Photocurable pickering emulsion for colloidal particles with structural complexity

We prepared polymeric microparticles with coordinated patches using oil-in-water emulsion droplets which were stabilized by adsorbed colloidal polystyrene (PS) latex particles. The oil phase was photocurable ethoxylated trimethylolpropane triacrylate (ETPTA), and the particle-armored oil droplets were solidified by UV irradiation within a few seconds to produce ETPTA-PS composite microparticles without disturbing the structures. Large armored emulsion drops became raspberry-like particles, while small emulsion drops with a few anchored particles were transformed into colloidal clusters with well-coordinated patches. For high-molecular-weight PS particles with low chemical affinity to the ETPTA monomer, the morphology of the patchy particle was determined by the volume of the emulsion drop and the contact angle of the emulsion interface on the PS particle surface. Meanwhile, for low-molecular-weight PS particles with high affinity, the ETPTA monomers were likely to swell the adsorbed PS particles, and distinctive morphologies were induced during the shrinkage of emulsion drops and the phase separation of ETPTA from the swollen PS particles. In addition, colloidal particles with large open windows were produced by dissolving the PS particles from the patchy particles. We observed photoluminescent emission from the patchy particles in which dye molecules were dispersed in the ETPTA phase. Finally, we used Surface Evolver simulation to predict equilibrium structures of patchy particles and estimate surface energies which are essential to understand the underlying physics.     

In situ synthesis of polysaccharide nanoparticles via polyion complex of carboxymethyl cellulose and chitosan

Biocompatible polymer-magnetite hybrid nanoparticles were prepared by means of in situ synthesis of magnetite within polysaccharide hydrogel nanoparticles. Hydrogel nanoparticles were first fabricated by blending high-molecular-weight carboxymethyl cellulose as an anionic polymer, and low-molecular-weight chitosan as a cationic polymer to form polyion complexes (CC particles). These polyion complexes were then chemically crosslinked using genipin, a bio-based cross-linker, to form stable nanoparticles having a semi-IPN structure (CCG particles). Magnetite was lastly synthesized within CCG particles by the coprecipitation method to obtain polymer-magnetite hybrid nanoparticles (CCGM particles). The formations of CC, CCG and CCGM particles were mainly observed by transmittance, absorbance of genipin and TEM, respectively, and their hydrodynamic diameters and zeta-potentials were analyzed. It was confirmed that the hydrodynamic diameters and the zeta-potentials of these particles were significantly influenced by pH of the suspension, which was attributed to the charges of polymers. The diameters of CCGM particles were smaller than 200 nm at any pH conditions, suggesting the possibility to apply them as drug delivery carriers. CCGM particles exhibited the responsiveness to a magnetic field in addition to their high dispersion stability, indicating their potential to be utilized as a biomaterial for hyperthermia.     

Atomic Force Microscopy Study of Ultrafine Particles Prepared in Reverse Micelles

The imaging of ultrafine Au, Pd, CdS, and ZnS particles prepared in reverse micelles has been studied by atomic force microscopy (AFM). Mica substrates, derivatized with a monolayer of amine or thiol-terminated silanes, were used to immobilize the particles. The substrates were exposed to reverse micellar solutions containing the particles and were then immersed in appropriate solvent media to remove surfactants. This resulted in a partial coating of the surfaces by the particles. The particle size was estimated as the height of protrusion, shown on the AFM images. The size values for the Pd and CdS particles, thus obtained, were found to be almost identical to those obtained by transmission electron microscopy (TEM), whereas those for the Au and ZnS particles were larger than those obtained by TEM. Scanning electron microscopy showed that the Au particles tended to aggregate on the surfaces, while Pd particles were isolated from one another. Copyright 2000 Academic Press.     

