Core Shell Hybrid Microspheres Research Articles

Fabrication of high-temperature-resistant bondline based on multilayer core–shell hybrid microspheres for power devices

This paper presents a fabrication method for high-temperature-resistant bondlines based on Cu@Ag@Sn multilayer core–shell hybrid microspheres in which a Ag layer was adopted to accelerate the consumption of a Sn layer. The phase transformation and microstructural evolution during the bonding process were investigated in detail. After the microspheres were heated at 250 °C for 20 min under a pressure of 0.5 MPa, the bondline could withstand high operation temperatures of up to 480 °C. After reflowing at 250 °C for just 5 min, the outer low-melting-point Sn layer was completely consumed. After 20 min, the bondline was composed of Ag3Sn and Cu3Sn intermetallic compounds with a dispersion of Cu microspheres. The average shear strengths of the resulting bondlines were 39.9 and 31.9 MPa at room temperature and at 400 °C, respectively.

Silica/Chitosan Core–Shell Hybrid-Microsphere-Supported Pd Catalyst for Hydrogenation of Cyclohexene Reaction

This paper presents a simple microfluidic method to prepare monodispersed palladium nanoparticles supported on silica/chitosan core–shell hybrid microspheres. Because a large amount of −NH2 provided by chitosan has a strong force with metal ions, Pd nanoparticles loaded on the microspheres kept monodispersed and had a mean diameter of only 2–3 nm. In addition, the core–shell structure indicating that the chitosan was mainly distributed on the shell of the microspheres results in that palladium is mainly loaded on the shell too, which can effectively reduce mass transfer distance between reactant and catalyst. Therefore, the supported Pd catalyst showed a superb catalytic performance through the hydrogenation of cyclohexene. Furthermore, silica/chitosan-supported catalyst can be reused many times without an obvious loss of its activity, and it will have promising application in other similar hydrogenation reactions.

Synthesis and characterization of porous surface molecularly imprinted silica microsphere for selective extraction of ascorbic acid

Molecularly imprinted polymers (MIPs) with core-shell structure for efficient, reliable, and selective extraction of ascorbic acid (AA) were developed via co-polymerization process based on acrylamide (AM) as a functional monomer, ethylene glycol dimethacrylate (EGDMA) as cross-linker, 2,2'-azobis(2-methylpropionitrile) (AIBN) as initiator, and AA as template. The inorganic core comprised of amino-functionalized silica microspheres (AFSM) was prepared by co-condensation of tetraethylorthosilicate (TEOS) and (3-aminopropyl)trimethoxysilane) (APTMS) in a water-in-oil (W/O) macroemulsion. The synthesized materials were characterized by IR-ATR, SEM, and N2 adsorption–desorption isotherm. The binding properties and selectivity of the AFSM@MIP and AFSM@NIP (i.e., non-imprinted polymers) were demonstrated by adsorption capacity and imprinting factor obtained based on UV–Vis absorption measurements. Furthermore, synthesis conditions were optimized such that imprinting efficiency and adsorption capacity were maximized. Finally, it was demonstrated that generated MIP core-shell hybrid microspheres provide rapid adsorption with high binding capacities (up to 5.08 mg g−1), excellent imprint factors, and exceptional reusability. A comparative study using AFSM@MIP and AFSM@NIP for simultaneous extraction of AA and citric acid (CA), allowed verifying the excellent selectivity of AFSM@MIP, which presented an imprinting factor of 2.30.

Molecularly imprinted core–shell hybrid microspheres for the selective extraction of vanillin

Molecularly imprinted polymers (MIPs) with a core–shell structure for efficient, reliable, and selective extraction of vanillin via solid-phase extraction (SPE) and incubation methods were developed using a sol–gel process based on (3-aminopropyl)triethoxysilane (APTES) as the functional monomer, tetraethoxysilane (TEOS) as the cross-linker, and vanillin as the template.

Silica/chitosan core–shell hybrid-microsphere-supported CuI catalyst for terminal alkyne homocoupling reaction

A new microfluidic approach to prepare silica/chitosan core–shell hybrid microspheres was developed. The hybrid microspheres exhibit improved mechanics and adsorption properties. In addition, the silica/chitosan-supported CuI is an outstanding catalyst for terminal alkyne homocoupling reaction. Because there is chitosan with a large amount of –NH2, which has a strong force with metal ions, on the shell of the microspheres, the chitosan can effectively reduce mass transfer resistance. Meantime, the chitosan can adsorb reactants and subsequently increase the reactant concentration around the catalyst. These two reasons make this solvent-free reaction complete within 10min at room temperature. It is easy to recover the catalyst simply through sedimentation by centrifuge. Furthermore, the silica/chitosan-supported catalyst can be reused many times with high catalytic activity.

