Formation Of Hollow Spheres Research Articles

Probing Cooperative Interactions of Tailor-Made Nucleation Surfaces and Macromolecules: A Bioinspired Route to Hollow Micrometer-Sized Calcium Carbonate Particles

It is well known that the formation of biominerals by living organisms is governed by the cooperation of soluble and insoluble macromolecules with peculiar interfacial properties. To date, most of the studies on mineralization processes involve model systems that account only for the existence of one organic matrix and thus disregard the interaction between the soluble and insoluble organic components that is crucial for a better understanding of the processes taking place at the inorganic-organic interface. We have set up a model system composed of a matrix surface, which is composed of a self-assembled monolayer (SAM) and a soluble component, poly(aspartic acid). It could be demonstrated that the phase selection of calcium carbonate and the morphology of the resulting particles are determined by the stabilization of amorphous precursor particles by the polymer and the interaction between polymer and SAM. The morphology of the hollow vaterite microspheres are reminiscent to a 3D analogue of the so-called "coffee-stain effect", where the transformation from a voluminous hydrated, amorphous material to a more dense crystalline material leads to the formation of hollow spheres from massive spherical microparticles.

Fabrication of hollow ZnO microsphere with zinc powder precursor

A facile approach is reported for the preparation of hollow ZnO microspheres using Zn powders as raw materials. Firstly, Zn(OH) 2 was precipitated on the surface of Zn powder to form core/shell structure in solution, and subsequent calcination these core/shell composite particles at 650 °C in air would lead to the formation of ZnO hollow spheres whose diameter were determined by the dimension of the used Zn powder. XRD, TEM, SAED, EDS and UV–vis were used to characterize the as-prepared samples. A formation mechanism is proposed to be a process following the formation of Zn/Zn(OH) 2 core/shell particles, the decomposition of Zn(OH) 2 shell to ZnO, and the sublimation and oxidation of Zn core.

Void formation during early stages of passivation: Initial oxidation of iron nanoparticles at room temperature

The examination of nanoparticles allows study of some processes and mechanisms that are not as easily observed for films or other types of studies in which sample preparation artifacts have been the cause of some uncertainties. Microstructure of iron nanoparticles passivated with iron oxide shell was studied using high-resolution transmission electron microscopy and high-angle annular dark-field imaging in aberration-corrected scanning transmission electron microscopy. Voids were readily observed on both small single-crystal α-Fe nanoparticles formed in a sputtering process and the more complex particles created by reduction of an oxide by hydrogen. Although the formation of hollow spheres of nanoparticles has been engineered for Co at higher temperatures [Y. Yin, R. M. Riou, C. K. Erdonmez, S. Hughes, G. A. Somorjari, and A. P. Alivisatos, Science 304, 711 (2004)], they occur for iron at room temperature and provide insight into the initial oxidation processes of iron. There exists a critical size of ∼8nm for which the iron has been fully oxidized, leading to a hollow iron-oxide nanoparticle. For particles larger than the critical size, an iron/iron-oxide core-shell structure was formed and voids reside at the interface between the oxide shell and the iron core. The present observation provides new insight for tailoring of metal/metal-oxide core-shell structured nanoparticles for applications related to optics, magnetism, and nanoelectronics.

A “User‐Friendly” Chemical Approach Towards Paramagnetic Cobalt Phosphide Hollow Structures: Preparation, Characterization, and Formation Mechanism of Co2P Hollow Spheres and Tubes.

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A “User‐Friendly” Chemical Approach Towards Paramagnetic Cobalt Phosphide Hollow Structures: Preparation, Characterization, and Formation Mechanism of Co2P Hollow Spheres and Tubes

AbstractUser‐friendly chemistry principles have been implemented for the synthesis of hollow Co2P structures. In comparison with the original organometallic approach, the resulting alternative route is safe, simple, and inexpensive. The X‐ray diffraction (XRD) pattern, X‐ray photoelectron spectra (XPS), field emission scanning electron microscope (FESEM) images, and transmission electronic microscope (TEM) images were used to characterize the products, which exhibit paramagnetic behavior down to 2 K, as determined with a commercial superconducting quantum interference device (SQUID) magnetometer. The experimental investigations suggest that the formation of Co2P hollow structures, hollow spheres, and tubes can be explained by an aggregation mechanism and a thermodynamically governed regime. Initially formed Co2P nanoparticles are driven to aggregate into Co2P hollow spheres by the gas bubbles produced. The formation of Co2P tubes then occurs from the hollow spheres via hollow vessels in a thermodynamically governed process. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Layer-by-Layer Assembly of Multiwall Carbon Nanotubes on Spherical Colloids

