Hierarchical Hybrid Structure Research Articles

Self-Assembling a Polyoxometalate–PEG Hybrid into a Nanoenhancer To Tailor PEG Properties

The unique performance of natural materials stems from their hierarchical hybrid structures formed through self-assembly. The self-assembly principles of natural materials have been exploited to create artificial materials. Herein, we demonstrate a bottom-up approach that produces polymer nanocomposites as well as a self-assembled nanoenhancer for tailoring the polymer properties. The polymer is a poly(ethylene glycol) (PEG), and the nanoenhancer is aggregates formed by self-assembly of a hybrid. The hybrid is prepared through covalent bonding of a surfactant-encapsulated polyoxometalate (S-POM) complex with a PEG chain and can form aggregates composed of an S-POM complex bilayer sandwiched by two PEG layers. The lateral size of aggregates changes, depending on the conditions used in the sample preparation. Hence, we examined four nanostructures in the solid samples of nanocomposites: hybrid self-assembled nanosheets, PEG crystallized lamellae, PEG/hybrid cocrystallized lamellae, and hybrid crystallized l...

Robust Multi-Layer Hierarchical Model for Digit Character Recognition

Although digit character recognition has got a significant improvement in recent years, it is still challenging to achieve satisfied result if the data contains an amount of distracting factors. This paper proposes a novel digit character recognition approach using a multi-layer hierarchical model, Hybrid Restricted Boltzmann Machines (HRBMs), which allows the learning architecture to be robust to background distracting factors. The insight behind the proposed model is that useful high-level features appear more frequently than distracting factors during learning, thus the high-level features can be decompose into hybrid hierarchical structures by using only small label information. In order to extract robust and compact features, a stochastic 0-1 layer is employed, which enables the model's hidden nodes to independently capture the useful character features during training. Experiments on the variations of Mixed National Institute of Standards and Technology (MNIST) dataset show that improvements of the multi-layer hierarchical model can be achieved by the proposed method. Finally, the paper shows the proposed technique which is used in a real-world application, where it is able to identify digit characters under various complex background images.

A Competitive Electron Transport Mechanism in Hierarchical Homogeneous Hybrid Structures Composed of TiO2 Nanoparticles and Nanotubes

We prepared well-defined hierarchical structures comprising doubly open-ended TiO2 nanotube (NT) arrays covered with various layers of few-nanometer-sized TiO2 nanoparticles (NPs) to investigate the electron collection mechanisms in homogeneous hybrid structures. We found that competitive electron transport pathways (direct transport through the NT and randomized transport through the NPs) are present in the homogeneous hybrid structures. Photoinduced electrons generated at the few-nanometer-sized TiO2 NPs directly connected with TiO2 NTs (e.g., isolated and single-layer NPs on the surface of NTs) dominantly traveled to the NTs. With an increasing number of TiO2 NP layers, photoinduced electrons are randomly transported through the TiO2 NP layers. Enhanced light harvesting and efficient charge collection (∼95%) caused by the increased amounts of dye loading and the direct transport through the NT, respectively, are achieved in a structure with ∼1.4 layers of few-nanometer-sized TiO2 NPs, resulting in a power conversion efficiency of 11.3% with a JSC value (22.9 mA/cm2) close to the theoretical value (∼26 mA/cm2) of a N719-based dye-sensitized solar cell.

One-step synthesis of free-standing α-Ni(OH)2 nanosheets on reduced graphene oxide for high-performance supercapacitors

