Synthesis of micrometer-sized silica-stabilized polystyrene latex particles

Micrometer-sized silica-stabilized polystyrene latexes have been readily prepared by alcoholic dispersion polymerization using a 13 or 22 nm commercial alcoholic silica sol as the sole stabilizing agent. These resulting surfactant-free polystyrene particles have relatively narrow particle size distributions and contain surprisingly low levels of silica (相似文献   

Synthesis of vinyl polymer-silica colloidal nanocomposites prepared using commercial alcoholic silica sols

The surfactant-free synthesis of vinyl polymer-silica nanocomposite particles has been achieved in aqueous alcoholic media at ambient temperature in the absence of auxiliary comonomers. Styrene, methyl methacrylate, methyl acrylate, n-butyl acrylate, and 2-hydroxypropyl methacrylate were homopolymerized in turn in the presence of three commercially available ultrafine alcoholic silica sols. Stable colloidal dispersions with reasonably narrow size distributions were obtained, with silica contents of up to 58% by mass indicated by thermogravimetric analysis. Particle size distributions were assessed using both dynamic light scattering and disk centrifuge photosedimentometry. The former technique indicated that the particle size increased for the first 1-2 h at 25 degrees C and thereafter remained constant. Particle morphologies were studied using electron microscopy. Most of the colloidal nanocomposites comprised approximately spherical particles with relatively narrow size distributions, but in some cases more polydisperse or nonspherical particles were obtained. Selected acrylate-based nanocomposites were examined in terms of their film formation behavior. Scanning electron microscopy studies indicated relatively smooth films were obtained on drying at 20 degrees C, with complete loss of the original particle morphology. The optical clarity of solution-cast 10 microm nanocomposite films was assessed using visible absorption spectrophotometry, with 93-98% transmission being obtained from 400 to 800 nm; the effect of long-term immersion of such films in aqueous solutions was also examined. X-ray photoelectron spectroscopy studies indicated that the surface compositions of these nanocomposite particles are invariably silica-rich, which is consistent with their long-term colloidal stability and also with aqueous electrophoresis measurements. FT-IR studies suggested that in the case of the poly(methyl methacrylate)-silica nanocomposite particles, the carbonyl ester groups in the polymer are hydrogen-bonded to the surface silanol groups. According to differential scanning calorimetry studies, the glass transition temperatures of several poly(methyl methacrylate)-silica and polystyrene-silica nanocomposites can be either higher or lower than those of the corresponding homopolymers, depending on the nature of the silica sol.     

Efficient synthesis of poly(2-vinylpyridine)-silica colloidal nanocomposite particles using a cationic azo initiator

Colloidal poly(2-vinylpyridine)-silica nanocomposite particles can be efficiently prepared by emulsion polymerization at 60 degrees C using a commercial 20 nm aqueous silica sol as the sole stabilizing agent. Unlike previously reported colloidal nanocomposite syntheses, transmission electron microscopy studies indicate very high silica aggregation efficiencies (88-99%). The key to success is simply the selection of a suitable cationic azo initiator. In contrast, the use of an anionic persulfate initiator leads to substantial contamination of the nanocomposite particles with excess silica sol. The cationic azo initiator is electrostatically adsorbed onto the anionic silica sol at submonolayer coverage, which suggests that surface polymerization may be important for successful nanocomposite formation. Moreover, the 2-vinylpyridine can be partially replaced with either styrene or methacrylic comonomers to produce a range of copolymer-silica nanocomposite particles. The poly(2-vinylpyridine)-silica nanocomposite particles have a well-defined core-shell morphology, with poly(2-vinylpyridine) cores and silica shells; mean diameters typically vary from 180 to 220 nm, and mean silica contents range from 27 to 35% by mass.     

Correcting for a density distribution: particle size analysis of core-shell nanocomposite particles using disk centrifuge photosedimentometry

Many types of colloidal particles possess a core-shell morphology. In this Article, we show that, if the core and shell densities differ, this morphology leads to an inherent density distribution for particles of finite polydispersity. If the shell is denser than the core, this density distribution implies an artificial narrowing of the particle size distribution as determined by disk centrifuge photosedimentometry (DCP). In the specific case of polystyrene/silica nanocomposite particles, which consist of a polystyrene core coated with a monolayer shell of silica nanoparticles, we demonstrate that the particle density distribution can be determined by analytical ultracentrifugation and introduce a mathematical method to account for this density distribution by reanalyzing the raw DCP data. Using the mean silica packing density calculated from small-angle X-ray scattering, the real particle density can be calculated for each data point. The corrected DCP particle size distribution is both broader and more consistent with particle size distributions reported for the same polystyrene/silica nanocomposite sample using other sizing techniques, such as electron microscopy, laser light diffraction, and dynamic light scattering. Artifactual narrowing of the size distribution is also likely to occur for many other polymer/inorganic nanocomposite particles comprising a low-density core of variable dimensions coated with a high-density shell of constant thickness, or for core-shell latexes where the shell is continuous rather than particulate in nature.     