Preparation of Tin Oxide-Based Metal Oxide Particles

Tin oxide-doped hybrid particles were prepared by a wet chemical process with organic-inorganic (phenyl/silica) hybrid particles in an alcoholic solution. The phenyl/silica hybrid particles, with a diameter of ca. 790 nm were used as a new support material for tin oxide (SnO₂) particles from tin(IV) chloride. The surface of the particles was modified via nitration of aromatic groups in the particles, to promote formation of the tin oxide coating on the particles. The thickness and surface morphology of the tin oxide layer coated on the nitrated-phenyl/silica hybrid particles could be controlled by varying the tin(IV) chloride concentration and reaction time. The size and morphology of the resultant particles were investigated with field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The particles obtained were also characterised by infrared (FTIR) and solid-state ¹³C magic angle spinning nuclear magnetic resonance (¹³C-CP/MAS NMR) spectroscopy. The effect of processing parameters on the crystallinity and structure of the doped hybrids were confirmed by X-ray diffraction (XRD) patterns.     

Interactions between chitosan-modified particles and mucin-coated surfaces

Lipid-based particles (Cubosome particles) were surface-modified by chitosan and the ratio between particles and chitosan was optimized to minimize the free chitosan concentration in the dispersion. The modified particles were characterized by electrophoretic measurements and the pH dependence of the zeta potential could be directly related to the protonation of chitosan. Interaction between the modified particles and mucin-coated silica surfaces were subsequently investigated in situ by ellipsometry to assess the mucoadhesive properties at physiologically relevant conditions. The result showed that a substantial amount of modified particles was adsorbed to mucin-coated silica surfaces at both pH 4 and pH 6, probably due to electrostatic interactions between amino groups in chitosan and negatively charged groups in mucin. Furthermore, the amount of bound particles decreased by less than 15% upon rinsing indicating relatively strong interactions. This investigation demonstrates that ellipsometry is a useful tool to study mucoadhesive properties of particles in the submicrometer range. Moreover, the novel chitosan-modified particles may be of interest for mucosal drug delivery applications.     

Control on size and adsorptive properties of spherical ferric phosphate particles

Ferric phosphate particles were prepared by aging a solution dissolving Fe(ClO4)(3) and H3PO(4) at 40-80 degrees C for 16 h in a Teflon-lined screw-capped Pyrex test tube. The spherical or agglomerated fine particles were only precipitated with an extremely fast rate of reaction. The spherical particles were only produced at a very narrow region in fairly low pH solutions. TEM observation revealed that these particles grew in spherical structure by aggregation of primary small particles. The size of spherical particles was decreased by increase in the solute concentration or raising the aging temperature. Therefore, the formation of spherical particles was explained by a polynuclear layer mechanism proposed by Nielsen. The uniform spherical particles produced are amorphous, but they were crystallized to FePO(4) after calcining above 600 degrees C. It was suggested that the voids between the primary particles within the secondary agglomerated particles constitute mesopores. The Fe/P molar ratio determined and weight loss in TG curves gave the chemical formulas of the particles as Fe(PO4)x(H2PO4)y.nH2O (x: 0.93-1.00, y: 0-0.22, n: 2.4-2.7). The amorphous spherical ferric phosphate particles showed a high selective adsorption of H2O by penetration of H2O molecules into ultramicropores, produced after outgassing pretreatment, of that size is smaller than N2 molecule. The more particles grew, the more adsorption selectivity of H(2)O became remarkable.     

