Formation Of Hollow Microspheres Research Articles

Mechanisms of Forming Hollow Microspheres from Solid Granules

Problems in fabrication of large-size hollow microspheres with specific properties and ideal geometric parameters for inertial confinement fusion and other applications require profound knowledge of their formation processes. In this work, we analyze experimentally and analytically the formation of hollow microspheres from solid spherical granules by high-temperature foaming and formulate the conditions for fabrication of microcapsules with high parameters in high-temperature processes.

Stability of Soluble Dialdehyde Cellulose and the Formation of Hollow Microspheres: Optimization and Characterization

The poor solubility of raw cellulose greatly limits its applications. Herein, the periodate oxidation of cellulose was conducted to obtain dialdehyde cellulose (DAC), which is a kind of soluble and...

Investigation of Hollow Microspheres Obtained in Thermal Plasma Jet Using Ash-Slag Wastes from CHP in Kemerovo Oblast

The processes occurring during the formation of hollow microspheres in a thermal plasma jet on the basis of ash-slag waste from CHP in Kemerovo Oblast are studied. The results of physical and chemical studies (scanning electron microscopy, energy-dispersive x-ray and infrared spectroscopy) of the initial raw material and the obtained microspheres based on it are presented. A comparative analysis is performed of hollow microspheres obtained by the conventional method in batch-type furnaces at CHP in Kemerovo Oblast and microspheres obtained using thermal plasma.

Emulsion Templating Cyclic Polymers as Microscopic Particles with Tunable Porous Morphology.

Cyclic polymers are a particular class of macromolecules without terminal groups. Most studies has involved their physical properties and polymer composition, while attention has rarely been paid to their emulsification in an oil-water system. Herein we synthesized a cyclic polymer with polystyrene side chains via ring-expansion metathesis polymerization and click-chemistry. This cyclic polymer was compared with linear polystyrene in order to investigate the effect of cyclic topology on preparing porous particles by emulsion templating methods. The contribution of cyclic topology to emulsification originates from the formation of hollow microspheres with the use of cyclic polymer while linear polymer only afforded solid microspheres. With addition of hexadecane as soft template, both cyclic polymer and linear polymer emulsions were successfully converted into porous particles. Superior to linear polymer, cyclic polymer enables the stabilization of emulsion droplets and the tuning of porous morphology. It is revealed that cyclic polymer with nanoring shape tends to assemble at the interfacial area, leading to the Pickering effect that decelerates the macrophase separation. Furthermore, the unique porous feature of polymer particles affords a convenient application for the detection of trace explosive.

Gelatin intervened synthesis of calcite cocoon-like microparticles assembled with small rhombohedra at low temperature

Biomimetic crystallisation of calcium carbonate (CaCO3) in the presence of gelatin was investigated at room temperature (RT) and at low temperature. The presence of gelatin was found to alter the normal crystallisation of large calcite rhombohedral crystals, leading to the unique morphosynthesis of calcite microcrystals. Compared to the overgrowth of irregular calcite products synthesised in the presence of gelatin at RT, predominant cocoon-like and minor rosette-like microparticles with the typical size of 2–4 μm were obtained at low temperature (4°C). The samples showed that the cocoon-like microparticles were orderly stacked by small well faceted rhombohedra. The formation of hollow microspheres was confirmed by observing the consumption of the internal precursors, further indicative of the unique low temperature modulating effects of gelatin. The present biomimetic approach is simple and biosafe, and the obtained cocoon-like hollow microparticles could be potentially used for biomedical purposes.

Experience in plasma production of hollow ceramic microspheres with required wall thickness

With the example of zirconium dioxide, a process for the plasma production of hollow spherical powders with controllable shell thickness has been studied. The formation of hollow microspheres, or microballoons, is achieved through melting of an initial porous powder in the plasma jet of a DC plasma gun. Hollow microballoons 40 to 125μm in size with shell thickness 2μm and over were obtained. The experience in measuring the characteristics of hollow microspheres, namely their sizes, density, and wall thickness, is outlined. A procedure for preliminary and final classification of powders which enables the production of spheres with desired volumetric density and wall thickness is proposed.