All-acrylic film-forming colloidal polymer/silica nanocomposite particles prepared by aqueous emulsion polymerization

The efficient synthesis of all-acrylic, film-forming, core-shell colloidal nanocomposite particles via in situ aqueous emulsion copolymerization of methyl methacrylate with n-butyl acrylate in the presence of a glycerol-functionalized ultrafine silica sol using a cationic azo initiator at 60 °C is reported. It is shown that relatively monodisperse nanocomposite particles can be produced with typical mean weight-average diameters of 140-330 nm and silica contents of up to 39 wt %. The importance of surface functionalization of the silica sol is highlighted, and it is demonstrated that systematic variation of parameters such as the initial silica sol concentration and initiator concentration affect both the mean particle diameter and the silica aggregation efficiency. The nanocomposite morphology comprises a copolymer core and a particulate silica shell, as determined by aqueous electrophoresis, X-ray photoelectron spectroscopy, and electron microscopy. Moreover, it is shown that films cast from n-butyl acrylate-rich copolymer/silica nanocomposite dispersions are significantly more transparent than those prepared from the poly(styrene-co-n-butyl acrylate)/silica nanocomposite particles reported previously. In the case of the aqueous emulsion homopolymerization of methyl methacrylate in the presence of ultrafine silica, a particle formation mechanism is proposed to account for the various experimental observations made when periodically sampling such nanocomposite syntheses at intermediate comonomer conversions.     

In situ small-angle X-ray scattering studies during the formation of polymer/silica nanocomposite particles in aqueous solution

This study is focused on the formation of polymer/silica nanocomposite particles prepared by the surfactant-free aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) in the presence of 19 nm glycerol-functionalized aqueous silica nanoparticles using a cationic azo initiator at 60 °C. The TFEMA polymerization kinetics are monitored using ¹H NMR spectroscopy, while postmortem TEM analysis confirms that the final nanocomposite particles possess a well-defined core–shell morphology. Time-resolved small-angle X-ray scattering (SAXS) is used in conjunction with a stirrable reaction cell to monitor the evolution of the nanocomposite particle diameter, mean silica shell thickness, mean number of silica nanoparticles within the shell, silica aggregation efficiency and packing density during the TFEMA polymerization. Nucleation occurs after 10–15 min and the nascent particles quickly become swollen with TFEMA monomer, which leads to a relatively fast rate of polymerization. Additional surface area is created as these initial particles grow and anionic silica nanoparticles adsorb at the particle surface to maintain a relatively high surface coverage and hence ensure colloidal stability. At high TFEMA conversion, a contiguous silica shell is formed and essentially no further adsorption of silica nanoparticles occurs. A population balance model is introduced into the SAXS model to account for the gradual incorporation of the silica nanoparticles within the nanocomposite particles. The final PTFEMA/silica nanocomposite particles are obtained at 96% TFEMA conversion after 140 min, have a volume-average diameter of 216 ± 9 nm and contain approximately 274 silica nanoparticles within their outer shells; a silica aggregation efficiency of 75% can be achieved for such formulations.

SAXS is used to study the formation of polymer/silica nanocomposite particles prepared by surfactant-free aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate in the presence of silica nanoparticles using a azo initiator at 60 °C.     

草莓型SiO2/PMMA纳米复合微球的制备

在纳米二氧化硅水分散体系中,借助于碱性辅助单体1-乙烯基咪唑(1-VID)与未改性纳米二氧化硅表面羟基之间的酸-碱作用,通过1-VID与甲基丙烯酸甲酯(MMA)的自由基共聚合,制备了草莓型的SiO2/PMMA复合微球.整个反应过程中,纳米二氧化硅无需表面处理,体系中无需另外加入乳化剂或助乳化剂,微球表面吸附的纳米二氧化硅对颗粒起稳定作用.用动态光散射粒度分布仪测得复合微球粒径在120-330nm之间,热重分析结果表明,复合微球中二氧化硅含量介于15%-20%之间.透射电镜和扫描电镜显示所得复合微球具有草莓型结构,二氧化硅富集在表面.     