Acetaminophen particle design using chitosan and a spray-drying technique

In this study matrices were prepared from particles of poorly water-soluble drugs such as acetaminophen (Act) to determine the drug release rate from these matrix particles. The matrix particles were prepared by incorporating drugs into chitosan powder (Cht, carrier) using a spray-drying method. The formation of composite particles was confirmed by scanning electron microscopic (SEM) analysis. The matrix particles prepared by spray-drying were spherical with a smooth surface. The crystallinity of acetaminophen in the composite particles was evaluated by powder X-ray diffraction and differential scanning calorimetry (DSC). The degree of crystallinity of acetaminophen in the matrix particles decreased with a reduction in the weight ratio of acetaminophen relative to the carrier. These results indicate that a solid dispersion of acetaminophen in chitosan forms matrix particles. The interaction between acetaminophen and chitosan was also investigated by FT-IR analysis. FT-IR spectroscopy of the acetaminophen solid dispersion suggested that the carbonyl group of acetaminophen and the amino group of chitosan formed a hydrogen bond. There were some differences at pH levels of 1.2 and 6.8 in the release of acetaminophen from the physical mixture compared to the matrix particles. At pH 1.2, the release from the matrix particles (Act : Cht=1 : 5) was more sustained than from the physical mixtures. The 70% release time, T70, of acetaminophen from the matrix particles (Act : Cht=1 : 5) increased in pH 1.2 fluid by about 9-fold and in pH 6.8 fluid by about 5-fold compared to crystalline acetaminophen. These results suggest that matrix particles prepared by spray-drying are useful as a sustained release preparation.     

Surface modification of crosslinked poly(styrene-divinyl benzene) micrometer-sized particles of narrow size distribution by ozonolysis

Micrometer-sized polystyrene template particles of narrow size distribution were prepared by dispersion polymerization of styrene in 2-methoxyethanol. Uniform micrometer-sized polystyrene/crosslinked poly(styrene-divinyl benzene) composite particles were formed by a single-step swelling process of the template particles with styrene, divinyl benzene and benzoyl peroxide, followed by polymerization at 70 degrees C. Uniform micrometer-sized crosslinked poly(styrene-divinyl benzene) particles of higher surface area were produced by dissolution of the template polystyrene part of the former composite particles with N,N-dimethylformamide. Hydroperoxide conjugated crosslinked poly(styrene-divinyl benzene) particles were produced by ozonolysis of these particles. The effect of ozonolysis conditions, such as exposure time and flow rate of the ozone, on the hydroperoxide conjugation to the crosslinked particles was also studied. Functionalization of the crosslinked poly(styrene-divinyl benzene) particles was performed by graft polymerization of vinylic monomers such as acrylonitrile and chloromethylstyrene on the hydroperoxide conjugated crosslinked particles. This was accomplished by raising the temperature (e.g., 70 degrees C) of deairated acetonitrile dispersions containing the hydroperoxide conjugated particles and the vinylic monomers. The influence of various polymerization parameters on the grafting yield, e.g., monomer concentration, conjugated hydroperoxide concentration, and temperature, was also elucidated.     

Influence of particle coating on dynamic mechanical behaviors of magnetorheological elastomers

In this paper, core-shell structured poly methyl methacrylate (PMMA) coated carbonyl iron (CI) particles were prepared to study the influence of particle coating on the dynamic properties of magnetorheological elastomers (MREs). The CI-PMMA composite particles were encapsulated via an emulsion polymerization method. Two MRE samples were prepared with CI-PMMA composite particles and CI particles, respectively. Their microstructure was observed by using a scanning electron microscope (SEM). Dynamic properties of these two samples under various strain and magnetic fields were measured with a dynamic mechanical analyzer (DMA). The experimental results indicate that the MRE sample with CI-PMMA composite particles has larger storage modulus, smaller loss factor and smaller Payne effect than that of the sample with only CI particles. The analysis indicates that the use of CI-PMMA particles would increase the bond strength between particles and matrix. These experimental results were also verified by the SEM images.     

