Synthesis of bifunctional core–shell particles with a porous zeolite core and a responsive polymeric shell

The aim of our work is the synthesis and characterization of colloidal core–shell particles with a zeolite core and an environmentally responsive shell. We have synthesized colloidal ZSM-5 zeolite and modified the surface with 3-(trimethoxysilyl)propyl methacrylate in order to introduce double bonds at the surface. The cross-linked polymeric shell was prepared by precipitation polymerization using the functionalized zeolite particles as seeds. We employed thermoresponsive poly(N-isopropylacrylamide) and pH-responsive poly(vinylpyridine) as the polymeric shell, respectively. The temperature- and pH-depending swelling and deswelling of the core–shell particles were characterized with dynamic light scattering techniques. Transmission electron microscopy pictures show the morphology of the synthesized particles. It is proposed that these types of bifunctional core–shell particles could be of use for controlled uptake and release applications and separation of molecules.     

Synthesis and photocatalytic properties of core–shell TiO~2@ZnIn_2S_4 photocatalyst

A novel core–shell TiO2@ZnIn2S4composite has been synthesized successfully by a simple and flexible hydrothermal route using TiO2as precursors.The as-synthesized samples were characterized by X-ray diffraction,UV–vis diffuse reflectance spectra and transmission electron microscopy.The photocatalytic properties of samples were tested by degradation of aqueous methylene blue（MB）under visible light irradiation.It was found that the as-synthesized TiO2@ZnIn2S4photocatalyst was more effcient than TiO2and ZnIn2S4in the photocatalytic degradation of MB.Moreover,TEM images confrmed the TiO2@ZnIn2S4nanoparticles possessed a well-proportioned core–shell morphology.     

X-ray imaging of newly-developed gadolinium compound/silica core–shell particles

A preparation method for gadolinium compound (Gd) nanoparticles coated with silica (Gd/SiO₂) is proposed. Gd nanoparticles were prepared with a homogeneous precipitation method at 80 °C using 1.0 × 10⁻³ M Gd(NO₃)₃ and 0.5 M urea in the presence of 1.0 g/L stabilizer. Among stabilizers examined. Sodium n-dodecyl sulfate (SDS) was suitable as the stabilizer for preparing small Gd nanoparticles, and consequently Gd nanoparticles with a size of 46.2 ± 12.4 nm were prepared using the SDS. Silica-coating of the Gd nanoparticles was performed by a St?ber method at room temperature using 0.013 M TEOS and 2.0 × 10⁻³ M NaOH in water/1-propanol solution in the presence of 1.0 × 10⁻³ M Gd nanoparticles, which resulted in production of Gd/SiO₂ particles with an average size of 64.2 ± 14.4 nm. The Gd/SiO₂ particles were surface-modified with 3-aminopropyltrimethoxysilane and succinic anhydride. It was confirmed by measurement of electrophretic light scattering that amino group or carboxyl group was introduced onto the Gd/SiO₂ particles. The gadolinium concentration of 1.0 × 10⁻³ M in the as-prepared colloid solution was increased up to a gadolinium concentration of 0.4 M by centrifugation. The core–shell structure of Gd/SiO₂ particles was undamaged, and the colloid solution was still colloidally stable, even after the concentrating process. The concentrated Gd/SiO₂ colloid solution showed an X-ray image with contrast as high as a commercial Gd complex contrast agent. Internal organs in a mouse could be imaged injecting the concentrated colloid solution into it.     