草莓型PMMA/SiO2有机-无机复合微球的合成与表征

在纳米二氧化硅水分散介质中,借助于正离子单体甲基丙烯酰氧乙基三甲基氯化铵(MTC)与未改性纳米二氧化硅颗粒之间的电荷作用,通过MTC与甲基丙烯酸甲酯(MMA)的自由基共聚合,制备了草莓型的PMMA/SiO2复合微球.整个制备反应过程中,纳米二氧化硅无需表面处理,体系中无需另外加入乳化剂或助乳化剂,微球表面吸附的纳米二氧化硅对颗粒起稳定作用.详细讨论了纳米二氧化硅初始添加量、MTC浓度对复合微球的平均粒径、复合微球中二氧化硅含量及微球形态的影响.动态光散射粒度分布仪(DLS)测得复合微球粒径在180~300 nm之间,热重分析(TGA)表明复合微球中二氧化硅含量介于16.4%~40.8%之间.透射电镜(TEM)显示所得复合微球具有草莓型结构,二氧化硅于表面富集.     

Preparation of raspberry-like PMMA/SiO2 nanocomposite particles

Water-borne raspberry-like PMMA/SiO₂ nanocom-posite particles were prepared via free radical copolymerization of methyl methacrylate (MMA) with 1-vinylimidazole (1-VID) in the presence of ultrafine aqueous silica sols. The acid-base interaction between hydroxyl groups (acidic) of silica surfaces and amino groups (basic) of 1-VID was strong enough for promoting the formation of long-standing stable PMMA/SiO₂ nanocomposite particles when 10 mol% or more 1-VID as auxiliary monomer was used. The average particle sizes and the silica contents of the nanocomposite particles were in the ranges from 120–330 nm and 15%–20%, respectively. TEM and SEM observations indicated a raspberry-like morphology of the obtained nanocomposite particles. __________ Translated from Chemical Journal of Chinese Universities, 2005, 26(7) (in Chinese)     

非离子乳化剂细乳液聚合制备草莓型PSt/SiO2纳米复合微球

通过细乳液聚合,使用非离子乳化体系辛基酚聚氧乙烯醚(CA-897),在纳米二氧化硅水分散介质中,以1-乙烯基咪唑(1-VID)作为辅助单体制备了苯乙烯为核,纳米二氧化硅为壳的草莓型PSt/SiO2有机-无机复合微球.实验范围内得到的复合微球的平均粒径和最终SiO2含量分别介于140～180 nm和19 wt%-31wt...     

Anionic surfactant for silica-coated polystyrene composite microspheres prepared with miniemulsion polymerization

Raspberry-like composite microspheres with polystyrene (PS) cores and silica shell were prepared through miniemulsion polymerization by using the anionic sodium dodecyl sulfate (SDS) as a surfactant and 1-vinylimidazole (1-VID) as an auxiliary monomer. The strong acid–base interaction between acidic hydroxyl groups of silica surfaces and basic amino groups of 1-VID promote the formation of long-term stable PS/SiO₂ nanocomposite microspheres. Transmission electron microscopy TEM studies indicated that the acid–base interaction between silica nanoparticles and auxiliary monomer was strong enough for the formation of colloidally stable composite microspheres, which have raspberry-like morphology. Influences of several synthetic parameters, such as initial silica amount, the amount of auxiliary monomer 1-VID, and SDS concentration on the polymerization stability, diameters, and morphology of the composite microspheres were studied. A tentative mechanism of the formation of nanocomposite particles was proposed.     

Characterization of the nanomorphology of polymer-silica colloidal nanocomposites using electron spectroscopy imaging

The internal nanomorphologies of two types of vinyl polymer-silica colloidal nanocomposites were assessed using electron spectroscopy imaging (ESI). This technique enables the spatial location and concentration of the ultrafine silica sol within the nanocomposite particles to be determined. The ESI data confirmed that the ultrafine silica sol was distributed uniformly throughout the poly(4-vinylpyridine)/silica nanocomposite particles, which is consistent with the "currant bun" morphology previously used to describe this system. In contrast, the polystyrene/silica particles had a pronounced "core-shell" morphology, with the silica sol forming a well-defined monolayer surrounding the nanocomposite cores. Thus these ESI results provide direct verification of the two types of nanocomposite morphologies that were previously only inferred on the basis of X-ray photoelectron spectroscopy and aqueous electrophoresis studies. Moreover, ESI also allows the unambiguous identification of a minor population of polystyrene/silica nanocomposite particles that are not encapsulated by silica shells. The existence of this second morphology was hitherto unsuspected, but it is understandable given the conditions employed to synthesize these nanocomposites. It appears that ESI is a powerful technique for the characterization of colloidal nanocomposite particles.     