Design and Synthesis of Transparent Poly （acrylonitrile-butadiene-styrene） and Relationship Between Its Phase Construction and Transparency

IntroductionABS resins have been widely applied to the field ofengineering materials because of their excellent me-chanical,electrical,physical,and chemical proper-ties.Typically,ABS resins comprise a rigid copolymermatrix-phase dispersed in a graft copol…     

聚硅氮烷包敷纳米铁磁粉PSZFe的合成及其雷达波吸收性能研究

金属磁性材料是一类很重要的雷达波吸收材料 ,而纳米铁磁粉是其中的姣姣者 ,具有质量轻、居里温度高、磁化强度高 (可以是铁氧体磁性材料的 2～ 3倍 ) [1,2 ] 、矫顽力大、雷达波吸收性能好和频带宽等优点[3 ] ;但由于其颗粒太细 ,暴露在空气中即被强烈氧化 ,实际应用很困难 ,对其进行包敷处理是一种很有效的抗氧化腐蚀方法 .聚硅氮烷(PSZ)做为纳米铁磁粉包敷层有很多优点 :包敷层所要求的化学和力学性能可以通过调整氯硅烷单体的比例以及反应条件而实现[4] ;包敷层具有高致密性、高疏水性 ,从而使潮气、水和氧气很难侵入 ;包敷层耐热性好…     

扫描探针显微技术研究聚苯乙烯单链颗粒的力学响应

首先通过极稀溶液滴膜的方法得到了聚苯乙烯的单链颗粒 .之后 ,采用稍浓溶液得到了既有单链聚苯乙烯颗粒又有多链 (上千根 )聚苯乙烯颗粒的样品 .力调制技术显示单链聚苯乙烯颗粒比多链聚苯乙烯颗粒软 ;另一方面 ,对多链聚苯乙烯颗粒和聚苯乙烯本体的纳米压印实验结果表明二者的模量是近似的 .因此 ,可以得出单链聚苯乙烯颗粒比本体聚苯乙烯软 ,这说明存在于聚苯乙烯单链颗粒中的分子链内的缠结点密度不如存在于本体中的分子链间的缠结点密度大     

Adsorption of styrene on micron-sized, monodisperse, cross-linked polymer particles in a snowman-shaped state by utilizing the dynamic swelling method

Polystyrene/styrene–divinylbenzene copolymer composite particles with different cross-linking densities were produced by seeded copolymerization for (styrene/divinylbenzene)-swollen polystyrene particles prepared by utilizing the dynamic swelling method (DSM) which was proposed by the authors in 1991. Using the cross-linked, composite particles as seeds, styrene-adsorbed (swollen) composite particles having snowman shapes were prepared by the DSM. With a decrease in the cross-linking density in the composite particles, the volume of the composite particle which was embedded in a spherical styrene phase in the snowman-shaped, styrene-adsorbed particle increased and the contact angle of the styrene phase on the composite particle decreased. In the DSM process, the absorption stage of styrene in the composite particles and the adsorption stage thereon were clearly observed. This suggests that the cross-linking density of the composite particles greatly affects the morphology of the snowman-shaped particles. Received: 13 December 2000 Accepted: 14 March 2001     

Pyramidal assemblies of colloidal particles by micromolding underneath top-gathering pillar arrays

Assemblies of colloidal particles are known to have special photonic and optical properties. Periodic pyramidal assemblies of SiO2 particles with diameters of 0.5 and 1 microm were fabricated using top-gathering pillar arrays as a new template. These top-gathering pillar arrays consisted of four pillars gathered at the top, and were fabricated by photolithography of an organic-inorganic hybrid material. The top-gathering units were obtained by controlling both the capillary and restoring forces. When a colloidal water suspension was spread on the template and the water was allowed to evaporate, the SiO2 particles were molded under the top-gathering pillars according to particle size, resulting in pyramidal assembly arrays of the particles. From in situ observation during the evaporation of water, it was found that the particles were molded underneath the top-gathering pillars by flux generated by the evaporation and by the capillary force among the particles.     