The volume transition in thermosensitive core–shell latex particles containing charged groups

An investigation of the volume transition in thermosensitive core–shell particles by dynamic light scattering (DLS) is presented. The core of the particles consists of polystyrene (diameter 118 nm), whereas the thermosensitive shell is composed of a network of poly (N-isopropylacrylamide) containing 2 mol% acrylic acid counits. The hydrodynamic radius of these particles as determined by DLS decreases in a continuous manner when raising the temperature. It is shown that the volume transition in the core–shell microgels remains continuous for a wide range of ionic strengths and pH values. This behavior is opposite to that of macrogels of the same chemical composition, which undergo a discontinuous volume transition. The present investigation therefore demonstrates that affixing the network to solid colloidal particles profoundly alters the volume transition of thermosensitive networks. The reason is that shrinking can take place only along the radial direction of the particles. The solid core thus exerts a strong spatial constraint onto the network, which leads to the observed behavior. Received: 29 March 1999 Accepted in revised form: 16 July 1999     

Preparation of titania hollow particles with independently controlled void size and shell thickness by catalytic templating core–shell polymer particles

Organic/inorganic hybrids were prepared by catalytic hydrolysis and subsequent polycondensation of tetra-n-butyl titanate (TnBT) in shell layers grafted on core particles. The core particles were synthesized by emulsifier-free emulsion polymerization of styrene, N-n-butyl-N-2-methacryloyloxyethyl-N,N-dimethylammonium bromide (C₄DMAEMA), and 2-chloropropionyloxyethyl methacrylate using 2,2′-azobis(2-amidinopropane) dihydrochloride as an initiator. The core diameters were controlled in the range of 70–550 nm by adjusting a C₄DMAEMA feed concentration. The core–shell particles were prepared by surface-initiated activator generated electron transfer–atom transfer radical polymerization of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA). The sizes of core–shell particles were found to increase monotonically with an increase in a DMAEMA concentration. The hybrid particles were fabricated by adding TnBT into a water/ethanol dispersion of core–shell particles. The amounts of titania deposited increased in proportion to the grafted amounts of poly[2-(N,N-dimethylamino)ethyl methacrylate] on the core particles. The X-ray diffraction measurement revealed that the hollow titania particles obtained by heat treatment of hybrids have an anatase crystallographic phase.     

Thermoresponsive submicron-sized core–shell hydrogel particles with encapsulated olive oil

Thermoresponsive submicron-sized core–shell hydrogel particles with incorporated olive oil were synthesised and studied. The microspheres having poly(N-isopropylacrylamide-co-methyl methacrylate) core and poly(N-isopropylacrylamide) shell were synthesised by emulsifier-free seed polymerisation method. The morphology, particle size and distribution characteristics of the core microspheres were studied with different amount of initiator, monomer–solvent ratio and polymerisation time using scanning electron microscopy and dynamic light scattering particle size analysis. The prepared core and core–shell microspheres were regularly spherical with average size of around 190.0 and 320.0 nm respectively and nearly monodispersed size distribution. Transmission electron microscopy study revealed the core–shell structure of the microspheres. The thermoresponsive transition temperature (T _t) of the core–shell microspheres was determined as 33 °C by optical absorbance measurement, dynamic light scattering particle size analysis and differential scanning calorimetry. The release rate of olive oil from core–shell microspheres was accelerated by squeezing out the entrapped olive oil as the temperature was increased above T _t. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy study indicated the formation of copolymer.     

Biomimetic synthesis of raspberry-like hybrid polymer–silica core–shell nanoparticles by templating colloidal particles with hairy polyamine shell

The nanoparticles composed of polystyrene core and poly[2-(diethylamino)ethyl methacrylate] (PDEA) hairy shell were used as colloidal templates for in situ silica mineralization, allowing the well-controlled synthesis of hybrid silica core–shell nanoparticles with raspberry-like morphology and hollow silica nanoparticles by subsequent calcination. Silica deposition was performed by simply stirring a mixture of the polymeric core–shell particles in isopropanol, tetramethyl orthosilicate (TMOS) and water at 25 °C for 2.5 h. No experimental evidence was found for nontemplated silica formation, which indicated that silica deposition occurred exclusively in the PDEA shell and formed PDEA–silica hybrid shell. The resulting hybrid silica core–shell particles were characterized by transmission electron microscopy (TEM), thermogravimetry, aqueous electrophoresis, and X-ray photoelectron spectroscopy. TEM studies indicated that the hybrid particles have well-defined core–shell structure with raspberry morphology after silica deposition. We found that the surface nanostructure of hybrid nanoparticles and the composition distribution of PDEA–silica hybrid shell could be well controlled by adjusting the silicification conditions. These new hybrid core–shell nanoparticles and hollow silica nanoparticles would have potential applications for high-performance coatings, encapsulation and delivery of active organic molecules.     

