Deformable hollow hybrid silica/siloxane colloids by emulsion templating

A procedure to obtain hollow colloidal particles has been developed using an emulsion templating technique. Monodisperse silicone oil droplets were prepared by hydrolysis and polymerization of dimethyldiethoxysilane monomer and incorporated in a solid shell using tetraethoxysilane. Hollow shells were obtained by exchange of the core. The formation of the oil droplets was investigated using static light scattering and 29Si solution NMR, and the hollow shells were characterized by electron microscopy and static light scattering. Details on the composition of the shell material were obtained from energy-dispersive X-ray analysis and 29Si solid state NMR, revealing that the shells consist of a hybrid cross-linked network of silica and siloxane units. Confocal microscopy was used to show that the shells are permeable to small dye molecules. The thickness of the coating can be easily varied from a few nanometers upward. Depending on the ratio of shell thickness to particle radius, three types of hollow shells can be distinguished depending on the way in which they buckle upon drying. We designate them as microspheres, microcapsules, and microballoons. As a result of their monodispersity, these particles can be used for making 3D-ordered materials.     

Synthesis and utilization of monodisperse hollow polymeric particles in photonic crystals

We developed a process to fabricate 150-700 nm monodisperse polymer particles with 100-500 nm hollow cores. These hollow particles were fabricated via dispersion polymerization to synthesize a polymer shell around monodisperse SiO(2) particles. The SiO(2) cores were then removed by HF etching to produce monodisperse hollow polymeric particle shells. The hollow core size and the polymer shell thickness, can be easily varied over significant size ranges. These hollow polymeric particles are sufficiently monodisperse that upon centrifugation from ethanol they form well-ordered close-packed colloidal crystals that diffract light. After the surfaces are functionalized with sulfonates, these particles self-assemble into crystalline colloidal arrays in deionized water. This synthetic method can also be used to create monodisperse particles with complex and unusual morphologies. For example, we synthesized hollow particles containing two concentric-independent, spherical polymer shells, and hollow silica particles which contain a central spherical silica core. In addition, these hollow spheres can be used as template microreactors. For example, we were able to fabricate monodisperse polymer spheres containing high concentrations of magnetic nanospheres formed by direct precipitation within the hollow cores.     

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.     

Diffusion through colloidosome shells

Colloidosomes are aqueous cores surrounded by a shell composed of packed colloidal particles. Recent studies suggest that these colloidal shells reduce, or even inhibit, the transport of molecular species (diffusants). However, the effect of the colloidal shell on transport is unclear: In some cases, the reduction in transport of diffusants through the shell was found to be independent of the size of the colloidal particles composing the shell. Other studies find, however, that shells composed of small colloidal particles of order 100nm or less hindered transport of diffusants more than those composed of micro-scale colloidal particles. In this paper we present a simple diffusion model that accounts for three processes that reduce diffusant transport through the shell: (i) a reduction in the penetrable volume available for transport, which also increases the tortuousity of the diffusional path, (ii) narrow pore size which may hinder transport for larger diffusants through size exclusion, and (iii) a reduction in interfacial area due to 'blocking' of the surface by the adsorbed particles. We find that the colloidal particle size does not affect the reduction in transport through the colloidal shell when the shell is a monolayer. However, in closely packed, thick layers where the thickness of the multi-layer shell is fixed, the rate of transport decreases significantly with colloidal particle dimensions. These results are in excellent agreement with previously published experimental results.     

具有疏水核/亲水壳的双亲胶体粒子的制备

制备了具有疏水性聚苯乙烯核/亲水性聚丙烯酰胺壳的双亲粒子.疏水核通过超浓乳液聚合制备,亲水壳层通过过氧化羟基异丙苯和硫酸亚铁的界面引发制备.控制条件可得到网孔(半包覆)、褶皱(全包覆)两种形态的壳层.壳层孔的存在使得核层聚合物能够与外界接触.粒子的双亲性通过吸水吸油率进行表征.     