Fabrication and characterization of raspberry-like PSt/SiO2 composite microspheres via miniemulsion polymerization

Raspberry-like composite microspheres with polystyrene (PSt) as cores and nanosilica particles as shell were prepared through miniemulsion polymerization by using the anionic sodium dodecyl sulfate (SDS) as surfactants and 2-(methacryloyl) ethyltrimethylammonium chloride (MTC) as auxiliary monomer. TEM indicated that the colloidally stable composite microspheres have the typical raspberry-like morphology. Zeta potential measurements confirmed that the positively charged MTC was located on the surface of the composite microspheres and had a drastic impact on the formation of the composite microspheres. The average particle sizes and the final silica contents of the composite microspheres could range from 150 to 250 nm and 10 to 40 wt%, respectively, depending upon the reaction conditions. The influences of some synthetic parameters, for instance, the initial silica amount, MTC amount and SDS concentration on the polymerization stability, diameters, silica contents and morphology of the composite microspheres were studied in detail.     

A facile strategy for controlling the self-assembly of nanocomposite particles based on colloidal steric stabilization theory

A heterocoagulation strategy based on colloidal steric stabilization theory has been developed, through which polystyrene (PS) and silica (SiO(2)) particles without any surface modification or functionalization self-assembled rapidly via solution to afford nanocomposite particles with raspberry-like morphology. The formation mechanism is fully studied on the basis of a thermodynamic analysis. The soluble stabilizer and the solvent quality are the main determining factors, which have a significant influence on this self-assembly process and the silica coverage of resultant composites. The relative size of PS to SiO(2) candidates also has the effect of control on the extent of self-assembly. Furthermore, this strategy can be applied to fabricate a broad range of composite materials, including PS/TiO(2), PS/AgI, as well as PS/PS composites.     

单分散SiO2/PS复合粒子的制备

聚合物包覆无机物的核一壳结构复合粒子研究长期以来受到关注,源于其应用广泛．根据表面性质要求对无机相或者有机相表面进行功能化,可使得到的复合粒子与不同的应用体系相匹配．这类聚合物包覆无机物的有机／无机复合粒子,已在光学器件、分离、药品、农业、涂料等很多领域有广泛和潜在应用．本文制备这类复合粒子用于石油工业模型催化剂和助剂．     

Fabrication of sub-micrometer-sized jingle bell-shaped hollow spheres from multilayered core-shell particles

Jingle bell-shaped hollow spheres were fabricated starting from multilayered particles composed of a silica core, a polystyrene inner shell, and a titania outer shell. Composite particles of silica core-polystyrene shell, synthesized by coating a 339-nm-sized silica core with a polystyrene shell of thickness 238 nm in emulsion polymerization, were used as core particles for a succeeding titania-coating. A sol-gel method was employed to form the titania outer shell with a thickness of 37 nm. The inner polystyrene shell in the multilayered particles was removed by immersing them in tetrahydrofuran. These successive procedures could produce jingle bell-shaped hollow spheres that contained a silica core in the titania shell.     

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     

Synthesis of SiO2/polystyrene nanocomposite particles via miniemulsion polymerization

The SiO(2)/polystyrene nanocomposite particles were synthesized through miniemulsion polymerization by using sodium lauryl sulfate surfactant (SLS), hexadecane costabilizer in the presence of silica particles coated with methacryloxy(propyl)trimethoxysilane. Core-shell or other interesting morphology composite particles were obtained depending on the size of the silica particles and the surfactant concentration employed. By adjusting these parameters, it was possible to control the size and morphology of the composite particles.     

Micelles of poly(styrene-b-2-vinylpyridine-b-ethylene oxide) with blended polystyrene core and their application to the synthesis of hollow silica nanospheres

Core-shell-corona (CSC) micelles of asymmetric triblock copolymer, poly(styrene-b-2-vinylpyridine-b-ethylene oxide) (PS-PVP-PEO), containing polystyrene homopolymer (homo-PS) in the core were successfully prepared in aqueous media. The influence of homo-PS contents over the formation of the micelles was investigated thoroughly by various techniques such as dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fluorescence spectroscopy. It was found that the size of the PS core of the micelle was increased by the addition of homo-PS as observed by DLS and TEM techniques. The SEM and TEM measurements confirm the spherical morphology of the micelles and enlargement of PS core over the addition of homo-PS. The increase in the PS core volume of the PS-PVP-PEO micelles is attributed to the insertion of homo-PS in the PS core. The micelles have also been demonstrated as facile soft templates for synthesis of hollow silica nanospheres. The average diameter of the spherical hollow particles could be tuned between 30.6 and 38.8 nm with cavity sizes ranging from 20.7 to 28.5 nm using tetramethoxysilane as silica precursors under mild acidic conditions. The facile synthesis of hollow silica using the CSC micelles with different homo-PS contents indicates that the hollow void size can be controlled within a range of several nanometers.     

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.