Reactable ionic liquid-assisted rapid synthesis of BiOI hollow microspheres at room temperature with enhanced photocatalytic activity

BiOI hollow microspheres have been rapidly synthesized through a facile reactable ionic liquid 1-butyl-3-methylimidazolium iodine ([Bmim]I)-assisted microemulsion method at room temperature. The formation mechanism of the BiOI hollow microspheres has been investigated. The BiOI hollow microspheres were formed through self-assembly and inside-out Ostwald ripening growth mechanism. During the reactive process, the ionic liquid, which acts as the solvent, reactant and template at the same time, plays a crucial role on the formation of hollow microspheres. In addition, the influencing factors (such as the reactant, the concentration of ionic liquids and the amount of acetic acid) of the formation of BiOI hollow microsphere have also been explored. The photocatalytic ability of the as-prepared photocatalysts was evaluated using rhodamine B (RhB) as a target pollutant. After systematic characterizations, the relationship between the structure of the photocatalyst and the photocatalytic activities were also discussed in detail. It can be assumed that the enhancing photocatalytic activity of BiOI hollow microspheres could be attributed to the improved light harvesting, shortened diffusion pathways, high BET surface area and faster interfacial charge separation. O2˙− and h+ were the main active species for the photocatalytic degradation of RhB. It is hoped that this rapidly synthetic route at room temperature can be extended to the purposive preparation of other hollow microsphere materials.

Preparation of a novel rape pollen shell microencapsulation and its use for protein adsorption and pH-controlled release

This study aims to synthesize hollow microspheres (HMS) from rape pollen via H3PO4 hydrothermal carbonization. The rape pollen hollow shell was used as the carrier and bovine serum albumin as a model protein. The properties of HMS were characterized by scanning electron microscope (SEM), solid-state nuclear magnetic resonance and elemental analysis. The SEM images clearly showed that the HMS had perfect spherical morphology and porous hollow surface. In the separated filtrate, a large number of sucroses were detected by high-performance liquid chromatography, suggesting that the hydrolysis of starch molecules occurred during the hydrothermal process. The formation of HMS was that the rape pollen inclusion was removed from rape pollen shell to preserve integral HMS by H3PO4 hydrothermal. The HMS possessed amphiphilic surfaces, which was suitable for protein adsorpion and pH-controlled release application.

Solvothermal Synthesis of Bi2WO6 Hollow Microspheres Via Ostwald Ripening with Their Enhanced Photocatalytic Activity

Bi2WO6 hollow microspheres were successfully synthesized by solvothermal process in the presence of urea at proper ethylene glycol (EG)/absolute ethanol (AE) volume ratio (1:1). The samples consisted of microspheres with an average diameter of 1 μm, and the shell consisted of numerous nanoplates. The effect of solvent, the ratio of EG/AE solvents and urea amount on the morphology of the samples was studied systematically, indicating that a certain ratio of EG/AE and urea amount played an important role in the formation of hollow microspheres. Based on the detailed investigation, the formation mechanism of the hollow interior by EG-induced Ostwald ripening process was proposed. By contrast, the Bi2WO6 hollow microspheres exhibited higher catalytic activity for degradation of Rhodamine B under xenon lamp irradiation, and nearly 100 % Rhodamine B is degraded within 120 min.

Self-construction of Magnetic Hollow La0.7Sr0.3MnO3 Microspheres with Complex Units

Perovskite structure La0.7Sr0.3MnO3 magnetic hollow microspheres with complex units were prepared via the hydrothermal route without hard and soft templates. The formation of hollow microspheres follows the self-construction mechanism involving oriented attachment, dissolution, and recrystallization processes. It exhibits a ferromagnetic behavior at room temperature.

Room temperature preparation of cuprous oxide hollow microspheres by a facile wet-chemical approach

Cuprous oxide hollow spheres have potential applications in drug-delivery carriers, biomedical diagnosis agents, and cell imaging. From a commercial point of view, the low-temperature, template-free, facile method is widely popular synthetic method for the synthesis of cuprous oxide hollow spheres. In this letter, we describe a novel facile template-free wet-chemical route to prepare crystallized cuprous oxide microspheres at room temperature. XRD patterns and SEM images revealed that pure crystallized cuprous oxide hollow microspheres were successfully obtained at room temperature. The diameter of cuprous oxide hollow sphere can be adjusted (0.7–7 μm) by concentration control of hydrazine hydrate. Generated N 2 gas bubbles in the aqueous solution, serving as “soft” templates, play a key role in the formation of hollow microspheres.

