Hollow Spherical Particles Research Articles

A Continuum Damage Mechanics Model for the Static and Cyclic Fatigue of Cellular Composites.

The fatigue behavior of a cellular composite with an epoxy matrix and glass foam granules is analyzed and modeled by means of continuum damage mechanics. The investigated cellular composite is a particular type of composite foam, and is very similar to syntactic foams. In contrast to conventional syntactic foams constituted by hollow spherical particles (balloons), cellular glass, mineral, or metal place holders are combined with the matrix material (metal or polymer) in the case of cellular composites. A microstructural investigation of the damage behavior is performed using scanning electron microscopy. For the modeling of the fatigue behavior, the damage is separated into pure static and pure cyclic damage and described in terms of the stiffness loss of the material using damage models for cyclic and creep damage. Both models incorporate nonlinear accumulation and interaction of damage. A cycle jumping procedure is developed, which allows for a fast and accurate calculation of the damage evolution for constant load frequencies. The damage model is applied to examine the mean stress effect for cyclic fatigue and to investigate the frequency effect and the influence of the signal form in the case of static and cyclic damage interaction. The calculated lifetimes are in very good agreement with experimental results.

Synthesis and photocatalytic performance of hollow sphere particles of SiO2-TiO2 composite of mesocellular foam walls

Abstract Hollow Microspheres of SiO 2 -TiO 2 photocatalysts whose walls are made up of mesoporous cellular foams were synthesized with the aid of hexane as a swelling agent and P123 as a pore template by an emulsion templating method. Pore structure of materials and crystal phase of titanium oxide was tailored by hydrothermal and calcination temperature during synthesis of samples. The samples were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), N 2 adsorption–desorption experiments, X-ray photoelectron spectroscopy (XPS) and X ray diffraction (XRD) techniques. The effect of pore structure and titania phase on photoactivity were evaluated by methylene blue (MB) degradation test under UV light as well. Results showed that hydrothermal temperature during synthesis process has a significant effect on pore and window sizes of mesostructured cellular foam. Interestingly, for the sample hydrothermally treated at higher temperature (130 °C), anatase to rutile transformation was avoided after calcination treatment as high as 800 °C. The highest photocatalytic activity was detected from the sample hydrothermally treated at 130 °C and calcined at 800 °C for which the highest degree of crystallinity and anatase phase as well as enhanced pore connectivity was obtained.

Size control of CH3NH3PbBr3 perovskite cuboid fine crystals synthesized by ligand-free reprecipitation method

Cuboid fine crystals of methylammonium lead tribromide (MAPbBr3) perovskite have been synthesized by ligand-free reprecipitation method employing N,N-dimethylformamide (DMF) and 1,2,4-trichlorobenzene (TCB) as good and poor solvents, respectively. A small amount of DMF solution dissolving precursor chemicals of MAPbBr3 was rapidly injected to TCB under vigorous stirring to promote the reprecipitation. Mean crystal size could be varied between 70 and 600 nm by controlled addition of cyclohexane to TCB, since cyclohexane has been found to play a role to retard droplet diffusion. Cyclohexane was miscible with TCB but poorly miscible with DMF. Thus, addition of cyclohexane to TCB retarded diffusion of the injected droplets of DMF solution for reprecipitation of MAPbBr3. As the mixing of good and poor solvents was retarded, the recrystallization process was also slowed down, resulted in a small number of nuclei and their growth to large size. Moreover, extreme addition of cyclohexane has resulted in a hollow core spherical particles of MAPbBr3 due to aggregation of the cuboid fine crystals at the boundary between the added droplet and the poor solvent, so that the spheres formed preserving the shape of the droplet. Due to the limited miscibility of cyclohexane to DMF, increasing the cyclohexane content resulted in reduced rate of diffusion of the injected MAPbBr3 solution, thus increasing the size of the crystals.

Water Absorption Behavior of Polystyrene Particles Prepared by Emulsion Polymerization with Nonionic Emulsifiers and Innovative Easy Synthesis of Hollow Particles.

