Oxidation-degree-dependent moisture-induced actuation of a graphene oxide film.

Multilayered films prepared from graphene oxide (GO) subjected to a single oxidation process (1GO) can actuate in response to moisture, whereas those prepared from GO subjected to two oxidation processes (2GO) lose this ability. To elucidate the origin of this difference, the structures and properties of various multilayered films and their contents were analyzed. According to atomic force microscopy images, the lateral size of the GO monolayer in 2GO (2.0 ± 0.4 µm) was smaller than that in 1GO (3.2 ± 0.4 µm), although this size difference did not affect actuation. Scanning electron microscopy images of the cross sections of both films showed fine multilayered structures and X-ray diffraction measurements showed the moisture sensitive reversible change in the interlayer distances for both films. Both films adsorbed 30 wt% moisture in 60 s with different water contents at the bottom moist sides and top air sides of the films. Nanoindentation experiments showed hardness values (1GO: 156 ± 67 MPa; 2GO: 189 ± 97 MPa) and elastic modulus values (1GO: 4.7 ± 1.7 GPa; 2GO: 5.8 ± 3.2 GPa) typical of GO, with no substantial difference between the films. On the contrary, the 1GO film bent when subjected to a weight equal to its own weight, whereas the 2GO film did not. Such differences in the macroscopic hardness of GO films can affect their moisture-induced actuation ability.

Two-Step Divergent Synthesis of Monodisperse and Ultra-Long Bottlebrush Polymers from an Easily Purifiable ROMP Monomer.

The longest bottlebrush polymers reported so far (up to 7 µm in length) were synthesized in two steps from a norbornene derivative bearing two 2-bromoisobutylate moieties (NB). The key to this achievement is the excellent reactivity of NB in ring opening metathesis polymerization, which proceeded in a well-controlled manner with quantitative conversion of NB for monomer-initiator ratios ranging up to 10,000. The resultant polymer derived from NB was readily converted to various bottlebrush polymers in a divergent synthetic route by grafting vinyl monomers from the 2-bromoisobutylate units in NB via atom transfer radical polymerization. The structure of the ultra-long bottlebrush polymer was directly observed using atomic force microscopy.

Bottlebrush polymer-reinforced transparent multiphase plastics with enhanced thermal stability.

Bottlebrush polymers (BPs) are highly tunable with regard to their glass transition temperature, refractive index, and shape. Herein, well-defined BPs were implemented as soft fillers to toughen multiphase plastics without loss of transparency and thermal stability, providing superior fracture toughness than a conventional linear polymer (LP). This study discloses a novel application of BPs and paves the way toward their further development.

Author Correction: Layered nanocomposites by shear-flow-induced alignment of nanosheets.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Layered nanocomposites by shear-flow-induced alignment of nanosheets.

Biological materials, such as bones, teeth and mollusc shells, are well known for their excellent strength, modulus and toughness1-3. Such properties are attributed to the elaborate layered microstructure of inorganic reinforcing nanofillers, especially two-dimensional nanosheets or nanoplatelets, within a ductile organic matrix4-6. Inspired by these biological structures, several assembly strategies-including layer-by-layer4,7,8, casting9,10, vacuum filtration11-13 and use of magnetic fields14,15-have been used to develop layered nanocomposites. However, how to produce ultrastrong layered nanocomposites in a universal, viable and scalable manner remains an open issue. Here we present a strategy to produce nanocomposites with highly ordered layered structures using shear-flow-induced alignment of two-dimensional nanosheets at an immiscible hydrogel/oil interface. For example, nanocomposites based on nanosheets of graphene oxide and clay exhibit a tensile strength of up to 1,215 ± 80 megapascals and a Young's modulus of 198.8 ± 6.5 gigapascals, which are 9.0 and 2.8 times higher, respectively, than those of natural nacre (mother of pearl). When nanosheets of clay are used, the toughness of the resulting nanocomposite can reach 36.7 ± 3.0 megajoules per cubic metre, which is 20.4 times higher than that of natural nacre; meanwhile, the tensile strength is 1,195 ± 60 megapascals. Quantitative analysis indicates that the well aligned nanosheets form a critical interphase, and this results in the observed mechanical properties. We consider that our strategy, which could be readily extended to align a variety of two-dimensional nanofillers, could be applied to a wide range of structural composites and lead to the development of high-performance composites.

Durable and Flexible Superhydrophobic Materials: Abrasion/Scratching/Slicing/Droplet Impacting/Bending/Twisting-Tolerant Composite with Porcupinefish-Like Structure.

