Tin Oxide Meshes Consisting of Nanoribbons Prepared through an Intermediate Phase in an Aqueous Solution

Novel nanoarchitectures of SnO and SnO2 crystals that had two- and three-dimensionally meshed structures consisting of nanoribbons were prepared through Sn6O4(OH)4 as an intermediate state. Two-dimensional meshes consisting of oriented nanoribbons of single-crystalline tin monoxide (SnO) that was 50−300 nm wide were grown via Sn6O4(OH)4, which was initially produced at room temperature. Textured spherical particles with three-dimensional meshed nanostructures were produced at 60 °C in the presence of citric acid in the aqueous system. The formation of the specific architectures is ascribed to the densely branching growth of SnO crystals in a matrix of Sn6O4(OH)4 as a reactant. The meshed nanostructures of rutile-type tin dioxide were successfully obtained by oxidation of the SnO crystals without deformation of their architectures

Morphological Evolution of Inorganic Crystal into Zigzag and Helical Architectures with an Exquisite Association of Polymer: A Novel Approach for Morphological Complexity

The morphology of potassium sulfate (K2SO4) crystals grown in a viscous polymer solution of poly(acrylic acid) (PAA) was remarkably changed from the tilted columnar assembly into zigzag and helical architectures with increasing PAA concentration. The habit modification of orthorhombic K2SO4 with adsorption of PAA molecules on a specified crystal face fundamentally led to the formation of tilted unit crystals. Concurrently with the habit modification, a diffusion-limited condition controlling the assembly of tilted units was achieved in the presence of PAA molecules in the matrix. Various complex morphologies, including zigzag and helical assembly, emerged through the formation of twinned crystals with the variation of the diffusion condition. Understanding the morphogenesis observed in this report would provide a novel approach for sophisticated crystal design by using an exquisite association of organic and inorganic materials

Morphological Evolution of Inorganic Crystal into Zigzag and Helical Architectures with an Exquisite Association of Polymer: A Novel Approach for Morphological Complexity

The morphology of potassium sulfate (K2SO4) crystals grown in a viscous polymer solution of poly(acrylic acid) (PAA) was remarkably changed from the tilted columnar assembly into zigzag and helical architectures with increasing PAA concentration. The habit modification of orthorhombic K2SO4 with adsorption of PAA molecules on a specified crystal face fundamentally led to the formation of tilted unit crystals. Concurrently with the habit modification, a diffusion-limited condition controlling the assembly of tilted units was achieved in the presence of PAA molecules in the matrix. Various complex morphologies, including zigzag and helical assembly, emerged through the formation of twinned crystals with the variation of the diffusion condition. Understanding the morphogenesis observed in this report would provide a novel approach for sophisticated crystal design by using an exquisite association of organic and inorganic materials

Selective Preparation of SnO₂ and SnO Crystals with Controlled Morphologies in an Aqueous Solution System

The oxidation state of tin oxide crystals grown in an aqueous solution of Sn(II) was successfully controlled. Rutile-type SnO2 and tetragonal SnO were selectively produced under acidic conditions below pH 3.3 and alkaline conditions above pH 13.1, respectively. The nanostructures, including the grain size and shape, and the mesoscopic assembled states of the crystals were changed with the concentration of the Sn(II) species and a subtle variation of the pH. This versatile fabrication process for functional oxides is based on the difference in the stability of Sn(II) and Sn(IV) depending on the pH in an aqueous solution system

An Experimental Study on the Processes of Hierarchical Morphology Replication by Means of a Mesocrystal: A Case Study of Poly(3,4-ethylenedioxythiophene)

The processes for the synthesis of polymers in a mesocrystal structure were studied for understanding of the mechanisms. The mesocrystal structure has the nanoscale pores between the unit crystals for incorporation of guest molecules. The monomers can be incorporated and polymerized in the nanospace of the mesocrystals. In the present work, a sea urchin spine and poly­(3,4-ethylenedioxythiophene) (PEDOT) were adopted as a model of the original mesocrystal and replicated polymer material, respectively. A sea urchin spine, as an original material, has the hierarchical architectures based on the mesocrystal structure consisting of the oriented carbonate nanocrystals. The monomers were introduced in the nanoscale pores. The composite of the original carbonate and PEDOT was obtained after the incorporation and the polymerization. After dissolution of the original carbonate, the resultant PEDOT architecture showed the hierarchical morphologies similar to those of the original sea urchin spine. The morphology replication processes were compared with those of the different polymers. The important factors for the morphology replication are studied. The present work suggests that the approach can be applied to morphogenesis of a variety of polymer materials

Imaging of Accumulated Mechanical Stresses Using Self-Assembled Layered Conjugated Polymer