Electrical surface charge and potential of hematite/yttrium oxide core–shell colloidal particles

Interest in the synthesis of composite colloidal particles consisting of a core and shell with different compositions stems from the fact that such particles can be useful in processes where the properties of both core (e.g., size and shape homogeneity, ease of preparation in large amounts, magnetic characteristics, etc.) and shell (interfacial properties, porosity, chemical stability, etc.) might be of interest. However, the applicability must be based on a proper characterization of those properties. In this work, colloidal spheres of hematite (α-Fe₂O₃) were used as nuclei of mixed particles where the shell is yttrium oxide. The electrical properties of the aqueous interface are compared to those of the pure oxides by means of potentiometric titration of their surface charge and potential against pH, as a function of indifferent electrolyte concentration. It is found that the mixed particles efficiently mimic yttrium oxide, since the behavior of their surface electrical characteristics closely resembles that of the latter compound. Differences are found, however, that can be ascribed to an incomplete or porous coverage, but such divergences are of little significance when an overall comparison is carried out. Received: 30 January 2001 Accepted: 11 July 2001     

Morphology and film formation of poly(butyl methacrylate)–polypyrrole core–shell latex particles

 Core–shell latex particles made of a poly(butyl methacrylate) (PBMA) core and a thin polypyrrole (PPy) shell were synthesized by two-stage polymerization. In the first stage, PBMA latex particles were synthesized in a semicontinuous process by free-radical polymerization. PBMA latex particles were labeled either with an energy donor or with an energy acceptor, in two different syntheses. These particles were used in a second stage as seeds for the synthesis of the core–shell particles. The PPy shell was polymerized around the PBMA core latex in an oxidative chemical in situ polymerization. Proofs for the success of the core–shell synthesis were obtained using nonradiative energy transfer (NRET) and atomic force microscopy (AFM). NRET gives access to the rate of polymer chain migration between adjacent particles in a film annealed at a temperature above the glass-transition temperature T _g of the particles. Slower chain migration of the PBMA polymer chains was obtained with the PBMA–PPy core–shell particles compared to rate of the PBMA polymer chain migration found with the pure, uncoated PBMA particles. This result is due to the coating of PBMA by PPy, which hinders the migration of the PBMA polymer chains between adjacent particles in the film. This observation has been confirmed by AFM measurements showing that the flattening of the latex film surface is much slower for the core–shell particles than for the pure PBMA particles. This result can again be explained by the presence of a rigid PPy shell around the PBMA core. Thus, these two complementary methods have given evidence that real core–shell particles were synthesized and that the shell seriously hinders film formation of the particles in spite of the fact that it is very thin (thickness close to 1 nm) compared to the size (750 and 780 nm in diameter) of the PBMA core. Transparency measurements confirm the results obtained by NRET and AFM. When the films are placed at a temperature higher than the T _g of PBMA, the increase in transparency is faster for films made with the uncoated PBMA particles than for films made with the coated PBMA particles. This result indicates again that the presence of the rigid PPy layer around the PBMA core reduces considerably the speed at which the structure of the film is modified when heated above the T _g of PBMA. Received: 02 September 1999 Accepted: 21 December 1999     

α-Fe2O3@carbon core–shell nanostructure for luminescent upconversion and photocatalytic degradation of methyl orange

Research on Chemical Intermediates - The unique characteristics of metal–organic frameworks such as structural tunability, high surface area, low density, and tailored porosity have made this...     

Preparation of core–shell composite polymer particles by a novel heterocoagulation based on hydrophobic interaction

Submicron-sized cationic polystyrene shell particles with active ester groups were effectively self-assembled on hydrophobic surfaces of cross-linked polystyrene (PST) particles, uncharged core particles with ca. 8.5-µm diameter in aqueous systems. The hydrophobic interactions between the shell particles and core particles play a key role in heterocoagulation. The resulting heterocoagulates were highly physically stable in water, and the morphology was controlled by several factors including the solid content of latex, self-assembling time, and electrolyte concentration. Composite polymer particles with a core–shell structure were successfully obtained from the heterocoagulates by heat treatment for 3 h at a temperature above the glass transition temperature (T_g) of the cationic polymer shell particles.     