Submicrometer-sized raspberry-like polystyrene (PS) particles, which were prepared by emulsion polymerization with polyoxyethylene nonylphenyl ether nonionic emulsifier (Emulgen 910, HLB 12.2) and potassium persulfate initiator, contained 8.5 vol % (relative to the particle) of water and 5.5 wt % (relative to PS) of Emulgen 910 in the inside. The water absorption decreased the glass transition temperature of the PS particles dispersed in an aqueous medium. The wt % (relative to PS) of the incorporated Emulgen 910 increased with increasing initial Emulgen 910 concentration in the emulsion polymerization, but the wt % (relative to the total Emulgen 910 used) of the incorporated Emulgen 910 was constant at approximately 50% independent of the initial concentration. The vol % (relative to particle) of water increased to 46% by heat treatment at 90 °C for 24 h, which was based on further water absorption, and resulted in spherical hollow particles, where the amount of the incorporated Emulgen 910 remarkably decreased in a short treatment and then remained almost constant during the heat treatment. After another 24 h treatment, the percentage of nonhollow particles increased gradually, which was based on the escape of the water domain together with Emulgen 910 from the inside of the particles. On the other hand, spherical PS particles prepared by emulsifier-free emulsion polymerization did not contain water in the inside and were not changed to hollow ones by a similar heat treatment. From these results, an innovative easy method to synthesize hydrophobic hollow PS particles is proposed.

Optimally designed interface of lithium rich layered oxides for lithium ion battery

Abstract Particle morphology structure design combined with surface modification has been applied to improve the electrochemical properties of lithium rich layered oxides. Hollow spherical lithium rich layered Li1.2Mn0.54Ni0.13Co0.13O2 oxides with different shell thickness are synthesized by co-precipitation followed by calcination. The morphology and interior structure have been investigated by SEM and cross section, and their electrochemical properties have been evaluated to identify an appropriate shell thickness. Furthermore, a Zr compound coating layer has been applied to modify the interface between corrosive electrolyte and hollow spherical particles with an appropriate shell thickness. The Electrochemical impedance spectroscopy shows hollow spherical structure and Zr compound coating layer both can modificate the electronic and ionic transmission capacities and inhibit their deterioration during charge-discharge process at the same time. The HRTEM tests indicate that hollow spherical structure and Zr compound coating layer can dramatically suppress Mn dissolution in electrolyte and make the crystal structure more stable during the electrode process. Therefore, a surface modification combine with the hollow spherical structure (with an appropriate shell thickness) can effectively enhance these electrochemical properties of lithium ion layered oxides.

Preparation of Flattened Cross-Linked Hollow Particles by Suspension Polymerization in a Solid Dispersion Medium.

Flattened cross-linked hollow poly(divinylbenzene) (PDVB) particles with encapsulated n-hexadecane (HD) were successfully prepared through suspension polymerization using the self-assembling of phase-separated polymer (SaPSeP) method, in which the solid dispersion medium was gelled by gellan gum and compressed. The solid phase induced by gellan gum can be easily changed to a liquid state by heating, allowing the obtained particles to be easily recovered after polymerization. When the polymerization was conducted in the solid dispersion medium without compression, spherical hollow PDVB/HD composite particles were obtained. In contrast, when the polymerization was conducted with the compression of the solid dispersion medium, flattened hollow PDVB/HD composite particles were obtained. The shape of the flattened hollow polymer particles was controlled by changing the compression ratio of the solid phase, and the size could also be controlled by changing the DVB/HD droplet size using the Shirasu porous glass membrane-emulsification technique. Furthermore, flattened hollow particles larger than 20 μm in size were obtained, but it was difficult to obtain spherical hollow particles of such large size using the SaPSeP method.

Beta-Glucan Particles as Vaccine Adjuvant Carriers.

Glucan particles (GPs) are spherical hollow particles derived from Saccharomyces cerevisiae cell walls and mainly consist of β-1, 3-D-glucans. The inner hollow cavity of glucan particles can be loaded with different compounds, including protein antigens, and delivered to macrophages and dendritic cells. Moreover, the GP delivery system possesses β-glucan's intrinsic immunostimulatory properties. Therefore, GPs serve as both an antigen-presenting cell-targeted delivery system and an adjuvant.Here, we describe the production of GPs from S. cerevisiae using hot alkaline and solvent extraction and characterization of these particles for morphology, particle density, and hydrodynamic volume. A detailed protocol for loading and entrapping a model antigen, ovalbumin (OVA), into these particles using yeast RNA is presented. Similar methods are used to load pathogen-specific antigens (peptides, proteins, soluble extracts) which then can be tested in in vivo vaccination models.