A novel microfluidic approach for preparing chitosan-silica core-shell hybrid microspheres with controlled structures and their catalytic performance.

A facile microfluidic approach to prepare chitosan-silica core-shell hybrid microspheres with different pore structures has been developed. The hybrid microspheres showed good performance in mechanics and adsorption and are outstanding and green catalyst supports. Under optimum conditions, the adsorption capacity of Cu(ii) is about 1.7 times that of chitosan-silica hybrid microspheres with uniform component distribution for the effective protection of -NH2 provided by the silica shell while the mechanical intensity is about 2 times that of porous chitosan microspheres. Furthermore, when the adsorbed Cu(ii) is reduced to Cu(i), the chitosan-silica supported Cu(i) will be an outstanding catalyst for azide-alkyne cycloaddition reaction and the reaction can complete in water within 3 h at room temperature. The catalyst was easy to be recovered just through sedimentation by gravity or filtration. Further, the chitosan-silica supported catalyst can be reused many times without losing its activity and it can be reproducible when the catalytic activity decreases. The whole process is green, environmentally friendly and atom economic.

Synthesis and Characterization of TiO<sub>2</sub>/ PSt/PVP Multilayer Core-Shell Hybrid Microspheres

Multiplayer core-shell TiO2/PSt/PVP hybrid microspheres were successfully synthesized by the copolymerization of vinylpyrrolidone in the solution of ethyl acetate with TiO2/PSt core-shell hybrid microspheres which were formed through the encapsulation of KH570-g-TiO2 sol particles with styrene, while the active KH570-g-TiO2 sol particles were prepared by the hydrolysis condensation of KH-570 with tetrabutyl titanate. Characterization technologies of FT-IR and TGA were applied to investigate the structure and the thermal stability of the product. The results showed that the hydroxyl groups from the hydrolysis of KH-570 condensed with the surface hydroxyl groups of TiO2, as well as PSt and PVP were grafted successively onto the surface of KH570-g-TiO2 sol particles. The thermal decomposition temperature of TiO2/PSt/PVP was higher than TiO2/PSt, which also indicated that the obtained product was the final objective product.

Up-Conversion Cell Imaging and pH-Induced Thermally Controlled Drug Release from NaYF4:Yb3+/Er3+@Hydrogel Core–Shell Hybrid Microspheres

In this study, we report a new controlled release system based on up-conversion luminescent microspheres of NaYF(4):Yb(3+)/Er(3+) coated with the smart hydrogel poly[(N-isopropylacrylamide)-co-(methacrylic acid)] (P(NIPAM-co-MAA)) (prepared using 5 mol % of MAA) shell. The hybrid microspheres show bright up-conversion fluorescence under 980 nm laser excitation, and turbidity measurements show that the low critical solution temperature of the polymer shell is thermo- and pH-dependent. We have exploited the hybrid microspheres as carriers for Doxorubicin hydrochloride (DOX) due to its stimuli-responsive property as well as good biocompatibility via MTT assay. It is found that the drug release behavior is pH-triggered thermally sensitive. Changing the pH to mildly acidic condition at physiological temperature deforms the structure of the shell, causing the release of a large number of DOX from the microspheres. The drug-loaded microspheres exhibit an obvious cytotoxic effect on SKOV3 ovarian cancer cells. The endocytosis process of drug-loaded microspheres is observed using confocal laser scanning microscopy and up-conversion luminescence microscopy. Meanwhile, the as-prepared NaYF(4):Yb(3+)/Er(3+)@SiO(2)@P(NIPAM-co-MAA) microspheres can be used as a luminescent probe for cell imaging. In addition, the extent of drug release can be monitored by the change of up-conversion emission intensity. These pH-induced thermally controlled drug release systems have potential to be used for in vivo bioimaging and cancer therapy by the pH of the microenvironment changing from 7.4 (normal physiological environment) to acidic microenvironments (such as endosome and lysosome compartments) owing to endocytosis.

Reparation of silica/poly(methacrylic acid)/poly(divinylbenzene-co-methacrylic acid) tri-layer microspheres and the corresponding hollow polymer microspheres with movable silica core