In this work, a hierarchical hybrid structure of reduced graphene oxide (rGO) supported ultrathin α-Ni(OH)2 nanosheets (denoted as α-Ni(OH)2@rGO NSs) has been developed successfully via an environmentally friendly one-step solution method. The resulting product of α-Ni(OH)2@rGO NSs was further characterized by scanning electron microscope, transmission electron microscope, x-ray diffraction, Raman spectroscopy, x-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller. The ultrathin α-Ni(OH)2 nanosheets of around 6 nm in thickness are uprightly coated on the double sides of rGO substrate. When evaluated as electrodes for supercapacitors, the hybrid α-Ni(OH)2@rGO NSs demonstrate excellent supercapacitor performance and cycling stability, compared with the self-aggregated α-Ni(OH)2 powder. Even after 2000 cycles, the hybrid electrodes still can deliver a specific capacitance of 1300 F g−1 at the current density of 5 A g−1, corresponding to no capacity loss of the initial cycle. Such excellent electrochemical performance should be attributed to the ultrathin, free-standing, and hierarchical nanosheets of α-Ni(OH)2, which not only promote efficient charge transport and facilitate the electrolyte diffusion, but also prevent aggregation of electro-active materials effectively during the charge–discharge process.

Uniquely arranged graphene-on-graphene structure as a binder-free anode for high-performance lithium-ion batteries.

3D graphene interconnected frameworks homogeneously connected with a few-layer graphene film (3DG/FLG) constitute a novel hierarchical hybrid structure for anodes in lithium-ion batteries. The pore-rich 3D graphene network is favorable for Li(+) diffusion and electron transport, and the FLG is a non-metallic current collector that effectively collects/transports charge carriers from/to the 3D graphene network and provides an excellent scaffold to support the 3DG.

Bottom‐Up Hybridization: A Strategy for the Preparation of a Thermostable Polyoxometalate–Polymer Hybrid with Hierarchical Hybrid Structures

AbstractA bottom‐up strategy for the preparation of hierarchical hybrid materials with good thermostability is reported. The hybrid molecule was constructed from a Wells–Dawson‐type polyoxometalate (POM) cluster and a poly(ethylene glycol) (PEG) chain through covalent‐bond formation. The large distinction between the POM cluster and PEG chain results in a microphase separation to form POM and PEG layers that further alternatively arrange into hybrid lamellae with a sub‐20 nm thickness. Then the hybrid lamellae could simultaneously organize into spherulitic superstructures. Because of this hierarchical structuring, strong electrostatic interactions between POM clusters are maximized within the POM layers. This gives rise to thermostability. Structurally, the hybrid lamellae and the superstructures are unchanged, even at 160 °C, and indeed the shear storage modulus of the hybrid material remains nearly constant within this same temperature range. This study demonstrates the concept of bottom‐up hybridization, in which rationally selecting building blocks, designing the hybrid molecule, and then manipulating hierarchical structures can generate thermostable hybrid materials.

A design strategy for the hierarchical fabrication of colloidal hybrid mesostructures.

Advances in nanotechnology depend upon expanding the ability to create new and complex materials with well-defined multidimensional mesoscale structures. The creation of hybrid hierarchical structures by combining colloidal organic and inorganic building blocks remains a challenge due to the difficulty in preparing organic structural units of precise size and shape. Here we describe a design strategy to generate controlled hierarchical organic-inorganic hybrid architectures by multistep bottom-up self-assembly. Starting with a suspension of large inorganic nanoparticles, we anchor uniform block copolymer crystallites onto the nanoparticle surface. These colloidally stable multi-component particles can initiate the living growth of uniform cylindrical micelles from their surface, leading to three-dimensional architectures. Structures of greater complexity can be obtained by extending the micelles via addition of a second core-crystalline block copolymer. This controlled growth of polymer micelles from the surface of inorganic particles opens the door to the construction of previously inaccessible colloidal organic-inorganic hybrid structures.

Enhanced cellular responses to titanium coating with hierarchical hybrid structure

In this work, nano/micro hierarchical hybrid structured surface was prepared by fabricating a titania nanotube layer in plasma sprayed porous titanium coating (TC). In vitro human marrow stem cells (hMSCs) were employed for the evaluation of the biological properties of the anodized titanium coating with a hierarchical structure (HSTC). Significantly higher cell adhesion quantity (about 30% more) was found on the HSTC than that on the as-sprayed TC. The expressions of osteocalcin (OC) and osteopontin (OPN) for the HSTC were also detected to be about twice as high as those on the as-sprayed TC. The enhanced cell responses on the HSTC were explained by the improved protein adhesion resulted from the increased surface area and surface energy. Combining the advantages in the mechanical fixation and long-term stability of the plasma sprayed porous TC, the HSTC with a hierarchical structure may be a good candidate for hard tissue replacements, especially for load-bearing implants.