Hollow spheres as nanocomposite fillers for aerospace and automotive composite materials applications

Abstract There were studied four types of powder filler materials for polyolefin composite parts production for automotive and aerospace industry. There was confirmed, that the particle shape has a strong effect on the acoustic and mechanical properties of the powder bed as influenced by the varying packing density. The calcium carbonate spherical hollow particles exhibited the best aerodynamic performance when aerated and were completely fluidised. Simultaneously they were exhibiting the easy flowing behaviour as reflected in the observed flowability of 4.71. In contrary to this, the flat lamellar geometry of the precipitated calcium carbonate resulted in the worst fluidisation behaviour, as the aeration energy was 2.5× higher in comparison to the spherical particles. Remaining samples under study, i.e. flash calcined kaolin and dolomite powder, exhibited cohesive rheological behaviour as reflected in the observed flowability. There was found a clear correlation between powder rheological and electrostatic charge data with the observed acoustic performance as reflected in the frequency dependence of the normal incident sound damping coefficient. This was demonstrated by a relatively high increase in the damping efficiency with increasing porosity of the powder bed as reflected in the decreasing packing density. However the best fit was found between the absolute value of the electrostatic charge values and the sound damping properties.

DETERMINING THE ROLE OF INDIVIDUAL FLY ASH PARTICLES IN INFLUENCING THE VARIATION IN THE OVERALL PHYSICAL, MORPHOLOGICAL, AND CHEMICAL PROPERTIES OF FLY ASH

The properties of fly ashes vary because of the differences in the properties of their individual particles, and the determination of variation in these properties is of interest to the industries which use pulverized raw fly ash in applications, such as in cementitious materials and in the recovery of certain rare elements from raw fly ash. To investigate the differences in individual particles, four pulverized raw fly ashes from thermal power plants of the Czech Republic were used in this research. It was observed from FE-SEM that all four fly ashes consist of glassy hollow spherical, solid spherical, porous spherical, bright spherical, porous slaggy and compact slaggy particles. Box and whisker diagrams were plotted from the data of EDX individual particle analyses, which showed that the data of percentages for the Si, Al, and Fe elements is more scattered as compared to other elements. It was further observed from ternary phase diagrams and pseudo coloured images, that nature of fly ash particles changes from alumino silicate glassy to alumino silicate calcite metallic to pure ferro-metallic,where glassy particles showed high percentages and pure calcite particles were absent in fly ashes. Furthermore, a comparison between the XRF, the EDX total area analyses, showed that the EDX individual particle analysis gives more realistic and reliable data with median, mean, and the standard deviation for percentages of each element present in the fly ashes.

Micro porous carbon spheres from cyclodextrin nanosponges

A series of carbons were prepared by pyrolysis of hyper cross-linked cyclodextrins, also known as nanosponges (NS). Pore structure analysis showed that pores with a range size of 5–16 A can be created from β-CD an NS cross-linked with pyromellitic dianhydride (PY). NS cross-linked with hexamethylene diisocyanate (HD) was ineffective to produce pores. SEM observation reveals a peculiar morphology of the PY-NS carbon, made of perfectly spherical hollow particles. TGA and FT-IR studies demonstrate that the PY-NS is the more efficient carbon precursor.

Dynamic Effects in Elastothermodynamic Damping of Hollow Particle Reinforced Metal-Matrix Composites

The Metal-Matrix Composites (MMCs) containing hollow spherical reinforcements are under active development for the applications such as space structures, submarine hulls etc. where weight is of critical importance. When these materials are subjected to a time varying strain field, energy is dissipated because of the thermoelastic effect (Elastothermodynamic Damping or ETD). The quasi-static ETD analysis for the MMCs containing hollow spherical particles has been reported in literature. The entropic approach, which is better suited for composite materials with perfect or imperfect interfaces, is used for the analysis. In the present work, the effect of inertia forces is carried out on ETD of hollow particle-reinforced MMCs. For given particle volume fractions (Vp), the inertia forces are found to be more significant at higher value of thermal parameter (ΩT1) (alternatively, frequency of vibration if reinforcement radius is fixed), large cavity volume fraction (Vh) and low value of the parameter B1.

