Robust superhydrophobicity of hierarchical ZnO hollow microspheres fabricated by two-step self-assembly

Superhydrophobic and superhydrophilic surfaces have been extensively inves- tigated due to their importance for industrial applications. It has been reported, however, that superhydrophobic surfaces are very sensitive to heat, ultraviolet （UV） light, and electric potential, which interfere with their long-term durability. In this study, we introduce a novel approach to achieve robust superhydrophobic thin films by designing architecture-defined complex nanostructures. A family of ZnO hollow microspheres with controlled constituent architectures in the morphologies of 1D nanowire networks, 2D nanosheet stacks, and 3D mesoporous nanoball blocks, respectively, was synthesized via a two-step self-assembly approach, where the oligomers or the constituent nanostructures with specially designed structures are first formed from surfactant templates, and then further assembled into complex morphologies by the addition of a second co-surfactant. The thin films composed of two-step synthesized ZnO hollow microspheres with different architectures presented superhydrophobicities with contact angles of 150°-155°, superior to the contact angle of 103° for one-step synthesized ZnO hollow microspheres with smooth and solid surfaces. Moreover, the robust superhydrophobicity was further improved by perfluorinated silane surface modification. The perfluorinated silane treated ZnO hollow microsphere thin films maintained excellent hydrophobicity even after 75 h of UV irradiation. The realization of environmentally durable promising solution for their long-term irradiations. superhydrophobic surfaces provides a service under UV or strong solar light     

Hollow hydroxyapatite microspheres as a device for controlled delivery of proteins

Hollow hydroxyapatite (HA) microspheres were prepared by reacting solid microspheres of Li₂O–CaO–B₂O₃ glass (106–150 μm) in K₂HPO₄ solution, and evaluated as a controlled delivery device for a model protein, bovine serum albumin (BSA). Reaction of the glass microspheres for 2 days in 0.02 M K₂HPO₄ solution (pH = 9) at 37°C resulted in the formation of biocompatible HA microspheres with a hollow core diameter equal to 0.6 the external diameter, high surface area (~100 m²/g), and a mesoporous shell wall (pore size ≈13 nm). After loading with a solution of BSA in phosphate-buffered saline (PBS) (5 mg BSA/ml), the release kinetics of BSA from the HA microspheres into a PBS medium were measured using a micro bicinchoninic acid (BCA) protein assay. Release of BSA initially increased linearly with time, but almost ceased after 24–48 h. Modification of the BSA release kinetics was achieved by modifying the microstructure of the as-prepared HA microspheres using a controlled heat treatment (1–24 h at 600–900°C). Sustained release of BSA was achieved over 7–14 days from HA microspheres heated for 5 h at 600°C. The amount of BSA released at a given time was dependent on the concentration of BSA initially loaded into the HA microspheres. These hollow HA microspheres could provide a novel inorganic device for controlled local delivery of proteins and drugs.     

Hollow MCM-41 microspheres derived from P(St-MMA)/MCM-41 core/shell composite particles

In soap-free latex media, poly(styrene-methyl methacrylate)/MCM-41 core/shell composite microspheres have been fabricated by adding silicate source in batches. In this process, silicate species and the surfactant micelles were self-assembled into 2-dimensional hexagonal arrangement on the surface of P(St-MMA) microspheres. Hollow MCM-41 microspheres were obtained via removing polymer core by solvent. XRD, TEM, IR and N₂ adsorption-desorption analysis were applied to characterize products. The results showed that average diameter and wall thickness of hollow MCM-41 microspheres is about 240 nm and 20 nm, respectively. Results of N₂ adsorption-desorption indicate that hollow MCM-41 microspheres possess a highly ordered mesoporous structure and a narrow pore distribution with a mean value of 2.34 nm.     

Short- and long-term structural properties of pultruded beam assemblies fabricated using adhesive bonding

Two beam assemblies fabricated using simple pultruded sections and adhesive bonding have been tested to determine their structural properties. The test configuration was three-point bending to simulate the most severe loading in a proposed application. Short-term stiffnesses are compared with those predicted using known section properties and linear elastic beam theory. Accelerated creep test data are used to determine long-term behaviour using Findley's linear viscoelastic theory. For the purpose of structural design, Findley's model is used to estimate the increase in maximum deflection due to a constant design loading of 1 week, 1 year and 10 years.     

Hollow carbonated hydroxyapatite microspheres with mesoporous structure: Hydrothermal fabrication and drug delivery property

Hollow carbonated hydroxyapatite microspheres with mesoporous structure (HCHAs) have been fabricated by using calcium carbonated microspheres as sacrificial templates according to the following routes: (i) the in situ deposit of carbonated hydroxyapatite on the surfaces of CaCO₃ microspheres by hydrothermal method and (ii) the removal of CaCO₃ by chemical etching. The HCHAs consist of a hollow core and a mesoporous shell. Interestingly, the shell of the microspheres is constructed by carbonated hydroxyapatite nanoplates as building blocks. Moreover, these nanoplates are composed of many smaller nanoparticles with different crystal orientations, and the mesopores exist among these nanoparticles. The HCHAs exhibit the high drug-loading capacity and sustained drug release property, suggesting that the hierarchically porous microspheres have great potentials for bone-implantable drug-delivery applications.     

