, we introduce a family of SPEs that are scalable and easy to prepare with a photopolymerization process, synthesized from amphiphilic acrylic polymer conetworks based on poly(ethylene glycol), 2-hydroxy-ethylacrylate, norbornyl acrylate, and either lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) or a single-ion polymethacrylate as lithium-ion source. Several conetworks were synthesized and cycled, and their ionic conductivity, mechanical properties, and lithium transference number were characterized. A single-ion-conducting polymer electrolyte shows the best compromise between the different properties and extends the calendar life of the cell.

Contrasting Chemistry of Block Copolymer Films Controls the Dynamics of Protein Self-Assembly at the Nanoscale.

Biological systems are able to control the assembly and positioning of proteins with nanoscale precision, as exemplified by the intricate molecular structures within cell membranes, virus capsids, and collagen matrices. Controlling the assembly of biomolecules is critical for the use of biomaterials in artificial systems such as antibacterial coatings, engineered tissue samples, and implanted medical devices. Furthermore, understanding the dynamics of protein assembly on heterogeneous templates will ultimately enable the control of protein crystallization in general. Here, we show a biomimetic, hierarchical bottom-up approach to direct the self-assembly of crystalline S-layers through nonspecific interactions with nanostructured block copolymer (BCP) thin-film templates. A comparison between physically and chemically patterned BCP substrates shows that chemical heterogeneity is required to confine the adhesion and self-assembly of S-layers to specific BCP domains. Furthermore, we show that this mechanism can be extended to direct the formation of collagen fibers along the principal direction of the underlying BCP substrate. The dynamics of protein self-assembly at the solid-liquid interface are followed using in situ high-resolution atomic force microscopy under continuous flow conditions, allowing the determination of the rate constants of the self-assembly. A pattern of alternating, chemically distinct nanoscale domains drastically increases the rate of self-assembly compared to non-patterned chemically homogeneous substrates.

Melt-Spun Nanocomposite Fibers Reinforced with Aligned Tunicate Nanocrystals.

The fabrication of nanocomposite films and fibers based on cellulose nanocrystals (P-tCNCs) and a thermoplastic polyurethane (PU) elastomer is reported. High-aspect-ratio P-tCNCs were isolated from tunicates using phosphoric acid hydrolysis, which is a process that affords nanocrystals displaying high thermal stability. Nanocomposites were produced by solvent casting (films) or melt-mixing in a twin-screw extruder and subsequent melt-spinning (fibers). The processing protocols were found to affect the orientation of both PU hard segments and the P-tCNCs within the PU matrix and therefore the mechanical properties. While the films were isotropic, both the polymer matrix and the P-tCNCs proved to be aligned along the fiber direction in the fibers, as shown using SAXS/WAXS, angle-dependent Raman spectroscopy, and birefringence analysis. Tensile tests reveal that fibers and films, at similar P-tCNC contents, display Young's moduli and strain-at-break that are within the same order of magnitude, but the stress-at-break was found to be ten-times higher for fibers, conferring them a superior toughness over films.

Metasurfaces Atop Metamaterials: Surface Morphology Induces Linear Dichroism in Gyroid Optical Metamaterials.

Optical metamaterials offer the tantalizing possibility of creating extraordinary optical properties through the careful design and arrangement of subwavelength structural units. Gyroid-structured optical metamaterials possess a chiral, cubic, and triply periodic bulk morphology that exhibits a redshifted effective plasma frequency. They also exhibit a strong linear dichroism, the origin of which is not yet understood. Here, the interaction of light with gold gyroid optical metamaterials is studied and a strong correlation between the surface morphology and its linear dichroism is found. The termination of the gyroid surface breaks the cubic symmetry of the bulk lattice and gives rise to the observed wavelength- and polarization-dependent reflection. The results show that light couples into both localized and propagating plasmon modes associated with anisotropic surface protrusions and the gaps between such protrusions. The localized surface modes give rise to the anisotropic optical response, creating the linear dichroism. Simulated reflection spectra are highly sensitive to minute details of these surface terminations, down to the nanometer level, and can be understood with analogy to the optical properties of a 2D anisotropic metasurface atop a 3D isotropic metamaterial. This pronounced sensitivity to the subwavelength surface morphology has significant consequences for both the design and application of optical metamaterials.

Correction to Semicrystalline Block Copolymers in Rigid Confining Nanopores.

[This corrects the article DOI: 10.1021/acs.macromol.7b01567.].

Mesoporous Titania Microspheres with Highly Tunable Pores as an Anode Material for Lithium Ion Batteries.

Mesoporous titania microspheres (MTMs) have been employed in many applications, including (photo)catalysis as well as energy conversion and storage. Their morphology offers a hierarchical structural design motif that lends itself to being incorporated into established large-scale fabrication processes. Despite the fact that device performance hinges on the precise morphological characteristics of these materials, control over the detailed mesopore structure and the tunability of the pore size remains a challenge. Especially the accessibility of a wide range of mesopore sizes by the same synthesis method is desirable, as this would allow for a comparative study of the relationship between structural features and performance. Here, we report a method that combines sol-gel chemistry with polymer micro- and macrophase separation to synthesize porous titania spheres with diameters in the micrometer range. The as-prepared MTMs exhibit well-defined, accessible porosities with mesopore sizes adjustable by the choice of the polymers. When applied as an anode material in lithium ion batteries (LIBs), the MTMs demonstrate excellent performance. The influence of the pore size and an in situ carbon coating on charge transport and storage is examined, providing important insights for the optimization of structured titania anodes in LIBs. Our synthesis strategy presents a facile one-pot approach that can be applied to different structure-directing agents and inorganic materials, thus further extending its scope of application.

Macroscopically ordered hexagonal arrays by directed self-assembly of block copolymers with minimal topographic patterns.

A simple and robust method has been developed for the generation of macroscopically ordered hexagonal arrays from the directed self-assembly (DSA) of cylinder-forming block copolymers (BCPs) based on minimal trench patterns with solvent vapor annealing. The use of minimal trench patterns allows us to probe the guided hexagonal arrays of cylindrical microdomains using grazing incidence small angle X-ray scattering (GISAXS), where the sample stage is rotated on the basis of the six-fold symmetry of a hexagonal system. It is found that the (10) planes of hexagonal arrays of cylindrical microdomains are oriented parallel to the underlying trench direction over macroscopic length scales (∼1 × 1 cm2). However, there are misorientations of the hexagonal arrays with short-range ordering. GISAXS patterns show that the hexagonal arrays on the minimal trench pattern are distorted, deviating from a perfect hexagonal lattice. This distortion has been attributed to the absence of topographic constraints in the unconfined direction on the 1-D minimal trench pattern. Also, the frustration of BCP microdomains, arising from the incommensurability between the trench pitch and natural period of the BCP at the base of the trench, influences the distortion of the hexagonal arrays.