Micelles driven magnetite (Fe3O4) hollow spheres and a study on AC magnetic properties for hyperthermia application

Here we have discussed about designing the magnetic particles for hyperthermia therapy and done some studies in this direction. We have used oleylamine micelles as template to synthesize hollow–nanospheres (HNS) of magnetite by solvo-thermal technique. We have shown that oleylamine plays an important role to generate hollow particles. Structural analysis was done by XRD measurement and morphological measurements like SEM and TEM was performed to confirm the shape and size of hollow sphere particles. The detail magnetic measurements give an idea about the application of these HNS for magnetic heating in hyperthermia therapy. In vitro cytotoxicity studies reveal that tolerable dose rate for these particles can be significantly high and particles are non-toxic in nature. Being hollow in structure and magnetic in nature such materials will also be useful in other application fields like in drug delivery, drug release, arsenic and heavy metal removal by adsorption technique, magnetic separation etc.

Effect of an inhomogeneous interphase zone on the bulk modulus of a particulate composite containing spherical inclusions

The effects of an inhomogeneous interphase zone on the effective bulk modulus of particulate composites containing large concentrations of inclusions are analyzed. The composite is modeled as a suspension of elastic homogeneous hollow spherical particles in a continuous elastic matrix. An interphase zone surrounding inclusions where the matrix material has elastic moduli with radial variation that asymptotically assume a constant value far away from particles is then modeled. The related elastic problem of a single inclusion in a finite matrix subjected to a spherically symmetric load is considered and a closed-form solution in terms of hypergeometric functions is determined. This analytical solution is then employed to derive an explicit expression for the effective bulk modulus. A detailed parametric analysis is finally performed to investigate the influence of the geometric characteristics and elastic properties of the graded interphase zone for composites containing voids or solid/hollow inclusions.

Recovery potentials of cenospheres from bituminous coal fly ashes

Cenospheres are defined as hollow spherical particles with density less than water. This definition is based on natural concentration of cenospheres from fly ashes in wet disposal sites, i.e. ponds or lagoons. On the other hand, the lowest-density oxide in fly ashes, crystalline silica, has a density of 2.6g/cm3. Therefore, hollow particles with densities of up to 2.6g/cm3 are also present in fly ashes depending on the wall thickness and the ratio of the hollow part. These heavier cenospheres could also have high-value applications in construction industry as fillers and reinforcements. In this study, recovery potentials of cenospheres from two bituminous coal fly ashes were examined as a function of density and size. Fly ash samples from Çatalağzı (CFA) and Sugözü (SFA) thermal power plants were first subjected to float–sink, wet sieving and air classification tests to separate them into various products. These products were then analyzed under optical microscope for their cenosphere contents on the basis of point counting and area estimations. Separation efficiency was evaluated in terms of yield, cenosphere content and recovery of the products. Overall results showed that CFA has much more cenospheres than SFA, and cenosphere contents decreased with decreasing size and increasing density for both samples. Despite similar variations in cenosphere contents through density and size, CFA exhibited much higher yields and recoveries compared to SFA for the respective product.

Spray Solution Combustion Synthesis of Metallic Hollow Microspheres

A spray solution combustion synthesis method has been developed to produce hollow spherical metal nanostructured particles. In this approach, combustion reactions in the liquid solution contribute 100% of the overall energy released during the synthesis process without the involvement of an external gaseous flame. It has been shown that this method is effective for the synthesis of spherical hollow particles of metals (Ni, Cu) with an average diameter of about 3 μm and wall thicknesses of about 20 nm.

Ion-shaping of embedded gold hollow nanoshells into vertically aligned prolate morphologies.

Ion beam shaping is a novel technique with which one can shape nano-structures that are embedded in a matrix, while simultaneously imposing their orientation in space. In this work, we demonstrate that the ion-shaping technique can be implemented successfully to engineer the morphology of hollow metallic spherical particles embedded within a silica matrix. The outer diameter of these particles ranges between 20 and 60 nm and their shell thickness between 3 and 14 nm. Samples have been irradiated with 74 MeV Kr ions at room temperature and for increasing fluences up to 3.8 × 1014 cm−2. In parallel, the experimental results have been theoretically simulated by using a three-dimensional code based on the thermal-spike model. These calculations show that the particles undergo a partial melting during the ion impact, and that the amount of molten phase is maximal when the impact is off-center, hitting only one hemisphere of the hollow nano-particle. We suggest a deformation scenario which differs from the one that is generally proposed for solid nano-particles. Finally, these functional materials can be seen as building blocks for the fabrication of nanodevices with really three-dimensional architecture.