Multiwall carbon nanotubes (CNTs) have been assembled on various types of colloidal templates using the well-known polyelectrolyte-assisted layer-by-layer (LBL) assembly technique. Dense mono- and multilayers of CNTs were successfully deposited on silica, polystyrene, and melamine spherical colloids of different size, showing that relatively short CNTs completely wrap the surface of the spheres, while long nanotubes stick out of the surface, allowing them to contact various spheres at the same time. Decomposition of the colloidal template leads to formation of hollow CNT spheres, which was demonstrated through treatment of melamine@CNT particles with HCl. The deposition was also carried out on ordered arrays of polystyrene particles, leading to nanostructured, conducting CNT assemblies. Rupture of the assemblies with ultrasound shows that the assembly only takes place on one-half of the colloid spheres, so that “Janus” particles with asymmetric functionalities can be easily prepared.

The formation of gigantic hollow silica spheres from an EO76–PO29–EO76/butanol/ethanol/H2O quaternary system

Download options Please wait... Supplementary files Effect of molar ratio and temperature on product morphology and in-situ monitoring of the gigantic hollow spheres by optical microscopy and SAXS PDF (795K) Article information DOI https://doi.org/10.1039/B413363C Article type Communication Submitted 31 Aug 2004 Accepted 04 Nov 2004 First published 18 Nov 2004 Download Citation J. Mater. Chem., 2005,15, 256-259 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions The formation of gigantic hollow silica spheres from an EO76–PO29–EO76/butanol/ethanol/H2O quaternary system Q. Sun, P. C. M. M. Magusin, B. Mezari, P. Panine, R. A. van Santen and N. A. J. M. Sommerdijk, J. Mater. Chem., 2005, 15, 256 DOI: 10.1039/B413363C To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Qianyao Sun Pieter C. M. M. Magusin Brahim Mezari Pierre Panine Rutger A. van Santen Nico A. J. M. Sommerdijk

A Physical Method of Fabricating Hollow Polymer Spheres Directly from Oil/Water Emulsions of Solutions of Polymers

AbstractSummary: A new physical method of fabricating hollow spheres from different polymers has been developed. In this method, emulsions were prepared by mixing organic solutions of polystyrene, poly(D,L‐lactide‐co‐glycolide) (PLGA), and bacterial poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), water, and surfactants. The evaporation of solvents at room temperature caused a phase separation that eventually yielded hollow spheres. Molecular weights, concentrations of polymers, and the natures of surfactant and solvent were important aspects of hollow sphere formation and structure. A mechanism for the formation of hollow spheres is proposed based on observations made using an optical microscope equipped with a digital camcorder and using scanning electron microscopy images of hollow spheres obtained under different conditions.A scanning electron microscopy image of a broken smaller hollow sphere prepared using a 7 wt.‐% polystyrene solution (diameter of the sphere ∼10 micrometers).magnified imageA scanning electron microscopy image of a broken smaller hollow sphere prepared using a 7 wt.‐% polystyrene solution (diameter of the sphere ∼10 micrometers).

Designing of nanostructured hollow TiO2 spheres obtained by ultrasonic spray pyrolysis.

Theoretical model describing the mechanism of droplet formation and structure of hollow TiO2 spheres prepared by the process of ultrasonic spray pyrolysis, using colloidal solution consisting of the 2.5-nm TiO2 nanoparticles as a precursor, is developed. The proposed model quantitatively defines each line in the size distribution spectrum. The mechanism of droplet formation and/or particle genesis is fully determined by harmonization between the physical fields inherent to the system as the consequence of its physical characteristics: external, e.g., ultrasound, and internal. Agreement between theoretically obtained basic structural parameters (size distribution and geometry) and experimentally determined values was found.

Formation of Hollow Submicrometer Spheres of Nickel Selenides

Abstract Hollow submicrometer spheres of nickel selenides have been successfully prepared via sodium dodecyl sulfate (SDS)-assisted hydrothermal reduction route in which aqueous hydrazine was used as a reducing agent and the surfactant SDS was used as a structure-directing agent.