Transport through self-assembled colloidal shells (colloidosomes)

Colloidosomes, namely, microcapsules coated by a colloidal shell, have been widely studied as potential carriers of active compounds for various applications. The colloidal shell differs from the shells of other ‘somes’ (liposomes, polymersomes) since it is a composite material with an impenetrable phase—the particles, and a penetrable one—the voids or pores between them. Recent analysis shows that in the shells composed of monodisperse and charged particles, the maximal volume fraction of colloids in the self-assembled layer depends on the size ratio between the particle's hard-sphere radius and the effective radius, which includes the range of repulsive electrostatic interactions. Thus, somewhat counter-intuitively, the density of particles in the shell increases with increasing particle radius. However, mixing particle sizes can lead to highly packed shells where the impenetrable phase volume fraction approaches 100%. The diffusional flux through the colloidal shell is highly sensitive to the packing density (or particle volume fraction); this parameter sets the average size of the pores, their distribution through the shell, and their tortuosity. However, while in thick multi-layer shells the flux increases with increasing particle size, in the case of monolayer-thick shells there is no apparent dependence of the flux on the colloid dimensions.     

Characterization of polymer-silica nanocomposite particles with core-shell morphologies using Monte Carlo simulations and small angle X-ray scattering

A two-population model based on standard small-angle X-ray scattering (SAXS) equations is verified for the analysis of core-shell structures comprising spherical colloidal particles with particulate shells. First, Monte Carlo simulations of core-shell structures are performed to demonstrate the applicability of the model. Three possible shell packings are considered: ordered silica shells due to either charge-dependent repulsive or size-dependent Lennard-Jones interactions or randomly arranged silica particles. In most cases, the two-population model produces an excellent fit to calculated SAXS patterns for the simulated core-shell structures, together with a good correlation between the fitting parameters and structural parameters used for the simulation. The limits of application are discussed, and then, this two-population model is applied to the analysis of well-defined core-shell vinyl polymer/silica nanocomposite particles, where the shell comprises a monolayer of spherical silica nanoparticles. Comprehensive SAXS analysis of a series of poly(styrene-co-n-butyl acrylate)/silica colloidal nanocomposite particles (prepared by the in situ emulsion copolymerization of styrene and n-butyl acrylate in the presence of a glycerol-functionalized silica sol) allows the overall core-shell particle diameter, the copolymer latex core diameter and polydispersity, the mean silica shell thickness, the mean silica diameter and polydispersity, the volume fractions of the two components, the silica packing density, and the silica shell structure to be obtained. These experimental SAXS results are consistent with electron microscopy, dynamic light scattering, thermogravimetry, helium pycnometry, and BET surface area studies. The high electron density contrast between the (co)polymer and the silica components, together with the relatively low polydispersity of these core-shell nanocomposite particles, makes SAXS ideally suited for the characterization of this system. Moreover, these results can be generalized for other types of core-shell colloidal particles.     

Preparation and coating of finely dispersed drugs 4. Loratadine and danazol

The preparation of colloidal particles of different morphologies, including spheres, of two drugs, loratadine and danazol, is described. In principle these particles were obtained by precipitation when nonsolvents (water or aqueous surfactant solutions) were added to ethanol solutions of the drug. In addition, procedures were developed that made it possible to use the drug particles thus obtained as cores to be then coated with either silica or aluminum (hydrous) oxide layers. The presence of these inorganic shells was confirmed by electron microscopy, energy dispersive spectroscopy, and electrophoresis.     

Encapsulation of emulsion droplets by organo-silica shells

Surfactant-stabilized emulsion droplets were used as templates for the synthesis of hollow colloidal particles. Monodisperse silicone oil droplets were prepared by hydrolysis and polymerization of dimethyldiethoxysiloxane monomer, in the presence of surfactant: sodium dodecyl sulphate (SDS, anionic) or Triton X-100 (non-ionic). A sharp decrease in the average droplet radius with increasing surfactant concentration was found, with a linear dependence of the droplet radius on the logarithm of the surfactant concentration. The surfactant-stabilized oil droplets were then encapsulated with a solid shell using tetraethoxysilane, and hollow particles were obtained by exchange of the liquid core. The size and polydispersity of the oil droplets and the thickness of the shell were determined using static light scattering, and hollow particles were characterized by electron microscopy. Details on the composition of the shell material were obtained from energy-dispersive X-ray analysis. In the case of sodium dodecyl sulphate, the resulting shells were relatively thin and rough, while when Triton X-100 was used, smooth shells were obtained which could be varied in thickness from very thick ( approximately 150 nm) to very thin shells ( approximately 17 nm). Finally, hexane droplets were encapsulated using the same procedure, showing that our method can in principle be extended to a wide range of emulsions.     