Superhydrophobic materials with micro/nanotextured surface have attracted tremendous attention owing to their potential applications such as self-cleaning, antifouling, anti-icing, and corrosion prevention. Such a micro/nanotextured surface is a key for high water repellency. However, such a texture is fragile and readily damaged when the material is deformed, scratched, or sliced off. Thus, it is challenging to develop superhydrophobic materials that can sustain high water repellency after experiencing such a mechanical deformation and damage. Here we report abrasion/scratching/slicing/droplet impacting/bending/twisting-tolerant superhydrophobic flexible materials with porcupinefish-like structure by using a composite of micrometer-scale tetrapod-shaped ZnO and poly(dimethylsiloxane). Owing to the geometry of the tetrapod and elasticity of poly(dimethylsiloxane), the composite material exhibits stable water repellency after 1000 abrasion and 1000 bending cycles, or even after their surfaces were sliced off many times. The material maintains superhydrophobicity even under a mechanically deformed state such as bending and twisting. The materials can be painted on a variety of substrates and molded into desired shapes and used in a myriad of applications that require superhydrophobicity.

An Anisotropic Hydrogel Actuator Enabling Earthworm-Like Directed Peristaltic Crawling.

Peristaltic crawling, which is the moving mechanism of earthworm-like limbless creatures in narrow spaces, is a challenging target to mimic by using soft materials. Here we report an unprecedented hydrogel actuator that enables not only a peristaltic crawling motion but also reversing its direction. Our cylindrically processed hydrogel contains gold nanoparticles for photothermal conversion, a thermoresponsive polymer network for switching the electrical permittivity of the gel interior, and cofacially oriented 2D electrolytes (titanate nanosheets; TiNSs) to synchronously change their anisotropic electrostatic repulsion. When a hydrogel, which was designed to include cofacially oriented TiNSs along the cylindrical gel axis, is pointwisely photoirradiated with a visible-light laser, it spatiotemporally expands immediately (<0.5 s) and largely (80 % of its original length) in an isovolumetric manner. When the irradiation spot is moved along the cylindrical gel axis, the hydrogel undergoes peristaltic crawling due to quick and sequential elongation/contraction events and moves oppositely toward the laser scanning direction. Thus, when the scanning direction is switched, the crawling direction is reversed. When gold nanorods are used in place of gold nanoparticles, the hydrogel becomes responsive to a near-infrared light, which can deeply penetrate into bio tissues.

Preparation of mesoporous silica thin films by photocalcination method and their adsorption abilities for various proteins.

Mesoporous silica (MPS) thin film biosensor platforms were established. MPS thin films were prepared from tetraethoxysilane (TEOS) via using sol-gel and spin-coating methods using a poly-(ethylene oxide)-block-poly-(propylene oxide)-block-poly-(ethylene oxide) triblock polymer, such as P123 ((EO)20(PO)70(EO)20) or F127 ((EO)106(PO)70(EO)106), as the structure-directing agent. The MPS thin film prepared using P123 as the mesoporous template and treated via vacuum ultraviolet (VUV) irradiation to remove the triblock copolymer had a more uniform pore array than that of the corresponding film prepared via thermal treatment. Protein adsorption and enzyme-linked immunosorbent assay (ELISA) on the synthesized MPS thin films were also investigated. VUV-irradiated MPS thin films adsorbed a smaller quantity of protein A than the thermally treated films; however, the human immunoglobulin G (IgG) binding efficiency was higher on the former. In addition, protein A-IgG specific binding on MPS thin films was achieved without using a blocking reagent; i.e., nonspecific adsorption was inhibited by the uniform pore arrays of the films. Furthermore, VUV-irradiated MPS thin films exhibited high sensitivity for ELISA testing, and cytochrome c adsorbed on the MPS thin films exhibited high catalytic activity and recyclability. These results suggest that MPS thin films are attractive platforms for the development of novel biosensors.

[m × n] metal ion arrays templated by coordination cages.

Three-dimensional m × n arrays of metal ion clusters can be assembled as aromatic stacks of planar polynuclear metal complexes within columnar coordination cages. The polynuclear complexes and cage height program the final array structures of the metal ion clusters. Cyclic trinuclear Au(I) complexes (m = 3) assembled into trigonal prismatic arrays (n = 1-3) within the cages and the array structures were clearly shown by X-ray crystallographic analysis. A silver-sandwiched hetero-Au(3)-Ag-Au(3) cluster was also prepared by treating a hexanuclear Au(3)-Au(3) cluster with Ag(I) ion.

