Hierarchical Microarchitectures Research Articles

A Model of Sheath of Bovine Horn Coupled Nano-Mechanical Properties and Microstructures

With the long-term evolution, the bovine horn as the primary protective and offensive weapon has superior mechanical properties. The bovine horn consists of two parts, the keratinous horn sheath and the bony core. The keratinous is natural composite material with a highly toughness and can bear impact and repeated loads during fighting. It has a complex hierarchical microarchitecture. To establish the qualitative model for finding the possible relationship between structure and mechanical properties of bovine horn, in this paper, the model was established that based on the parameters provided by microstructure imaging and nanoindentation testing from transverse and longitudinal directions. Which would provide information useful for the developing bionic composite materials for micro-aircraft, bionic tribology, bionic medical apparatus and bionic organs (tissue engineering).

Are all osteocytes equal? Multiscale modelling of cortical bone to characterise the mechanical stimulation of osteocytes

Bone continuously adapts its internal structure to accommodate the functional demands of its mechanical environment. This process is orchestrated by a network of mechanosensitive osteocytes that respond to external mechanical signals and recruit osteoblasts and osteoclasts to alter bone mass to meet loading demands. Because of the irregular hierarchical microarchitecture of bone tissue, the precise mechanical stimuli experienced by osteocytes located in different regions of the tissue is not well-understood. The objective of this study is to characterise the local stimulus experienced by osteocytes distributed throughout the tissue structure. Our models predict that an inhomogeneous microstructural strain field contributes to osteocytes receiving vastly different stimuli at the cellular level, depending on their location within the microstructure. In particular, osteocytes located directly adjacent to micropores experienced strain amplifications in their processes of up to nine times the applied global strain. Furthermore, it was found that the principal orientation of lamellar regions was found to contribute significantly to the magnitude of the stimulus being received at the cellular level. These findings indicate that osteocytes are not equal in terms of the mechanical stimulus being received, and we propose that only a subset of osteocytes may be sufficiently stimulated to function as mechanoreceptors.

Rationally Designed Complex, Hierarchical Microarchitectures

The emergence of complex nano- and microstructures is of fundamental interest, and the ability to program their form has practical ramifications in fields such as optics, catalysis, and electronics. We developed carbonate-silica microstructures in a dynamic reaction-diffusion system that allow us to rationally devise schemes for precisely sculpting a great variety of elementary shapes by diffusion of carbon dioxide (CO2) in a solution of barium chloride and sodium metasilicate. We identify two distinct growth modes and show how continuous and discrete modulations in CO2 concentration, pH, and temperature can be used to deterministically switch between different regimes and create a bouquet of hierarchically assembled multiscale microstructures with unprecedented levels of complexity and precision. These results outline a nanotechnology strategy for "collaborating" with self-assembly processes in real time to build arbitrary tectonic architectures.

Hydrothermal synthesis of meso/macroporous BiVO4 hierarchical particles and their photocatalytic degradation properties under visible light irradiation

An ordered hierarchical meso/macroporous monoclinic bismuth vanadate (BiVO4) particle was fabricated for the first time by a simple two-step melamine template hydrothermal method followed by calcination. The physiochemical parameters of as-prepared porous materials were characterized by means of X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Raman, Barrett-Emmett-Teller, and UV-vis techniques. The nitrogen adsorption-desorption measurement and pore size distribution curve suggest that meso/macropores exist in these hierarchical microarchitectures. Further, it is found that melamine plays a significant role in the formation of porous BiVO4 particles, and when a known amount of melamine was added, the surface area and pore size of such porous BiVO4 particles were increased. The photocatalytic activities of the as-prepared hierarchical BiVO4 samples were measured for the photodegradation of Congo red aqueous dye solution under visible light irradiation. Surprisingly, the porous BiVO4 particles showed outstanding photocatalytic activities than polycrystalline BiVO4 sample. The possible enhancement of such catalytic performance has also been further discussed.

Hierarchical microarchitectures of AgGa1−xInxS2: Long chain alcohol assisted synthesis, band gap tailoring and photocatalytic activities of hydrogen generation

An enhanced visible-light-driven photocatalyst, AgGa1−xInxS2, was prepared by a facile long chain alcohol assisted hydrothermal route. Phase structures, morphologies, optical properties, energy level and specific surface areas of the products were characterized by X-ray diffraction, scanning electron microscope, UV–vis spectra and BET analysis. The obtained products show unique hierarchical microarchitectures which were fabricated by micro-sphere and nano-sheets. The introducing of long chain alcohol (pentanol and heptanol) was investigated to be crucial for the forming of hierarchical microarchitectures. On the other hand, the band gap energy of AgGa1−xInxS2 (x = 0–1) estimated from the onset of absorption edge was found to be reduced from 2.71 eV (x = 0) to 1.93 eV (x = 1) by indium substitution. The photocatalytic activity for hydrogen evolution was investigated under visible light irradiation (λ > 400 nm). The rate of hydrogen evolution reached up to 813 μmol/h when the amount of In (x) was 0.1 and the roles of long chain alcohol and Ga/In were also carefully investigated.

ChemInform Abstract: Hierarchical Structure and Mechanical Properties of Nacre: A Review

AbstractReview: 123 refs.