Synthesis and green up-conversion fluorescence of colloidal La0.78Yb0.20Er0.02F3/SiO2 core/shell nanocrystals

Water-soluble PVP-stabilized hexagonal-phase La_0.78Yb_0.20Er_0.02F₃ nanocrystals (NCs) were synthesized by hydrothermal method. The NCs were coated with a very thin silica shell, and amino groups were introduced to the surface of silica shells by copolymerization of 3-aminopropyl(triethoxy)silane. The core/shell NCs can be dispersed in ethanol and water to form stable colloidal solution. The transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were used to characterize the core/shell materials. In addition, the green up-conversion fluorescence mechanism of La_0.78Yb_0.20Er_0.02F₃/SiO₂ NCs was studied with a 980-nm diode laser as excitation source. The water solubility, small core/shell particles size, and well colloidal stability mean the green up-conversion fluorescence NCs have potential applications in bioassay.     

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.     

Microcrystalline composite particles of carbon nanotubes and calcium carbonate

Coprecipitation of urea-melt modified carbon nanotubes and calcium carbonate from an aqueous solution by two methods yielded microcrystalline composite particles. Powders obtained by colloidal crystallization from a supersaturated solution that were isolated and dried soon after precipitation were a mixture of raspberry-shaped and rhombohedral particles. These were shown by infrared and X-ray diffraction analyses to be mainly calcite. Particles that were kept wet for 1 day or longer before being isolated were typically entirely rhombohedral with edge lengths in the range of 5-30 microm. Scanning electron microscopy investigations revealed that the nanotubes were adsorbed on the particle surface and also incorporated into the interior matrix. Removal of the calcium carbonate component by treating the particles with acid yielded nanotube shells whose size and shape reflected those of the original particles.     

Facile fabrication of core-in-shell particles by the slow removal of the core and its use in the encapsulation of metal nanoparticles

Core-in-shell particles with controllable core size have been fabricated from core-shell particles by means of the controlled core-dissolution method. These cores in inorganic shells were employed as scaffolds for the synthesis of metal nanoparticles. After dissolution of the cores, metal nanoparticles embedded in cores were encapsulated into the interior of shell, without any damage or change. This article describes a very simple method for deriving core-in-shell particles with controllable core size and encapsulation of nanoparticles into the interior of shell.     

Synthesis of binary polyelectrolyte/inorganic composite capsules of micron size

Different approaches for the synthesis of binary polyelectrolyte/inorganic layered composite capsules of micron size are described. As the polyelectrolyte part of the composite, a poly(styrene sulfonate)/poly(allylamine hydrochloride) complex was taken; the inorganic component was composed of magnetic nanoparticles (Fe₃O₄, CoFe₂O₄, MnFe₂O₄, ZnFe₂O₄), insulator nanoparticles (rare-earth fluorides) or metal nanoparticles (Ag). An inner inorganic layer was formed inside the hollow polyelectrolyte capsule via chemical or photochemical reaction in a spatially restricted capsule volume. The inorganic nanophase synthesized was characterized by transmission electron microscopy, scanning electron microscopy, and wide angle X-ray scattering techniques and weakly crystallized particles 6–9 nm in diameter were detected, presumably attached to the inner side of the capsule shell. Polyelectrolyte capsules filled with ferrite (magnetite) particles possess substantial magnetic activity and are easily manipulated in water solution by an external magnetic field.     

Synthesis and characterization of epoxy-functional polystyrene particles

Colloidal polystyrene particles with surface epoxy groups have been synthesized through surfactant-free emulsion copolymerization of styrene with glycidyl methacrylate; and through copolymerization of glycidyl methacrylate (GMA) and methyl methacrylate as shells around existing polystyrene seed particles. We developed two titration methods to quantify the number of epoxy groups that survived the polymerization processes. The styrene-GMA copolymer particles were judged to be unsatisfactory as model colloidal materials due to their size polydispersity and unknown internal distribution of epoxy groups. The core-shell particles had high epoxy surface densities with at least 60% of the initial epoxy groups surviving the synthesis process. Transmission electron microscopy shows that the thickness of the epoxy-rich shell is less than expected based on the volume of monomers added, suggesting that some of the monomer forms water-soluble oligomers. Photon correlation spectroscopy measurements imply that the shell is swollen with water and consists of polymer configurations which extend out into solution. The morphological details vary consistently with the GMA content, and hence the hydrophilicity, of the shell polymer. © 1995 John Wiley & Sons, Inc.     