A Fast and Template Free Synthesis of Tb:Y2O3 Hollow Microspheres Via Supercritical Solvothermal Method

The design of template-free hollow microspheres in a very short period of time will be of great importance to save energy and time and allow rapid production. We succeeded in the rapid synthesis of precursor material via a supercritical solvothermal method followed by subsequent heating to obtain Tb:Y2O3 hollow microspheres. The prepared precursor material was actually composed of Y(OH)3 and Y(OH)CO3 phases. The hollow microspheres seemed to be formed through the aggregation of nanoparticles under supercritical conditions. The formation mechanism of hollow microspheres in the present synthesis is the Ostwald ripening process. Effects of reaction temperature and pH of the starting solution were investigated to understand the effect on the formation of hollow microspheres. Well-shaped Tb:Y2O3 hollow microspheres showed strong green emission at 540 nm under 304 nm light excitation. The effect of doping concentrations and calcinations temperature was investigated.

Synthesis and characterization of uniform‐sized hollow chitosan microspheres

AbstractHollow chitosan (CS) microspheres were obtained using an inverse‐emulsion crosslinking method. The temperature and viscosity of the CS emulsion affected the characteristics of the derived microspheres. The microspheres were characterized by differential scanning calorimetry, Fourier transform infrared (FT‐IR) spectroscopy, transmission electron microscopy, optical microscopy, scanning electron microscopy (SEM), and laser particle size analysis. FT‐IR indicated the sequence of transformations taking place before, during, and after the crosslinking of CS. Optical microscopy and SEM confirmed the spherical morphology of the gel. The formation of hollow microspheres with a single cavity was identified by SEM. The CS microspheres exhibited a narrow particle size distribution. Furthermore, particle size could be controlled by changing the stirring speed. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:40–47, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20145

Template-directed synthesis of MS (M=Cd, Zn) hollow microsphere via hydrothermal method

CdS, ZnS hollow microspheres were prepared with chitosan as the synthesis template at 140 and 150 °C, respectively, by hydrothermal method. The resultant products were characterized by X-ray diffraction (XRD) measurements in order to determine the crystalline phase of the products. The structural and morphological features of the nanoparticles were investigated by transmission electron microscopy (TEM) and ultraviolet–visible diffuse reflection spectroscopy (DRS). The experimental results indicated that all the nanoparticles aggregated into hollow microspheres and chitosan as a template played an important role in the formation of hollow microspheres. In addition, an intermediate complex structure-controlling possible reaction mechanism was proposed in this paper.

Preparation of dendrimer-like copolymers based on polystyrene and poly(l-lactide) and formation of hollow microspheres

The three generations dendrimer-like copolymers C(PSt(PLLA(PSt–PNAS)2)2)3 and C(PSt(PLLA(PSt–PNAS)2)2)4 have been successfully synthesized by combination of ATRP and ROP. Diethanol amine and 2,2-bis(methylene-2-bromoisobutyrate) propionyl chloride (BMBIBPC) were used as divergent reagents, respectively, before preparations of the second and the third generations. The resultant polymers were characterized by GPC and 1H NMR. Then the outermost PSt–PNAS in the dendrimer-like copolymers was cross-linked via substitution reaction of NAS with ethylene diamine, and at the same time, the PLLA segments in the second generation were decomposed in dilute THF or CHCl3 solution, forming hollow particles. The resultant morphologies were characterized by SEM and DLS methods, and spherical particles with various sizes were observed. The hollow particles may have potential applications in catalysis and bioengineering.

Magnesium Aluminate (MgAl2O4) Spinel Powders from Water‐Based Sols

Magnesium aluminate (MgAl2O4) spinel powders of irregular and spherical morphologies were obtained from the bi‐component water‐based sols following the sol–gel and sol–emulsion–gel methods, respectively. For the synthesis of the oxide microspheres, the surfactant concentration and viscosity of the sols were found to affect the characteristics of the derived microspheres. The gel and calcined powders were investigated by using thermogravimetry analysis, differential thermal analysis, X‐ray diffraction (XRD), optical and scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy, and particle size analysis. XRD results indicated crystallization of the only phase MgAl2O4 spinel from 200° to 1000°C. Formation of hollow microspheres with a single cavity was identified by SEM.