Epoxy-silica hybrids by nonaqueous sol–gel process

The epoxy-silica hybrids have been prepared by the non-aqueous sol–gel process and the in situ generation of nanosilica from tetraethoxysilane was initiated with borontrifluoride monoethylamine (BF3MEA). The DGEBA based epoxy networks with aliphatic, cycloaliphatic and aromatic amines were used as matrices. The solventless technique made it possible to avoid drawbacks of the classical aqueous procedure. The “non-aqueous” systems show improved homogeneity and thermomechanical properties in particular at the application of the coupling agent glycidyloxypropyl trimethoxysilane. Mechanism of the non-aqueous sol–gel process under BF3MEA action and evolution of the hybrid structure during polymerization, followed by chemorheology, are discussed. The nanosilica structure growth is slower under the non-aqueous procedure thus facilitating a better structure control. The hybrids with both particulate and bicontinuous morphologies were prepared and the epoxy-silica interphase bonding and crosslinking through the formed silica domains was proved. The hybrid hierarchical structure and morphology were determined by NMR, SAXS, TEM and DMA.

Synthesis and Optical Properties of Mesoporous β‐Co(OH)2/Brilliant Blue G (G250) Hybrid Hierarchical Structures

New mesoporous β-Co(OH)(2) /brilliant blue G (G250) hybrid hierarchical structures constructed by thin mesocrystal nanosheets can be synthesized by a one-step refluxing process under the synergistic effect of CTAB and G250. This approach opens up an avenue to access new novel inorganic/dye hybrid materials with hierarchical structures for pigment and electrocatalytic application.

Fabrication of hierarchical hybrid structures using bio‐enabled layer‐by‐layer self‐assembly

Development of versatile and flexible assembly systems for fabrication of functional hybrid nanomaterials with well-defined hierarchical and spatial organization is of a significant importance in practical nanobiotechnology applications. Here we demonstrate a bio-enabled self-assembly technique for fabrication of multi-layered protein and nanometallic assemblies utilizing a modular gold-binding (AuBP1) fusion tag. To accomplish the bottom-up assembly we first genetically fused the AuBP1 peptide sequence to the C'-terminus of maltose-binding protein (MBP) using two different linkers to produce MBP-AuBP1 hetero-functional constructs. Using various spectroscopic techniques, surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR), we verified the exceptional binding and self-assembly characteristics of AuBP1 peptide. The AuBP1 peptide tag can direct the organization of recombinant MBP protein on various gold surfaces through an efficient control of the organic-inorganic interface at the molecular level. Furthermore using a combination of soft-lithography, self-assembly techniques and advanced AuBP1 peptide tag technology, we produced spatially and hierarchically controlled protein multi-layered assemblies on gold nanoparticle arrays with high molecular packing density and pattering efficiency in simple, reproducible steps. This model system offers layer-by-layer assembly capability based on specific AuBP1 peptide tag and constitutes novel biological routes for biofabrication of various protein arrays, plasmon-active nanometallic assemblies and devices with controlled organization, packing density and architecture.

Enhanced acetone sensing performances of hierarchical hollow Au-loaded NiO hybrid structures

Hierarchical hollow Au-loaded NiO hybrid microspheres have been synthesized with good uniformity by a surfactant-free hydrothermal route and subsequent heat treatment. This method requires high concentrations of a nickel precursor (0.2 M) and introduction of a trace amount of Au nanoparticles into the reaction system. The hierarchical hollow Au-loaded NiO hybrid microsphere comprises several nanorods and nanosheets. To demonstrate the usage of such hierarchical hybrid nanomaterials, a gas sensor has been fabricated from the as-synthesized Au-loaded NiO microspheres and investigated for acetone detection. The Au-loaded NiO sensor exhibits significantly improved sensing performances in terms of high sensitivity, low detection limit, better selectivity, rapid response, and good reproducibility in comparison with pure NiO. The effects of Au loading on the acetone-sensing properties of hierarchical NiO microspheres have been investigated.