Hollow poly(divinylbenzene-co-methacrylic acid) (P(DVB-co-MAA)) microspheres were prepared by the selective dissolution of the non-crosslinked poly(methacrylic acid) (PMAA) mid-layer in ethanol from the corresponding silica/PMAA/P(DVB-co-MAA) tri-layer hybrid microspheres, which were afforded by a three-stage reaction. Silica/PMAA core-shell hybrid microspheres were prepared by the second-stage distillation polymerization of methacrylic acid (MAA) via the capture of the oligomers and monomers with the aid of the vinyl groups on the surface of 3-(methacryloxy)propyl trimethoxysilane (MPS)-modified silica core, which was prepared by the Stöber hydrolysis as the first stage reaction. The tri-layer hybrid microspheres were synthesized by the third-stage distillation precipitation copolymerization of functional MAA monomer and divinylbenzene (DVB) crosslinker in presence of silica/PMAA particles as seeds, in which the efficient hydrogen-bonding interaction between the carboxylic acid groups played as a driving force for the construction of monodisperse hybrid microspheres with tri-layer structure. The morphology and the structure of silica core, silica/PMAA core-shell particles, the tri-layer hybrid microspheres and the corresponding hollow polymer microspheres with movable silica cores were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS).

Synthesis of titania/polymer core-shell hybrid microspheres

Monodisperse titania/polymer core-shell microspheres were prepared by a two-stage reaction with titania as core and poly(ethyleneglycol dimethacrylate) (PEGDMA) as shell, in which the titania cores were synthesized by a sol-gel method and subsequently grafted with 3-trimethoxysilyl methacrylate as the first-stage reaction to incorporate the vinyl groups on the surface of inorganic core. The PEGDMA shell was then encapsulated over the MPS-modified titania core by distillation precipitation polymerization of ethyleneglycol dimethacrylate in neat acetonitrile during the second-stage polymerization via capture of the radicals of EGDMA with the aid of the reactive vinyl groups on the surface of inorganic core without any stabilizer or surfactant. The shell thickness of the core-shell hybrid microspheres was controlled by the feed of EGDMA monomer during the polymerization. The resultant titania particles and core-shell microspheres were studied by transmission electron microscopy, Fourier-transform infrared spectra, X-ray photoelectron spectroscopy, and thermogravimetric analysis.

Synthesis of tri-layer hybrid microspheres with magnetic core and functional polymer shell

Tri-layer magnetite/silica/poly(divinylbenzene) (Fe 3O 4/SiO 2/PDVB) core-shell hybrid microspheres were prepared by distillation precipitation polymerization of divinylbenzene (DVB) in the presence of magnetite/3-(methacryloxyl)propyl trimethoxysilane (MPS) modified silica core-shell particles as seeds. The polymerization of DVB was performed in neat acetonitrile with 2,2′-azobisisobutyronitrile (AIBN) as initiator to coat magnetite/MPS-modified silica particles through the capture of DVB oligomers with the aid of vinyl groups on the surface of inorganic seeds in absence of any stabilizer or surfactant. Other magnetite/silica/polymer tri-layer hybrid particles, such as magnetite/silica/poly(ethyleneglycol dimethacrylate) (Fe 3O 4/SiO 2/PEGDMA) and magnetite/silica/poly(ethyleneglycol dimethacrylate- co-methacrylic acid) (Fe 3O 4/SiO 2/P(EGDMA- co-MAA)) with various polarity and functionality, were also prepared by this procedure. Magnetite/silica/poly( N,N′-methylenebisacrylamide- co-methacrylic acid) (Fe 3O 4/SiO 2/P(MBAAm- co-MAA)) were synthesized with unmodified magnetite/silica particles as seeds. The resultant tri-layer hybrid particles were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), dynamic light scattering, and vibrating sample magnetometer (VSM).

Preparation of PS/TiO 2/UF multilayer core–shell hybrid microspheres with high stability

In this paper, we report a facile method for preparation of polystyrene/titania/urea–formaldehyde resin (PS/TiO 2/UF) multilayer core–shell hybrid microspheres with high stability through in situ condensation polymerization. The TEM images show that the thickness of UF shells is about 10 nm. The Zeta potential is close to zero. The density of PS/TiO 2/UF could be controlled to 1.85 g/cm 3, which matches well with the non-polar dispersant (tetrachloroethylene). They are well dispersed and remain non-agglomerated even over several months, so they could be potential building blocks to fabricate electrophoretic display. Some parameters such as the ratio of urea–formaldehyde prepolymer (UFP) to PS/TiO 2, the pH value, and the temperature are also investigated.