Self-assembled cage as an endo-template for cyclophane synthesis.

An organic-pillared coordination cage templated the quantitative formation of siloxane-bridged cyclophanes within its cavity via hydrolysis and condensation of 1,6- and 1,8-bis(trimethoxysilyl)pyrene.

m x n stacks of discrete aromatic stacks in solution.

Septuple columnar stacks of large aromatic molecules with solubilizing side chains have been synthesized via one-step multicomponent self-assembly. At increased concentrations in aqueous solution, m x n aggregates of aromatic stacks form. The simple addition of water induces lyotropic liquid-crystalline mesophases.

Selective synthesis of allenes and alkynes through ligand-controlled, palladium-catalyzed decarboxylative hydrogenolysis of propargylic formates.

Ligand-controlled regioselective palladium-catalyzed decarboxylative hydrogenolysis of propargylic formates is described. A wide range of allenes and alkynes were obtained by using either 1,2-diphenylphosphinoethane (DPPE) or 1,6-bisdiphenylphosphinohexane (DPPH) as a catalyst ligand.

Engineering double to quintuple stacks of a polarized aromatic in confined cavities.

Discrete, well-defined stacks of the polarized aromatic pyrene-4,5-dione (1) were assembled in the cavities of organic-pillared coordination cages (2). The number (n) of stacked guests depends on the pillar length, and up to quintuple stacks (n = 5) were observed when long (16.5 A) organic pillar ligands were incorporated. As previously reported, pyrene-4,5-dione (1) assembles into infinite columnar stacks in the solid state, but the present work demonstrates that the polarized 1 has a strong propensity to stack in layers even in the absence of crystal packing effects. For n = 2 and 3 structures, crystallographic studies revealed that 1 stacks by pi-pi interactions in the cavity in such a way that a net dipole moment is canceled. These results emphasize the important role of dipole-dipole interactions as well as pi-stacking interactions in the formation of columnar stacks of 1.

Engineering discrete stacks of aromatic molecules.

Intrigued by transannular interactions occurring in stacked aromatic molecules, chemists have long endeavored to engineer discrete stacks of specific lengths and orientation. The maturation of self-assembly methodologies has shifted the focus away from utilizing covalent scaffolds to harnessing non-covalent interactions such as ionic interactions, hydrogen bonds, metal-ligand interactions, and aromatic interactions. Aromatic molecules often assemble into ill-defined, infinite aggregates and thus multiple self-assembly techniques must be combined to achieve the desired stack size and conformations. This critical review briefly highlights covalent scaffolds of stack aromatics before focusing on modern self-assembly based strategies for engineering discrete stacks of aromatic molecules (149 references).

Molecular recognition and self-assembly special feature: discrete stack of an odd number of polarized aromatic compounds revealing the importance of net vs. local dipoles.

Three polarized aromatic guest molecules (pyrene-4,5-dione, 1) form a triple-layered stack in the box-shaped cavity of an organic pillared coordination cage in water. The cavity size strictly limits the number of stacked planar guests but does not restrict guest orientation, and thus enables the study of discrete stacks of polarized guests and their preferred conformations. Crystallographic study shows that the guest molecules in the cavity are rotated 120 degrees with respect to each other, cancelling the net dipole moment rather than the local dipole moment. The unique conformation of a discrete, triple stack of 1 sharply contrasts to the standard head-to-tail conformation in infinite stacks of 1.

Engineering stacks of aromatic rings by the interpenetration of self-assembled coordination cages.

One-step quantitative self-assembly of aromatic towers consisting of seven to nine discretely stacked aromatic rings is achieved from 25-27 multicomponents via the interpenetration of two identical coordination cages.

Ruthenium-catalyzed reactions of 1-cyclopropyl-2-propyn-1-ols with anilines and water via allenylidene intermediates: selective preparation of tri- and tetrasubstituted conjugated enynes.

Ruthenium-catalyzed efficient preparation of the conjugated enynes can be carried out in the reactions of 1-cyclopropyl-2-propyn-1-ols with nitrogen- and oxygen-centered nucleophiles such as anilines and water in the presence of a catalytic amount of sulfur-bridged diruthenium complexes. The use of such complexes as catalysts realizes the completely stereoselective preparation of tri- and tetrasubstituted conjugated enynes, where ruthenium-allenylidene complexes work as key intermediates. The direct attack of nucleophiles on a cyclopropane ring connected to an allenylidene ligand is a key step to obtain the enynes stereoselectively.