Colloidal synthesis of new silver-based nanostructures with tailored localized surface plasmon resonance

Silver-based nanostructures with tailored localized surface plasmon resonance are of interest for a number of practical applications. They can conventionally be divided into three main groups: (1) anisotropic silver particles, (2) particles of alloys of silver with other metals, and (3) composite particles with dielectric or magnetic cores and silver shells. Fine “tuning” of plasmon resonance of these particles is ensured by changes in their shapes, composition, and/or structure. Procedures for the colloidal synthesis of nanostructures of all these groups and some fields of their application are described, with the main attention focused on core/shell composite particles.     

Preparation and characterization of core-shell latexes

Polymeric dispersions with a concentric core-shell structure of the latex particles were obtained by a two-stage emulsion polymerization technique. Conditions for the formation of shells on polymeric seeds are discussed. SANS and SAXS investigations were carried out in order to verify the core-shell structure of the particles. DSC and IR measurements indicate the existence of an interfacial layer between core and shell polymers. The results are transferred to emulsion polymers containing inorganic filler particles.     

Effect of colloidal particle size on adsorbed monodisperse and bidisperse monolayers

Coating hydrogel films or microspheres by an adsorbed colloidal shell is one synthesis method for forming colloidosomes. The colloidal shell allows control of the release rate of encapsulated materials, as well as selective transport. Previous studies found that the packing density of self-assembled, adsorbed colloidal monolayers is independent of the colloidal particle size. In this paper we develop an equilibrium model that correlates the packing density of charged colloidal particles in an adsorbed shell to the particle dimensions in monodisperse and bidisperse systems. In systems where the molar concentration in solution is fixed, the increase in adsorption energy with increasing particle size leads to a monotonic increase in the monolayer packing density with particle radius. However, in systems where the mass fraction of the particles in the adsorbing solutions is fixed, increasing particle size also reduces the molar concentration of particles in solution, thereby reducing the probability of adsorption. The result is a nonmonotonic dependence of the packing density in the adsorbed layer on the particle radius. In bidisperse monolayers composed of two particle sizes, the packing density in the layer increases significantly with size asymmetry. These results may be utilized to design the properties of colloidal shells and coatings to achieve specific properties such as transport rate and selectivity.     

金核银壳纳米粒子薄膜的制备及SERS活性研究

采用柠檬酸化学还原法制备金溶胶, 通过自组装技术在石英片表面制备金纳米粒子薄膜, 在银增强剂混合溶液中反应获得金核银壳纳米粒子薄膜. 用紫外-可见吸收光谱仪和原子力显微镜(AFM)研究了不同条件下制备的金核银壳纳米粒子薄膜的光谱特性和表面形貌, 并以结晶紫为探针分子测量了金核银壳纳米粒子薄膜的表面增强拉曼光谱(SERS). 结果表明, 金纳米粒子薄膜的分布、银增强剂反应时间的长短对金核银壳纳米粒子薄膜的形成均有重要影响. 制备过程中, 可以通过控制反应条件获得一定粒径的、具有良好表面增强拉曼散射活性的金核银壳纳米粒子薄膜.     

Electroresponsive Structurally Colored Materials: A Combination of Structural and Electrochromic Effects

Electroresponsive structurally colored materials composed of ordered arrays of polyaniline@poly(methyl methacrylate) (PANI@PMMA) core–shell nanoparticles have been successfully prepared. The core–shell nanoparticles were synthesized by deposition of PANI shells on the surfaces of the PMMA cores by the oxidative polymerization of anilinium chloride. Ordered arrays were then fabricated by using the fluidic cell method. Because the ordered arrays and the PANI shells generate structural and electrochromic colors, respectively, these core–shell colloidal crystals exhibited colors resulting from the combined effects of these materials. The crystal colors depended greatly on the size of PANI@PMMA particles and could also be varied by the application of a voltage. The electrochromic colors of these arrays were found to be quite different from those exhibited by pure PANI films prepared by electrochemical oxidation.