Effects of guest microparticles on the swelling behavior of polyacrylamide gels

We report the effects of guest particles on the swelling properties of bulk polyacrylamide gels. The guest particles were the spheres of poly(N‐isopropylacrylamide) gel with submicrometer diameter, which were synthesized by an emulsion‐polymerized reaction in water. Polyacrylamide gels were prepared by a free radical polymerization reaction, immobilizing the gel microparticles with different concentrations at gelation. The macroscopic swelling ratio of this hybrid gel in a cylindrical shape was measured as functions of temperature and acetone concentration. The presence of guest particles was found to strongly affect the swelling behavior in the bulk gels when the concentration of incorporated particles exceeded a threshold. The experimental results indicated that the macroscopic volume in response to the temperature change should be determined by the guest particles above the threshold. On the other hand, the hybrid gel could not evidently shrink by adding acetone when the concentration of guest particles exceeded the threshold. To make clear the distribution of guest particles in the bulk networks, the fractured surfaces of dried gels were imaged by tapping mode atomic force microscopy. The guest particles were found to aggregate in the bulk homogeneous networks to form microdomains with densely connected structure, which became larger with increasing particle concentration. The roles of bulk networks as well as guest particles on the swelling behavior of hybrid gels were qualitatively discussed on the basis of the incorporated structure of guest particles, depending on the concentration of guest particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1696–1704, 2005     

等规聚苯乙烯的单分子链及单链单晶的尺寸判据

将等规聚苯乙烯配成苯的稀溶液，在水面上逐滴扩散，制备得到等规聚苯乙烯的超细微粒，并将微粒在４４８．２Ｋ等温结晶．用透射电镜对非晶态和昌态的粒子进行研究．由电镜测量得到的等规聚苯乙烯的分子量及分子量分布与其ＧＰＣ表征值基本相符，证明我们所得到的超细微粒是单分子尺寸的．     

Distribution of macropores in silica particles prepared by using multiple emulsions

The distribution of macropores in silica particles prepared by the hydrolysis and condensation of TEOS in a hexane/water/decyl alcohol (O(1)/W/O(2)) multiple emulsion was investigated. To stabilize the emulsion structure, hydroxypropyl cellulose (HPC) was added into the O(2) phase and polyethylene glycol (PEG) was added into the water phase. Without HPC, the particles have an irregular shape and hardly have particulate forms. As the concentration of HPC increases, the shape of particles becomes more and more spherical and the size decreases. The size of silica particles was varied from 5 to 1 microm as the concentration of HPC increased from 0.5 to 0.7 wt%. The number and size of the macropores in silica particles were affected by PEG polymer concentration. With the variation in the concentration of PEG, macropores in silica particles were located at the surface of or inside the particles. At high concentrations of PEG, the macropores in particles were located inside the particles, but at low concentrations of PEG the macropores were located at the surfaces of particles. Interestingly, the particles of dimpled surfaces were formed when the molar ratio of water to TEOS (R(w)) was 4.0 and the concentrations of PEG and HPC were 2.0 and 0.7 wt% respectively. The surface areas of dimpled silica particles and completely spherical particles, measured by the BET method, were 409 and 433 m(2)/g respectively.     

Monolayers of mono- and bidisperse spherical polymer particles at the air/water interface and Langmuir-Blodgett layers on solid substrates

Monodisperse spherical polymer particles with anionic and cationic shells were studied for their monolayer formation and compression behaviour on an aqueous subphase as a function of pH and salt (KCl) concentration. In addition, monolayers of monodisperse and bidisperse mixtures of 434 and 214 nm sized anionic particles were studied for their morphology by scanning electron microscopy (SEM). The anionic particles were prepared by soap-free emulsion polymerization of styrene and acrylic acid, and the cationic particles from styrene and 2-acryloxyethyl trimethylammonium chloride. Independent of the chemical nature of the shell, the particles formed monolayers at high salt or acid concentration in the subphase. However, at neutral pH and if no salt was present in the subphase only a part of the spheres formed monolayers, while the residual particles disappeared into the subphase. The origin of this behaviour is discussed in terms of ionization and electrostatic shielding of the polar groups.Compressed monolayers of monodisperse particles consisted of randomly oriented domains of up to 20 particles with small holes in between, the holes not exceeding two particle diameters in size. Films of bidisperse mixtures were highly disordered. If small particles were present in excess, they formed a fairly disordered monolayer and the large particles were situated on top or below this layer. If the number ratio of both sorts of particles approached unity, the texture became disordered and bi- and multilayered aggregates were observed.     