When mechanical stresses, such as tensile, compressive, and frictional stresses, are applied to objects by various motions, they are accumulated in materials. Conventional mechanoresponsive materials and sensors detect one-time applied stress. However, the accumulated stresses are not visualized or measured in previous works. The present study demonstrated imaging and sensing of not only one-time but also accumulated tensile, compressive, and frictional stresses. Polyurethane (PU) film was combined with 2D layered polydiacetylene (PDA), a stimuli-responsive color-changing polymer. PDA generally exhibits no color changes with the application of tensile and compression stresses because the molecular motion leading to the color change is not induced by such mechanical stresses. Here the versatile mechanoresponsiveness was achieved using a block copolymer guest partially intercalated in the layered PDA. As the interlayer and outerlayer segments interact with PDA and PU, respectively, the applied stresses to the film are transferred from PU to PDA via the block copolymer guest. The color changes of the film imaged and quantified the accumulated work depending on the number and strength of the applied multiple stresses such as tensile, compressive, and frictional stresses. The design strategy of materials and methodology of sensing can be applied to the development of new sensors for accumulated mechanical stresses in a wide range of length and strength scales

Magnesium-Mediated Nanocrystalline Mosaics of Calcite

Magnesium ions are widely found in calcium-based biominerals as an accessory component. In this report, the influence of magnesium ions on the crystal growth of CaCO3 was investigated on the basis of the nanostructure. The morphology of calcite grown in a supersaturated solution was drastically changed from a regular rhombohedron into a spherical architecture consisting of nanocrystalline mosaics in the presence of a large number of magnesium ions. While magnesium ions were substituted for ca. 6% of calcium ions in the crystal lattice at a maximum, an excess amount of magnesium produced an amorphous phase leading to the nanostructure with modulation of the crystal growth of calcite

Dendritic Growth of NaCl Crystals in a Gel Matrix: Variation of Branching and Control of Bending

A variety of 2D dendritic morphologies, such as orthogonal lattices, oblique lattices, curved weaves, and randomly branching morphologies, of a simple cubic crystal, NaCl, were selectively produced in a thin gel matrix by the tuning of branching growth modes with the variation of NaCl and gelatin concentrations. We characterized the crystal fabric of these specific patterns consisting of NaCl blocks. It is notable that particular curved branches were induced by gradual changes in the growth direction in asymmetric concentration fields. Straight and bending growth in the particular dendrites can be switched by changing the growth velocity in the gel medium

Selective Synthesis of Various Nanoscale Morphologies of Hydroxyapatite via an Intermediate phase

Dicalcium phosphate (DCP) was found to be a suitable precursor for nanoscopically controlled hydroxyapatite (HAp) crystals. Nanoscale needles, fibers, and sheets of HAp were selectively prepared through the hydrolysis of a solid precursor crystal of DCP in an alkali solution by varying the pH and ion concentrations. An oriented array of bundled nanoneedles of HAp elongated in the c axis was obtained under a highly basic condition at pH 11–13. The ordered architecture originated from the spatially periodic nucleation of HAp seeds on the DCP surface through topotactic solid–solid transformation. Long HAp fibers were observed under a relatively mild basic condition at pH 9–10. The fibrous morphology evolved from the nanoneedles produced by the solid–solid transformation with the elongation of the c-axis through a dissolution−precipitation route. Flaky HAp nanosheets consisting of a parallel assembly of nanoneedles were observed with an excess amount of phosphate ions under mild basic conditions. The presence of phosphate ions suppressed the solid–solid transformation and promoted the formation of a two-dimensional structure with the dissolution−precipitation process

Two-Dimensional Conductive and Redox-Active Nanostructures Synthesized by Crystal-Controlled Polymerization for Electrochemical Applications

Two-dimensional nanomaterials have attracted much interest for their anisotropic structures and emergent properties. Whereas a variety of inorganic nanosheets are prepared by exfoliation, design and synthetic strategies of organic nanosheets are still developing. Here we report on crystal-controlled synthesis of conductive and redox-active organic polymer nanosheets with tunable thickness and lateral size. Although the nanosheets consist of classical conductive polymers, such as polypyrrole (PPy) and poly­(3,4-ethylenedioxythiophene) (PEDOT), a new crystal-controlled polymerization approach provides 2D nanomaterials with enhanced and characteristic properties. Oxidative polymerization proceeds on the crystal surface of organic oxidants, such as quinone derivatives, with diffusion of the monomer vapor at low temperature under ambient pressure. The present method affords the control of lateral size and thickness of the nanosheets. The resultant nanosheets show the characteristic and enhanced properties originating from a 2D nature, such as the high structure anisotropy with aspect ratio around 104, enhanced conductivity 287 S cm–1, and specific charge–discharge capacitance 523 F g–1 at the current density of 18 A g–1. The organic nanosheets with conductivity and redox activity can be used as a building block for development of functional materials and devices