Bubble-filled silica microfibers from multiphasic flows for lightweight composite fabrication

Hollow spherical shells made of various oxides have long been used as filler materials to prepare light-weight materials with high specific strength. We present the fabrication of bubble-filled silica microfibers with controlled size and structure by using multiphase flow in a coaxial glass capillary device. The multiphase flow is controlled to generate a jetting gas-in-water-in-oil core–sheath stream, which is converted to flexible nanoparticle–polymer composite fibers filled with bubbles. The production rate of these bubble fibers can reach up to 2000cm/min. These flexible fibers can be manipulated to desired shapes or architectures and subsequently be sintered via thermal treatment. We demonstrate the fabrication of bubble fiber-filled light weight composite, which potentially has a significant advantage over conventional light-weight composites made with spherical hollow particles.

Millimeter‐size polyethylene hollow spheres synthesized with MgCl2‐supportedZiegler‐Natta catalyst

ABSTRACTPolyethylene hollow spheres with diameters of 0.4–2 mm were synthesized by a two‐step slurry polymerization in a single reactor with a spherical MgCl2‐supported Ziegler‐Natta catalyst activated by triethylaluminum, in which the first step was prepolymerization with 0.1 MPa propylene and the second step was ethylene polymerization under 0.6 MPa. The prepolymerization step was found necessary for the formation of hollow spherical particles with regular shape (perfectly spherical shape). The effects of adding small amount of propylene (propylene/ethylene < 0.1 mol/mol) in the reactor after the prepolymerization step were investigated. Average size of the polymer particles was increased, and the polymerization rate was markedly enhanced by the added propylene. Development of the particle morphology with polymerization time was also studied. The polymer particles formed by less than 20 min of ethylene polymerization showed hollow spherical morphology with thin shell layer. Most of the particles had ratio of shell thickness/particle radius smaller than 0.5. By prolonging the ethylene polymerization, the shell thickness/particle radius ratio gradually approached 1, and the central void tended to disappear. Central void in polymer particles formed from smaller catalyst particles disappeared after shorter time of polymerization than those formed from bigger catalyst particles. The shell layer of the hollow particles contained large number of macro‐, meso‐ and micro‐pores. The mesopore size distributions of four typical samples were analyzed by nitrogen adsorption–desorption experiments. A simplified multigrain model was proposed to explain the morphogenesis of the hollow spherical particles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2016,133, 43207.

Effect of a micro-copolymer addition on the thermal conductivity of fly ash mortars.

In this study, a copolymer composed of hollow spherical particles with an average particle size of 90 µm was evaluated as a lightweight aggregate in Portland cement-fly ash mortars to improve the thermal conductivity (k) of the composite. Mortars were produced for three different water/binder ratios by mass (w/b), 0.4, 0.5 and 0.6. Optimized proportions were obtained for a minimum target compressive strength of 35 kgf/cm2 (3.4 MPa) according to the requirements of Mexican standards for non-structural masonry units. Thermal conductivity was determined for dry and saturated samples through the transient plane technique with average results of 0.16 W/(m·K) and 0.31 W/(m·K), respectively. These values represent an increment of 23 % and a reduction of 33 %, respectively, in comparison to an efficient Portland cement-based commercially available thermal insulator.

Thermal response of a PVCL–HA conjugate

ABSTRACTThe synthesis and self‐assembling of a thermoresponsive conjugate of hyaluronic acid (HA) and poly(N‐vinylcaprolactam) (PVCL) is reported. Both polymers were end functionalized: HA via reductive amination, thereby introducing an azide endgroup to the chain end, and PVCL via thioetherification to introduce a propargyl group. The two were coupled with a copper assisted “click” reaction into a bioconjugate composed of HA blocks with the molar mass 3,600 g mol−1 (1618 saccharide units) and PVCL blocks of 3,500 g mol−1 (∼25 repeating units). The cloud point temperature measured by transmittance was 50–51 °C in water. The calorimetrically observed phase transition temperature of PVCL in the conjugate increased by 2 °C to 47.7 °C, whereas the enthalpy of the phase transition was unaffected by the conjugation. HA‐PVCL conjugate self‐assembles in water upon heating into monodisperse, colloidally stable, hollow spherical particles whose size may be tuned with the heating rate of the solution. Slow and fast heating resulted in vesicles with the hydrodynamic radii of 443 or 275 nm, respectively. The heating rate did not, however, affect the cloud point. Salt did not noticeably affect the size of the polymer particles, presumably because of interactions between the HA and PVCL blocks. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 425–436