POE/PLGA composite microspheres: formation and in vitro behavior of double walled microspheres

The poly(ortho ester) (POE) and poly(d,l-lactide-co-glycolide) 50:50 (PLGA) composite microspheres were fabricated by a water-in-oil-in-water (w/o/w) double emulsion process. The morphology of the composite microspheres varied depending on POE content. When the POE content was 50, 60 or 70% in weight, the double walled microspheres with a dense core of POE and a porous shell of PLGA were formed. The formation of the double walled POE/PLGA microspheres was analysed. Their in vitro degradation behavior was characterized by scanning electron microscopy, gel permeation chromatography, Fourier-transform infrared microscopy and nuclear magnetic resonance spectroscopy (NMR). It was found that compared to the neat POE or PLGA microspheres, distinct degradation mechanism was achieved in the double walled POE/PLGA microspheres system. The degradation of the POE core was accelerated due to the acidic microenvironment produced by the hydrolysis of the outer PLGA layer. The formation of hollow microspheres became pronounced after the first week in vitro. 1H NMR spectra showed that the POE core was completely degraded after 4 weeks. On the other hand, the outer PLGA layer experienced slightly retarded degradation after the POE core disappeared. PLGA in the double walled microspheres kept more than 32% of its initial molecular weight over a period of 7 weeks.

Emulsion–ion extraction technique for synthesis of hollow bicomponent oxide microspheres

H ollow ox ide microspheres in the bicomponent systems Al2O3-28 wt-%SiO2 (AS) ( mullite) , Al2O3- 13 wt-%T iO2 (AT) , and Z rO2-10 wt-%Y2O3 ( Z Y) were prepared by the emulsion-ion extraction technique. Monodisperse microsphere formation was found to depend on the experimental parameters adopted during ion ex traction and the surfactant concentration present in the emulsion system. Powder characteristics were investigated using X-ray diffraction, optical and scanning electron microscopy, and particle size analysis. The gel microspheres in the AS, AT , and ZY systems started crystallising at about 900, 800, and 400 °C respectively. The oxide microspheres were mostly spherical in morphology and the sphericity was retained even after calcination at 1300 °C for 1 h. Formation of hollow microspheres with a single spherical cavity was identified by SEM . All oxide microspheres calcined at 1300 °C for 1 h ex hibited a particle size distribution within the range 5-60 μm, the average size ( d50) varying from 19 to 22 μm. BCT / 537

Sol-emulsion-gel synthesis of hollow mullite microspheres

Hollow mullite microspheres were obtained from emulsified diphasic sols by an ion extraction method. The surfactant concentration and viscosity of the sols were found to affect the characteristics of the derived microspheres. The gel and calcined microspheres were investigated by using thermogravimetry analysis (TGA), differential thermal analysis (DTA), Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), optical and scanning electron microscopy (SEM) and particle size analysis. TGA indicated the removal of most of the volatiles, i.e. 30.77 wt% up to about 500°C. Crystallization of the Si-Al spinel at 900°–970°C in gel microspheres was confirmed by DTA and XRD. XRD results also showed the formation of orthorhombic mullite at 1200°C. FTIR indicated the sequence of transformations taking place during heat-treatment of gel microspheres at different temperatures. The optical and scanning electron microscopy confirmed the spherical morphology of the gel and calcined particles. Formation of hollow microspheres with a single cavity was identified by SEM. The particle size distribution of the mullite microspheres calcined at 1300°C/1h exhibited a size range of 6–100 μm with an average particle size (d50) of 22.5 μm.

Regularities of the formation of polystyrene hollow microspheres

The effect of different factors on the formation of hollow microspheres in the process of foaming of suspended polystyrene granules has been investigated at temperatures close to the boiling point of the foaming agent. It is shown that the non-isothermal kinetics of foaming are identical in character to the thermomechanical curves, and critical sizes of initial particles, at which a polycellular structure is formed, have been determined. It was found that these critical particle sizes depend on the diffusion coefficient of the foaming agent, and that as a rule a higher diffusion rate leads to an increase in the critical size of granules, and to increased probability of the formation of monospheres. The data obtained are analysed mathematically, and a set of equations is derived where by kinetic regularities of the foaming of polystyrene granules by liquid foaming agents are described.