Barium titanate fabricated from fur-fibres

Long-fibrous barium titanate (BaTiO₃) particles were prepared by a hydrothermal reaction of potassium titanate hydrate (2K₂O·11TiO₂·3H₂O) and barium hydroxide (Ba(OH)₂). Effects of preparation conditions on crystal structure and powder morphology were examined. Fur-fibres of K₂O·4TiO₂, 1–10 mm long and 1–100 m in diameter, were obtained by heating a mixture of K₂CO₃ and TiO₂ powders at 1000 C for 100 h. Keeping the fur-fibres in ion-exchanged water for 4 days gave fur-fibres of 2K₂O·11TiO₂·3H₂O). Long-fibrous BaTiO₃, with fibres 100m–1mm long and 1–10 m in diameter, was obtained by a hydrothermal reaction of the hydrate and Ba(OH)₂ (Ba/Ti ratio of 1) at 150 C for 24 h. As-prepared long-fibrous BaTiO₃ was composed of fine crystallites (average size about 270 nm) of cubic phase. The cubic phase and morphology of fur-fibres were maintained up to 1250 C, but heat treatment at 1300 C brought about a growth of crystallites to a few micrometers and a phase transformation to tetragonal phase. It was found that the hydrothermal reaction was effective in producing crystalline BaTiO₃ powder at a low temperature of 150 C.     

Hollow microspheres with binary colloidal and polymeric membrane: Effect of polymer and particle concentrations

We report here the preparation of hollow microspheres with a binary shell structure consisting of a precipitated polymer film with a layer of colloidal particles embedded on its outer surface. We recently demonstrated a method for the preparation of microspheres from solid-stabilised emulsion templates using various colloidal particle systems as emulsifiers. In the present work we use colloidal silica as an emulsifier for the preparation of the emulsion template for the microspheres and study the effect of polymer and particle concentrations on the obtained structures.Observations using optical microscopy showed that decreasing the polymer concentration led to a reduction in the capsule wall thickness and apparent strength of the microspheres when dried. Importantly, all microspheres preserved their integrity when in suspension. SEM studies confirmed the differences observed in the thickness of the precipitated film at the oil/water interface. In addition, we also demonstrate that a larger particle concentration leads to microspheres with a lower degree of porosity.     

Semiconductor devices fabricated from actinide oxides

Recent investigations of the semiconductive properties of urania indicate that the oxides of uranium may be useful in the fabrication of certain active electronic devices. UO₂ and U₃O₈ have been characterized as to their photo-optical properties and active devices have been fabricated from urania.     

Hollow polypyrrole/Ni/PVDF microspheres for broadband microwave absorption via a spray phase inversion method

Journal of Materials Science - There is growing interest in porous multi-component composites as efficient electromagnetic wave absorption (EMWA) materials at microwave frequencies. Herein, a novel...     

Hollow polymer microspheres containing a gold nanocolloid core adsorbed on the inner surface as a catalytic microreactor

Hollow polymer microspheres with different polarity and functional group for the shell layer containing gold nanocolloid cores adsorbed on the inner surface were prepared by selective removal of sandwiched silica layer from the corresponding gold/silica/polydivinylbenzene (Au/SiO₂/PDVB), Au/SiO₂/poly(ethyleneglycol dimethacrylate) (Au/SiO₂/PEGDMA), and Au/SiO₂/poly(ethyleneglycol dimethacrylate-co-methacrylic acid) (Au/SiO₂/P(EGDMA-co-MAA) tri-layer microspheres, respectively. The tri-layer microspheres were synthesized by distillation precipitation polymerizations of divinylbenzene (DVB), ethyleneglycol dimethacrylate (EGDMA), EGDMA together with methacrylic acid (MAA) in presence of 3-(methacryloxy)propyltrimethoxysilane (MPS)-modified gold/silica (Au/SiO₂) core–shell particles as seeds, which were prepared by coating of a layer of silica onto the surface of Au nanocolloids with the aid of polyvinylpyrrolidone (PVP) via a modified Stöber method. The catalytic property and stability as a microreactor of the hollow polymer microspheres with Au nanocolloid cores adsorbed on the inner surface were studied by the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AnP) with sodium borohydride (NaBH₄) as reductant. Transmission electron microscopy (TEM) and Fourier transform infrared spectra (FT-IR) were used for characterizing the morphology and structure of the resultant microspheres.     

Monodisperse carbon microspheres synthesized from asphaltene

Carbon microspheres were synthesized from asphaltene by a chemical vapor deposition (CVD) method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy method. The results indicated the monodispersed spheres were almost curving graphitic structure with diameters from 300 to 400 nm. G mode centre of carbon microspheres had shifted upward compared with graphite. As an efficient precursor, asphaltenes were metastable structures at higher temperature. The aromatic carbon rings of asphaltenes promoted the formation of closed cage graphitic structures. The results provide a new perspective for the application of asphaltene.     