Hydrothermal synthesis and tunable luminescence of persimmon-like sodium lanthanum tungstate:Tb3+, Eu3+ hierarchical microarchitectures

Persimmon-like NaLa(WO4)2 microarchitectures were prepared via hydrothermal process with using trisodium citrate (Na3Cit) as chelated reagent and characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), photoluminescence (PL), and fluorescent dynamics. The influences of Na3Cit concentration, organic additivities, and reaction time on the morphologies of NaLa(WO4)2 phosphor were studied. The results revealed that Na3Cit species had double functions of strong ligand and structure-directing reagent that could efficiently control the formation of persimmon-like NaLa(WO4)2 microarchitectures. The possible mechanism for the growth of persimmon-like NaLa(WO4)2 microarchitectures was attributed to the Ostwald ripening mechanism. The energy transfer from Tb3+ to Eu3+ in the persimmon-like NaLa(WO4)2 phosphors was observed. The energy transfer efficiencies and emission colors can be tuned by changing the concentration of Eu3+. Finally, it was deduced that the electric dipole–dipole interaction (D–D) is the main mechanism for energy transfer between Tb3+ and Eu3+ in the persimmon-like NaLa(WO4)2 phosphor.

ZnO nanosheet-based hierarchical microarchitectures for enhanced conversion efficiency in dye-sensitized solar cells

Hierarchical ZnO microarchitectures have been fabricated on a large scale by a simple and economical citrate-mediated hydrothermal route for application in dye-sensitized solar cells (DSSCs). These flowerlike architectures are constructed by many interleaving nanosheets which have ultrathin thickness of about 5 nm. Compared with the DSSCs based on other forms of nanostructures, such as ZnO nanorods and nanoparticles, the DSSCs constructed by these hierarchical ZnO microarchitectures demonstrate a remarkable enhancement in photoelectric conversion efficiency. This enhanced performance is mainly due to the large surface area of the hierarchical microarchitectures for dye loading, and their special structural feature to ensure rapid transportation of electrons. Our results suggest that this new type of ZnO nanosheet-based microarchitectures is a promising material for application in DSSCs.

Hierarchical structure and mechanical properties of nacre: a review

Nacre (known as mother of pearl) is the iridescent inner shell layer of some mollusks. Nacre is composed of 95 wt% aragonite (a crystallographic form of CaCO3) and 5 wt% organic materials (proteins and polysaccharides). It is well known that it exhibits high fracture toughness, much greater than that of monolithic aragonite, because of its ingenious structure. It also exhibits energy absorption properties. It has a complex hierarchical microarchitecture that spans multiple length scales from the nanoscale to the macroscale. It includes columnar architectures and sheet tiles, mineral bridges, polygonal nanograins, nanoasperities, plastic microbuckling, crack deflection, and interlocking bricks, which exhibit a remarkable combination of stiffness, low weight and strength. Nacre's special self-assembly characteristics have attracted interest from materials scientists for the development of laminated composite materials, molecular scale self-assembly and biomineralization. This paper reviews the characteristics of hierarchical structure and the mechanical properties of nacre that provide the desired properties, and the latest developments and biomimetic applications.

Mesoporous SrF2 and SrF2:Ln3+ (Ln = Ce, Tb, Yb, Er) Hierarchical Microspheres: Hydrothermal Synthesis, Growing Mechanism, and Luminescent Properties

Uniform and well-dispersed SrF2 hierarchical microspheres have been successfully synthesized by a facile and friendly hydrothermal method. The experimental results indicate that such 3D hierarchical SrF2 microspheres with size about 1 μm are assembled by numerous nanocrystals (about 100 nm). Nitrogen adsorption−desorption measurement suggests that mesopores exist in these hierarchical microarchitectures. The formation process of the hierarchical SrF2 microspheres and luminescence properties of SrF2:Ln3+ (Ln = Ce, Tb, Yb, Er) microspheres have been investigated in detail. It is found that reaction time and trisodium citrate play a key role in forming the hierarchical microspheres. In addition, the lanthanide ions (Ln3+)-doped SrF2 hierarchical microspheres show strong green (Ln3+ = Ce3+, Tb3+) photoluminescence with 45% quantum efficiency and cathodoluminescence centered at 542 nm corresponding to the 5D4 → 7F5 transition of Tb3+ under excitation of ultraviolet light and low-voltage electron beam, respectively. In addition, SrF2:Yb3+,Er3+ hierarchical microspheres show bright yellow upconversion emission under 980 nm laser diode excitation. The as-synthesized SrF2:Ln3+ luminescent microspheres might find some potential applications in areas of photoluminescence and field emission displays.

Hydrothermal Synthesis of Mesoporous InVO4 Hierarchical Microspheres and Their Photoluminescence Properties

In this work, uniform InVO4 hierarchical microspheres with the assistance of sodium dodecyl benzene sulfonate (SDBS) have been successfully synthesized by a facile hydrothermal method. X-ray diffraction, X-ray photoelectron spectra, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction were used to characterize the as-synthesized samples. The results indicate that such 3D hierarchical architecture InVO4 microspheres are polycrystalline and assembled by numerous nanocrystals. Nitrogen adsorption-desorption measurement and the pore size distribution curve suggest that mesopores exist in these hierarchical microarchitectures. The formation mechanism has been proposed based on Oswald ripening and nonoriented attachment. It is further found that SDBS plays a key role in the formation process, and when the amount of SDBS is adjusted, the average diameter of such InVO4 microspheres could be controlled from 5 to 1 microm. UV-vis diffuse reflectance and PL spectra are employed to estimate the photoluminescence property of as-prepared InVO4 samples.