Facile Synthesis of Hollow Nickel Submicrometer Spheres

Hollow Ni spheres with average diameter of ∼370 nm have been prepared via redox reaction of NiSO4 with NaH2PO2 in a cyclohexane–water–polyglycol emulsion system. It is found that the composition of the reaction system has a significant influence on the formation of hollow Ni spheres. A mechanism of formation of the Ni hollow spheres is proposed.

Self‐Assembly of Polyaniline—From Nanotubes to Hollow Microspheres

AbstractBy simply changing the molar ratio of the dopant to monomer, the morphology of salicylic acid (SA)‐doped polyaniline (PANI) can be changed from one‐dimensional nanotubes (∼ 109–150 nm in diameter) to three‐dimensional hollow microspheres (∼ 1.5–3.1 μm in diameter) via a self‐assembly process. Freeze–fracture electron microscopy (FFEM) proved that hollow spherical micelles composed of SA/aniline act as templates in the formation of either nanotubes or hollow spheres. FTIR and X‐ray diffraction measurements suggest that the hydrogen bond of the –OH group of SA with the amine group of PANI might be a driving force for self‐assembling hollow microspheres, while the hydrogen bond through hydrogen and oxygen of the adjacent SA doped on the polymer chains results in short‐range order of the counter‐ions along the polymer chain in the nanotubes.

Formation of Hollow Spheres of Hydroxyapatite in Plasma Spraying

Hydroxyapatite (HA) particles are subjected to melting at high temperature when used to plasma spray a coating onto a metallic substrate. Accordingly, changes in the melting temperature and morphology of the HA particles are of importance in defining the coating characteristics. The HA particles were plasma sprayed into water and their melting temperature and structure change were analysed using SEM. The results showed that, under the same conditions of spraying, the melting level changed with particle size and more hollow spheres were formed by the molten HA particles, which may have resulted from gaseous P2O5 and H2O arising from decomposed Ca10(PO4)6(OH)2 at a high temperature and also from the volume contraction of HA powder particles as a result of fast cooling. In this study, only the morphology of the HA hollow spheres was examined. These hollow spheres will have important applications in the tissue engineering field and in the optimisation of plasma spraying parameters for HA coatings.

Synthesis of Submicrometer-Sized CdS Hollow Spheres in Aqueous Solutions of a Triblock Copolymer

Submicrometer-sized hollow CdS spheres with a wall thickness of about 20 nm have been synthesized in aqueous solutions of cadmium acetate (Cd(OAc)2) and the triblock copolymer EO20PO70EO20 (P123) at room temperature through the slow release of S2- ions from thioacetamide (TAA). X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), thermogravimetric analysis (TGA), UV−vis absorption, and photoluminescence (PL) spectroscopy have been used for the characterization of the obtained hollow CdS spheres. It has been revealed that a minimum concentration of the polymer P123 was required for the formation of hollow CdS spheres and a double sonication condition was essential for the formation of pure hollow spheres. TEM and dynamic light scattering (DLS) studies have suggested that Cd(OAc)2 could induce P123 to form large complex micelles in the solution but Cd(NO3)2 could not, resulting in the formation of hollow CdS spheres in the acetate system and loose CdS aggregates in the nitrate system. A templating mechanism has been proposed for the production of the hollow CdS spheres; that is, the complex micelles formed by P123 and cadmium acetate acted as soft templates for the precipitation of CdS particles around the surface of the spherical aggregates, leading to the formation of the final hollow spheres.

The Formation of Well‐Defined Hollow Silica Spheres with Multilamellar Shell Structure

Hollow mesoporous silica spheres that are highly defined in shape and size (see Figure) are prepared using a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) [PEO–PPO–PEO] block copolymer based emulsion as the template, and sodium silicate as the silica source. The wall structure of the particles depends on the reaction temperature and can be monitored using small‐angle X‐ray scattering, solid‐state NMR spectroscopy, and cryo‐transmission electron microscopy.