Electroluminescence from silicon nanoparticles fabricated from the gas phase

Electroluminescence from as-prepared silicon nanoparticles, fabricated by gas phase synthesis, is demonstrated. The particles are embedded between an n-doped GaAs substrate and a semitransparent indium tin oxide top electrode. The total electroluminescence intensity of the Si nanoparticles is more than a factor of three higher than the corresponding signal from the epitaxial III-V semiconductor. This, together with the low threshold voltage for electroluminescence, shows the good optical properties of these untreated particles and the efficient electrical injection into the device. Impact ionization by electrons emitted from the top electrode is identified as the origin of the electrically driven light emission.     

粗细粉混用法制备堇青石膜支撑体

将粒径分别为1.5和25μm的堇青石粉体按一定比例球磨混匀,添加适当的粘结剂和造孔剂,经捏合、陈腐、挤出成型及烘坯处理后,程序升温至一定温度烧结2h制备膜支撑体.结果表明,细粉含量20%(质量分数)、1400℃烧结所得的支撑体综合性能较好:钝水通量为10.3m3/(m2·h);爆破压力为2.21MPa.其浸渍于5%(质...     

Single-mode optical waveguides fabricated from fluorinated polyimides

Buried channel optical waveguides were fabricated from fluorinated polyimides. They operated in single mode and showed an optical loss of less than 0.3 and 0.7 dB/cm for TE and TM polarizations, respectively, at a wavelength of 1.3 mum. Moreover, these waveguides had high heat and moisture resistance; the optical loss did not significantly change after heating at 380 degrees C for 1 h or after exposure to 85% relative humidity at 85 degrees C for over 200 h.     

Fiber-reinforced composite foam from expandable PVC microspheres

The properties of composite foam based on PVC expandable microspheres reinforced with continuous aramid fibers are described. The foam was fabricated by infiltrating low-density non-woven fiber webbing with PVC microspheres. The assembly was subsequently heated to expand the foam. The resulting composite foam consisted of 10 wt% aramid fibers and had a density of 100 kg/m³. Mechanical properties, crack propagation, and microstructure of composite foams were evaluated and compared with properties of similar unreinforced foam and with commercial PVC foam of comparable density. The influence of fiber concentration, fiber architecture and bonding was investigated also. Properties were measured in tension, shear, compression, and flexure using standard ASTM test methods. The composite foam performance equaled or surpassed the performance of most thermoplastic foams commercially available. The tensile strength and modulus of the composite foam increased by factors of 6 and 8, respectively, and the shear strength and modulus increased by factors of 1.8 and 2.4. The composite foam also exhibited improved strain energy density and damage tolerance, and reduced notch sensitivity.     

胶体晶体模板法合成有序大孔聚甲基丙烯酸甲酯

以离心沉降技术组装的二氧化硅胶体晶体为模板,从同种尺寸的二氧化硅微球出发,合成了孔的结构和形貌不同的两种有序大孔聚甲基丙烯酸甲酯。采用扫描电镜对模板、复合物及聚合物的形貌和微观结构进行了观察和表征。实验结果表明,所合成的聚甲基丙烯酸甲酯具有高度有序的多孔结构,模板的热处理工艺对孔的形状和连通性均有重要影响。     

Hollow TiO2:Sm3+ spheres with enhanced photoluminescence fabricated by a facile method using polystyrene as template

Uniform hollow Sm³⁺-doped titania phosphors were prepared via a facile method using polystyrene spheres as template. After calcination at 500 °C for 3 h, hollow TiO₂:Sm³⁺ spheres with outer diameters of approximately 250 nm and a shell thicknesses ranging from 50 to 70 nm were obtained. A possible formation mechanism of the evolution process of the spheres was discussed in this paper. Photoluminescence (PL) results showed that the emission intensity of the as-prepared hollow TiO₂:Sm³⁺ spheres was 2.1 times higher than that of amorphous nanoparticles (NPs). We propose that this PL enhancement is due to the unique hollow structures obtained.     

Green light stimulates terahertz emission from mesocrystal microspheres

The discovery of efficient sources of terahertz radiation has been exploited in imaging applications, and developing a nanoscale terahertz source could lead to additional applications. High-frequency mechanical vibrations of charged nanostructures can lead to radiative emission, and vibrations at frequencies of hundreds of kilohertz have been observed from a ZnO nanobelt under the influence of an alternating electric field. Here, we observe mechanical resonance and radiative emission at ～ 0.36 THz from core-shell ZnO mesocrystal microspheres excited by a continuous green-wavelength laser. We find that ～ 0.016% of the incident power is converted into terahertz radiation, which corresponds to a quantum efficiency of ～ 33%, making the ZnO microspheres competitive with existing terahertz-emitting materials. The mechanical resonance and radiation stem from the coherent photo-induced vibration of the hexagonal ZnO nanoplates that make up the microsphere shells. The ZnO microspheres are formed by means of a nonclassical, self-organized crystallization process, and represent a straightforward route to terahertz radiation at the nanoscale.