Sol–gel synthesis of porous inorganic materials using “core–shell” latex particles as templates

Here we report on the sol–gel synthesis of porous inorganic materials based on manganese, molybdenum, and tungsten compounds using the “core–shell” siloxane-acrylate latex as a template. The chemical composition and structural characteristics of the materials obtained have been investigated. It was shown that temperature conditions and gaseous media composition during the template destruction controlled the composition and structure of porous materials. To obtain porous inorganic materials for catalytic applications, the “core–shell” latex template was preliminarily functionalized by gold and palladium nanoparticles obtained by thermal reduction of noble metal ions-precursors in a polycarboxylic “shell”. Upon the template removal, noble metals nanoparticles of a size of dozens of nanometers were homogeneously distributed in the material porous structure. The evaluation of the catalytic activity of macroporous manganese, tungsten, and molybdenum oxides under the conditions of liquid phase catalytic oxidation of organic dyes has been performed. The prospects of employing macroporous oxide systems with immobilized nanoparticles of noble metals in the processes of hydrothermal oxidation of radionuclide organic complexes in radioactive waste decontamination have been demonstrated.     

Controlled preparation of core–shell polystyrene/polypyrrole nanocomposite particles by a swelling–diffusion–interfacial polymerization method

Polystyrene/polypyrrole (PS/PPy) core–shell nanocomposite particles with uniform and tailored morphology have been successfully synthesized using the “naked” PS particulate substrate with the aid of a proposed strategy, the so-called swelling–diffusion–interfacial polymerization method. After initially forming pyrrole-swollen PS particles, diffusion of the monomer toward the aqueous phase was controlled through the addition of hydrochloric acid, eventually leading to its polymerization on the substrate particle surface. This process allows the nanocomposite particles to possess uniform and intact PPy overlayer and affords much more effective control over the structure and morphology of the resultant nanocomposites by simply changing the PS/pyrrole weight ratio or the addition amount of the doping acid. In particular, the nanocomposite particles with a thin, uniform, and intact PPy overlayer and their corresponding PPy hollow particles were obtained at a low addition amount of pyrrole. The resultant nanocomposite particles have been extensively characterized using scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetry.     

Poly(styrene-b-ethylene oxide) copolymers as stabilizers for the synthesis of silica–polystyrene core–shell particles

Following previous works [1, 2], silica–polystyrene core–shell particles have been synthesized by dispersion polymerization of styrene in an ethanol/water mixture in the presence of a poly(styrene-b-ethylene oxide) block copolymer as stabilizer. Besides the formation of composite core–shell particles, a large number of free latex particles that do not contain silica were also formed. This number decreases as the size of the silica beads decreases from 300 to 29 nm in diameter, and becomes very low compared to the number of composite particles for the smallest silica beads used. In every case, the composite particles could be easily separated from the free latex particles by centrifugation, providing a material made of regular core–shell composite particles. On the basis of the mechanisms involved in dispersion polymerization, hypotheses were formulated to account for the formation of the silica–polystyrene composite particles. Received: 6 May 1999 Accepted in revised form: 29 June 1999     

Amphiphilic polymeric particles with core–shell nanostructures: emulsion-based syntheses and potential applications

The design and synthesis of amphiphilic nano- to micro-sized polymeric particles with core–shell nanostructures have attracted more and more attention because of their wide applicability in modern material science and their technological importance in the areas of colloid and interface science. Many synthetic strategies have been developed for the preparation of amphiphilic core–shell particles that consist of hydrophobic polymer cores and hydrophilic polymeric shells. In this review, we focus on emulsion-based approaches and properties of particles produced. These methods are: (1) grafting to functionalized particle that produces a corona-like particle, (2) grafting from reactive seed particle that produces a brush-like particle, (3) copolymerization of reactive macro-monomer with hydrophobic monomer that produces a corona-like particle, (4) emulsion polymerization in the presence of block or comb-like copolymer containing controlled free-radical moiety that produces a multi-layered particle, and (5) redox-initiated graft polymerization of vinyl monomer from a water-soluble polymer containing amino groups that produces a hairy-like particle. Potential applications of some of these particles in drug and gene deliveries, enzyme immobilization, colloidal nanocatalyst, chemical sensing, smart coating, and thermal laser imaging will be discussed.     