Influence of hierarchical hybrid micro/nano-structured surface on biological performance of titanium coating

In this article, hierarchical hybrid micro/nano-structured titanium surface was obtained by alkali treating the vacuum plasma sprayed titanium coating following hot water immersing for 24 h. The influences of the surface microstructure on the in vitro and in vivo biologic performance of titanium coating were studied. Human bone marrow-derived stromal cells (hBMSCs) were used for in vitro cytocompatibility evaluation. Compared with the rough titanium coating surface, cell behaviors, such as spread and proliferation were apparently enhanced by mimicking the hierarchical hybrid structure of bone tissue, while ALP expression was lower at days 4 and 7. With the expanding of induction time, the ALP activity rapidly increased on the hierarchical surface. After 10 days induction, it became much higher than that on the rough titanium surface. A canine model was applied for an in vivo evaluation of the bone bonding ability. Histologic examination demonstrated that new bone was formed more rapidly on the hierarchical surface implants than that on the rough titanium surface. All these results indicate that the hierarchical surface is favorable for the response of hBMSCs and early bone bonding.

Porous silica spheres in macroporous structures and on nanofibres

Porous nanospheres have a wide range of applications such as in catalysis, separation and controlled delivery. Among these nanospheres, syntheses and applications of porous silica nanospheres have been investigated extensively. Uniform porous silica nanospheres can be synthesized using a modified Stöber method. In the present study, porous silica spheres were prepared in the pre-formed emulsion-templated porous polyacrylamide (PAM). A hierarchical hybrid structure of mesoporous silica spheres was formed in the highly interconnected macroporous polymer. The polymer scaffold could be removed by calcination with porous silica spheres and the macroporous structures retained. This resulted from the close packing or aggregation of small silica nanospheres in the pores and on the surface of pores of PAM. The modified Stöber synthesis was further carried out in pre-formed polymer nanofibres (chitosan and sodium carboxymethyl cellulose). The structure of porous silica spheres on nanofibres was produced in the presence of the polymer or composite fibres. The corresponding inorganic structures were successfully obtained after calcination. The hierarchical structures of porous nanospheres within macroporous structures or on nanofibres are of potential interest to researchers in nanomaterials, porous polymers, supported catalysis and controlled delivery.

Photochemical Behavior of High Quantum Yield SWNTs Functionalized with Anthracene Salts

Two different fluorescent single walled carbon nanotubes (SWNT) were prepd. First by a reaction of oxidized SWNT-K salt with 1,3-bis(9-anthracenylmethyl)imidazolium chloride (bamim)Cl to provide a fluorescent system SWNT-(bamim), via ion exchange and formation of KCl. Second, by phys. mixing of non-functionalized SWNTs with (bamim)Cl salt to provide SWNT/[bamim]Cl in which anthracene units adhere to the walls of the nanotube via π-π stacking interactions. The SWNT-[bamim] material exhibits a partially reversible photodimerization process that was investigated using UV/Vis spectroscopy, fluorescence emission spectroscopy, and HR-TEM. This study establishes the concept of photoinduced/photoswitchable org.-SWNT conjugated systems based on anthracene dimerization as a prototypical reaction. Hierarchical nanoscale hybrid structures based on the above materials and an understanding of their optical properties may facilitate the construction of SWNT based materials.

A framework of fuzzy hybrid systems for modelling and control

This paper presents a new approach to modelling and control of hybrid systems with both continuous variables and discrete events. Applying the fuzzy set theory, a hierarchical fuzzy hybrid structure consisting of a fuzzy discrete event dynamic system and a continuous variable dynamic system is constructed, which not only captures the hybrid continuous/discrete dynamics but also handles the uncertainties in states and state transitions. The identification of continuous and discrete components is developed, and the hybrid control is then synthesised by fuzzy IF–THEN rules embedded in the fuzzy interface. An example of the optimisation of a production line in manufacturing shows the efficacy of the proposed approach.