Hollow alumina microspheres prepared by RF thermal plasma

Thermal plasma treatment of ceramic particles of different shape makes them spherical. The spherical particles are hollow or porous under certain experimental conditions. The objective of the present work was to investigate how the water content and porosity of raw materials and the composition of the gas phase influence the size of the hollows. We concluded that the porous structure is the major factor contributing to the formation of hollow spheres, while high initial water content is not a prerequisite for the formation of internal cavities.

Versatile synthesis of nanometer sized hollow silica spherest.

Using the controlled precipitation of silicic acid on functionalized polystyrene latexes, nanometer sized silica-coated spheres could be prepared and subsequently modified to allow dispersion in non-aqueous solvents; removal of the interior polymer by calcination resulted in the formation of hollow silica spheres.

Formation of Silicalite-1 Hollow Spheres by the Self-assembly of Nanocrystals

A simple approach is reported for the preparation of hollow spheres with a 10−20-nm-thick shell of silicalite-1 nanocrystals. The nanocrystals were produced by the steaming of silicalite-1 nanoprecursors (NPs), collected with the help of surfactant from a clear synthesis solution immediately following the induction period. The nanocrystals produced were ≈10−20 nm with a BET surface area of 440−470 m2/g and an external surface area >112 m2/g. A water adsorption isotherm confirmed that the nanocrystals were hydrophobic in nature. These nanocrystals self-assembled into hollow spheres of 100−300-nm diameter when ultrasonicated in ammoniac ethanol.

A flexible route to high strength α-alumina and aluminate spheres

The formation of hollow alumina spheres is accomplished by coating polystyrene beads of 3 μm and 50–80 μm diameter with carboxylic acid functionalized alumina nanoparticles (alumoxanes) from aqueous solution 2–8 wt%. The resulting coated beads were heated to 220°C to calcine the alumoxane to porous amorphous alumina before washing with toluene to remove the polystyrene from inside the ceramic coating. The resulting hollow spheres were sintered at 1000°C to form α-alumina. The α-alumina spheres have been characterized, by SEM (scanning electron microscopy), BET, and hardness measurements, that show the hardness of the hollow alumina sphere (1900 ± 100 Kg.mm−2) approaches that of corundum (ca. 2000 Kg.mm−2). Multilayered bi-phasic spheres may be prepared by subsequent coating the α-alumina spheres with a solution of a metal-doped alumoxane. After calcining, the mixed metal oxide phase (CaAl12O19, Er6Al10O24, MgAl2O4, Al2TiO5, and Y3Al5O12) forms outside of the alumina sphere resulting in a composite like ceramic bi-layer sphere. Pre-formed hollow alumina spheres were incorporated into a resin and ceramic thin film formed from a 1 wt% A-alumoxane aqueous solution. The hardness of the composites is compared to the matrix materials themselves.

Synthesis of Amphiphilic Poly(organosiloxane) Nanospheres with Different Core−Shell Architectures

Core−shell and core−shell−shell nanospheres with different amphiphilicities were synthesized by sequential condensation of trimethoxymethylsilane (T), diethoxydimethylsilane (D), and the functional monomer (chloromethylphenyl)trimethoxysilane (ClBz-T) and mixtures thereof. The condensation was performed in aqueous dispersion in the presence of surfactant. Saturation of reactive surface SiOH groups with monofunctional trimethylsilane monomers prevents interparticle condensation and leads to nanoparticles, which are redispersable in organic solvents. The diameters of the particles range between 20 and 40 nm, depending on the composition. The thickness of the outer, nonfunctionalized shell is determined by asymmetrical flow field−flow fractionation (AF−FFF) and dynamic light scattering (DLS) of the core and core−shell particles, respectively. It varies between 1.5 and 3 nm and is proportional to the volume of added monomer. Incorporating (chloromethylphenyl)siloxane groups in the core and performing a subsequent quaternization reaction of dimethylaminoethanol yield amphiphilic nanospheres with an ionic, hydrophilic core and a hydrophobic outer shell. The amount of ionic moieties is found to be proportional to the amount of functional (chloromethylphenyl)siloxane groups incorporated in the spheres. Additionally, multiple shell topologies were successfully prepared, i.e., particles with a poly(dimethylsiloxane) (PDMS) core, an ionic inner and a hydrophobic outer shell. If linear PDMS chains forming the core are prevented to chemically bind to the inner shell, they may be removed by ultrafiltration, resulting in the formation of hollow spheres.