Size-controlled, one-pot synthesis, characterization, and biological applications of epoxy-organosilica particles possessing positive zeta potential

Epoxy-organosilica particles made from 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (EpoMS) as a single silica source were synthesized by means of a one-pot method. We evaluated three sets of synthesis conditions, including traditional Stober conditions and two variations. Although the traditional conditions did not afford EpoMS particles, the variations did. The size distributions of the particles were evaluated by means of transmission electron microscopy. The mean diameters and size distributions of the particles depended on the EpoMS concentration, and the best coefficient of variation for the size distribution was 5.9%. The surface of the particles had unique properties, such as a positive zeta potential. The particles bound strongly to proteins as well as to DNA. The particles made from EpoMS, allowing particles internally functionalized with fluorescent dye to be prepared by means of a one-pot synthesis. EpoMS particles doped and tuned with fluorescent dye showed strong fluorescence signals and distinct peaks on flow cytometry, and the fluorescent particles could be used to label cells. The labeled cells showed clear fluorescence under a fluorescence microscope, and electron microscopy showed many particles in the cytoplasm. This is the first report describing the synthesis of epoxy-organosilica particles with a positive zeta potential and describing differences in the characteristics of particle formations due to changes in synthesis conditions. We also discuss the advantages of EpoMS particles, as well as the potential biological applications of these particles.     

Silica- and alkoxysilane-coated ultrasmall superparamagnetic iron oxide particles: a promising tool to label cells for magnetic resonance imaging

In this study silica- and alkoxysilane-coated ultrasmall superparamagnetic iron oxide (USPIO) particles were synthesized, and their ability to label immortalized progenitor cells for magnetic resonance imaging (MRI) was compared. USPIO particles were synthesized by coprecipitation of ferric and ferrous salts. Subsequently, the particles were coated with silica, (3-aminopropyl)trimethoxysilane (APTMS), and [N-(2-aminoethyl)-3-aminopropyl]trimethoxysilane (AEAPTMS). The size of the USPIO particles was about 10 nm without a significant increase in diameter after coating. The highest T2 relaxivity was achieved for silica-coated USPIO particles, 339.80 +/- 0.22 s-1 mM-1, as compared with APTMS- and AEAPTMS-coated ones, reaching 134.40 +/- 0.01 and 84.79 +/- 0.02 s-1 mM-1, respectively. No toxic effects on the cells could be detected by trypan blue, TUNEL, and MTS assays. Uptake of USPIO particles was evaluated by Prussian blue staining, transmission electron microscopy, T2-MR relaxometry, and mass spectrometry. It was found that cell uptake of the different USPIO particles increased for longer incubation times and higher doses. Maximum cellular iron concentrations of 42.1 +/- 4.0 pg/cell (silica-coated USPIO particles), 37.1 +/- 3.5 pg/cell (APTMS-coated USPIO particles), and 32.7 +/- 4.0 pg/cell (AEAPTMS-coated USPIO particles) were achieved after incubation of the cells with USPIO particles at a dose of 3 micromol/mL for 6 h. The decrease of the T2 relaxation time of the cell pellets was most pronounced for cells incubated with silica-coated USPIO particles followed by APTMS- and AEAPTMS-coated particles, respectively. In gelatin gels even small clusters of labeled cells were detected by 1.5 T MRI, and significant changes in the T2 relaxation times of the gels were determined for 10000 labeled cells/mL for all particles. In summary, as compared with APTMS- and AEAPTMS-coated particles, silica-coated USPIO particles provide the highest T2 relaxivity and most effectively reduce the T2 relaxation time of immortalized progenitor cells after internalization. This suggests silica-coated USPIO particles are most suited for cell labeling approaches in MRI.