Preparation of silica/polymer hybrid microspheres and the corresponding hollow polymer microspheres with functional groups

AbstractMonodisperse functional silica/polymer core–shell hybrid microspheres were prepared by a two‐stage reaction with silica grafting of 3‐(methacryloxy)propyl trimethoxysiliane (MPS) as core and polymer as shell having various functional groups such as chloromethyl, pyridyl, carboxylic acid, hydroxyl, and ester. MPS‐modified silica core was synthesized by the Stöber method and subsequently grafted with MPS as the first‐stage reaction. The functional polymer shell was then encapsulated over the MPS‐modified silica by distillation precipitation copolymerization of divinylbenzene (DVB) as a crosslinker and comonomers with different functional groups, including chloromethylstyrene (CMSt), vinyl pyridine (VPy), methacrylic acid (MAA), 2‐hydroxyethylmethacrylate (HEMA), ethyl methacrylate (EMA), ethyleneglycol dimethacrylate (EGDMA), and trimethylol propanetrimethacrylate (Trim), in neat acetonitrile with 2,2′‐azobisisobutyronitrile (AIBN) as an initiator. The encapsulation of the functional polymer shell onto the MPS‐modified silica core particles was driven by the capture of oligomer radicals the vinyl groups on the surface of the MPS‐modified silica cores during the second‐stage distillation precipitation copolymerization in the absence of any stabilizer or surfactant. The functionality and the shell thickness of the inorganic/polymer core–shell hybrid particles were controlled by the amount of DVB crosslinker and the functional comonomers during the copolymerization. The corresponding hollow polymer microspheres with various functional groups, including chloromethyl, pyridyl, carboxylic acid, and ester groups were further developed after the selective removal of silica core with hydrofluoric acid. The functional core–shell silica/polymer hybrid microspheres and the corresponding functional hollow polymer microspheres were characterized with transmission electron microscopy (TEM) and Fourier transform infrared spectra (FT‐IR). Copyright © 2008 John Wiley & Sons, Ltd.

Facile synthesis of silica/polymer hybrid microspheres and hollow polymer microspheres

Monodisperse silica/polydivinylbenzene (SiO2/PDVB) and silica/poly(ethyleneglycol dimethacrylate) (SiO2/PEGDMA) core–shell hybrid microspheres were prepared by a two-stage reaction with silica particles' grafting of 3-(methacryloxy)propyltrimethoxysilane (MPS) as core and PDVB or PEGDMA as shell, in which the MPS-modified silica core with diameter of 238nm was synthesized by Stöber method and subsequently grafted with MPS as the first-stage reaction. The PDVB or PEGDMA shell was then encapsulated over the MPS-modified silica core by distillation precipitation polymerization of divinylbenzene (DVB) or ethyleneglycol dimethacrylate (EGDMA) in neat acetonitrile with 2,2′-azobisisobutyronitrile (AIBN) initiator as the second-stage reaction. The encapsulation of PDVB and PEGDMA on modified silica core particles was driven by the capture of DVB or EGDMA oligomer radicals via the vinyl groups on the surface of the modified silica cores during the second-stage polymerization in the absence of any stabilizer or surfactant. The shell thickness of the core–shell hybrid particles was controlled by the feed of DVB or EGDMA monomer during the polymerization. Hollow PDVB or PEGDMA microspheres with various shell thickness were further developed after selective removal of the modified silica cores with hydrofluoric acid. The resultant core–shell hybrid materials and hollow microspheres were characterized by transmission electron microscopy (TEM), and Fourier transform infrared spectra (FT-IR).

Facile Preparation Method of SiO2/PS/TiO2 Multilayer Core−Shell Hybrid Microspheres

Organic-inorganic hybrid particles have many potential applications, but almost all of this research was focused on the hybrid particles containing one kind of inorganic nanoparticles. This paper presented a facile preparation method for SiO2/PS/TiO2 multilayer core-shell hybrid microspheres. In this approach, positively charged SiO2/PS core-shell hybrid particles were first synthesized by miniemulsion polymerization using cationic initiator and emulsifier. These positively charged SiO2/PS hybrid particles were mixed with tetra-n-butyl titanate for sol-gel reaction to directly form SiO2/PS/TiO2 multilayer core-shell hybrid microspheres. Some influencing parameters such as surfactant concentration, tetra-n-butyl titanate amount, and glacial acetic acid amount were investigated. TEM, TGA, and EDX analyses indicated that titania layers were successfully coated onto the surfaces of hybrid microspheres.

ZnO/PS core–shell hybrid microspheres prepared with miniemulsion polymerization

The hybrid microspheres of ZnO/PS with different core–shell structures were prepared in miniemulsion polymerization. 3-(trimethoxysilyl)propyl methacrylate (MPS) was used as a functional comonomer to enhance the surface polarity of ZnO nanoparticles and to prevent water from quenching the luminescent properties of ZnO. The morphology of hybrid particles was examined with a transmission electron microscope. The luminescence spectra were measured using a Shimadzu RF-5301 PC spectrofluorimeter (Xe source) at room temperature. The crystallization structure of samples was characterized with a Rigaku wide-angle X-ray diffractometer. The chemical composition and structure of the ZnO colloids, MPS-modified ZnO colloids, and ZnO/PS hybrid microspheres were analyzed with IR.