Modified reverse microemulsion synthesis for iron oxide/silica core–shell colloidal particles

Iron oxide/silica core–shell colloidal particles were prepared by basic reverse microemulsion (RM) method and two modified RM methods. By basic RM method, maximum particle size obtained was mere 40 nm. For building photonic crystals working in the visible range, the colloidal particles must be larger than 100 nm. Thus two modified RM methods were used. By alcohol modified RM method, short chain alcohols were used as co-surfactant. The particle size rose to near 100 nm, but the core–shell structure was comparatively poor. By emulsifier pair modified RM method, the particle size leapt to over 200 nm and a narrow growth window was found favorable to enhance the stability and rigidity of the surfactants layers. The core–shell mechanism was also discussed and a new four-step mechanism was proposed.     

Electrochemical determination of the surface composition of Pd–Pt core–shell nanoparticles

Different amounts of Pt atoms were deposited onto the surface of Pd nanoparticles supported on carbon black by hydroquinone reduction method in anhydrous ethanol. Here, we surveyed electrochemical probing of surface compositions of Pd–Pt surface alloys. They were calculated from hydrogen desorption, carbon monoxide adlayer oxidation, and reduced carbon dioxide oxidation charges. The surface composition of Pt drastically increased up to Pt[0.3]/Pd/C (23.1 at.% of Pt) and then approached that of pure Pt with the moderate rate of increase.     

Synthesis of high-quality core–shell quantum dots of CdSe–CdS by means of gradual heating in liquid paraffin

Here, we report a novel strategy to prepare fluorescent semiconductor quantum dots (QDs) of core–shell type with CdSe–CdS QDs as a model system. Our synthesis was carried out in liquid paraffin, which is a natural, nontoxic, and cheap solvent. We applied a single injection of precursor for the shell growth at low temperature and gradual heating of the reaction mixture after that. By this manner, the Ostwald ripening of the cores was reduced, homogenous nucleation of the shell material was avoided, and highly monodisperse in size core–shell QDs were prepared. Our synthesis method allows working on open air; it is relatively fast and allows fine control over the shell growth process. It leads to the formation of core–shell CdSe–CdS QDs with fluorescence quantum yield as high as 65%. We described the optical properties of core–shell QDs by the model of attenuated quantum confinement.     

Fabrication of polymeric micelles with core–shell–corona structure for applications in controlled drug release

Thermo-responsive polymeric micelles of poly (ethylene glycol)-b-poly(2-hydroxyethyl methacrylate-g-lactide)-b-poly(N-isopropylacrylamide) (PEG-P(HEMA-PLA)-PNIPAM) with core–shell–corona structure were fabricated for applications in controlled drug release. The graft copolymer of PEG-P(HEMA-PLA)-PNIPAM was self-assembled into core–shell micelles with a densely PLA core and mixed PEG/PNIPAM shells at 25 °C in aqueous media. By increasing the temperature above the lower critical solution temperature of PNIPAM, these core–shell micelles could be converted into core–shell–corona micelles because of the collapse of PNIPAM block on the PLA core as the inner shell and the soluble PEG block stretching outside as the outer corona. Anticancer drug doxorubicin (DOX) was loaded in the polymeric micelles as a model drug. Compared with polymeric micelles formed by liner PEG-b-PLA-b-PNIPAM triblock copolymer, these polymeric micelles exhibited higher loading capacity, and release of DOX from the polymeric micelles with core–shell–corona structure was well-controlled.