Nonaqueous synthesis and characterization of capped α-Fe2O3 nanoparticles from iron(III) hydroxy-oleate precursor

The synthesis of capped α-Fe₂O₃ nanoparticles from thermal treatment of iron (III) hydroxy-oleate in boiling organic solvents around 250 °C with retention of the integrity of the oleate units during the reaction process is reported. The formation of capped iron oxide particles is accomplished under aerobic conditions while the solvents used in the synthesis have strong influence on the nature and morphology of nanoparticles. These nanoparticles are studied by means of X-ray powder diffraction, IR and XPS while the morphology and particle size of nanocrystals are evaluated using SEM and TEM analysis suggesting the formation of monocrystalline α-Fe₂O₃ particles having cubical and spherical morphologies with sizes ranging from 20 to 30 nm. This organophilic material with oleate capping around the surfaces can be readily dispersed in organic solvents thus forming organosols. These organosols exhibit band-edge emission photoluminescence band both in toluene as well as in solid state while FT-IR analysis reveals formation oleate capped nanoparticles The XPS data indicate ferric state having doublet from Fe 2p_3/2 and Fe 2p_1/2 core-level electrons.     

Hyphenated analytical techniques for multidimensional characterisation of submicron particles: a review

The stakes concerning the characterisation of particles ranged in the size from 1 to 1000 nm, namely submicron particles, are today more and more important. Because of the variety of particles even inside a given sample in terms of dimension, mass, charge or chemical composition a characterisation as complete as possible is needed. The possibility of obtaining a multidimensional information by relevant analytical methods is then of the greatest interest. One very interesting strategy consists in using hyphenated techniques, which are intrinsically capable to provide rapidly and accurately such information. This paper summarises the different hyphenated techniques that can be used to characterise submicron particles and is focussed on their main applications to illustrate their current and potential uses. In order to have a relevant overview various on-line separation techniques are considered in a comparative way. In the same way various on-line detectors are then presented. Finally the concepts of multidetection and multidimensional analysis are discussed and their interest showed through different typical examples of hyphenated techniques illustrating submicron particle characterisation in fields of applications such as environmental and nanomaterial sciences.     

六角形氧化锌超晶格粒子的控制制备

本文通过蒸发微乳液体系中的溶剂得到了六角形的氧化锌亚微米粒子，其具有超晶格结构。所得产物用红外(FT-IR)和透射电镜(TEM)进行了表征，并进行了热重分析(TGA)。通过监测反应过程，研究了该粒子的形成机制。实验观察到约7nm的纳米氧化锌粒子聚集成亚微米的球形超晶格粒子，该球形粒子随溶剂蒸发进行了自组装，并由于界面相互作用转换成六角形的超晶格粒子。     

液化膜对胶体悬浮液粘度的影响

Viscosity is one of the most important properties of colloids in mixing, transportation, stabilization, energy consumption, and so on. According to Einstein‘s viscosity equation, the viscosity of a colloidal dispersion increases with the increase of particle concentration. And the equation can be applicable to all micro-particle dispersions, because the effect of solvation films coated on particles can be neglectable in that case. But with the decrease of particle size to nano-scale, the formation of solvation films on nano-particles can greatly affect the viscosity of a dispersion, and Einstein‘s equation may not be applicable to this case. In this work, one kind of micro-size silica particle and two kinds of nano-size silica particles were used to investigate the effect of solvation films on dispersion viscosity, dispersed in water and ethyl alcohol solvents, respectively. The results of theoretical calculation and experimental investigation show that the increase of viscosity is contributed from solvation films by more than 95 percent for nano-particle dispersions, while less than 10 percent for micro-particle dispersions.     

Synthesis of monodisperse fluorescent core-shell silica particles using a modified Stober method for imaging individual particles in dense colloidal suspensions

Core-shell silica particles, with a diameter of 1.5 mum, containing a dye fluorescein isothiocyanate (FITC), are synthesized by the hydrolysis and condensation of tetraethylorthosilicate (TEOS). Sodium dodecyl sulfate (SDS) is added to synthesize fluorescent core particles with the diameter of approximately 1 mum. In the addition of SDS, the surface charge reduced by counterions (Na+) of the surfactant leads to a higher degree of aggregation of the primary particles and the formation of larger secondary particles. The particle growth kinetics confirms the aggregation growth model for the synthesis of monodisperse silica particles, and also shows the dependence of final particle size on colloidal stability resulting from the addition of SDS. Light and X-ray scattering data reveal that the final particles have compactly packed structures with smooth surfaces. The seeded growth technique is then used to form a silica shell layer on the fluorescent core. The added amount of water and NH4OH has significant effects on shell formation. Finally, the final core-shell silica particles are modified by chemisorption of octadecanol at the surface to be dispersed in organic solvents. Octadecyl-coated silica particles are sterically stabilized in silica index-matching solvents such as chloroform and hexadecane to directly image separate particles using confocal microscopy. In chloroform, the organophilic silica particles disperse well, whereas in hexadecane they form a volume-filling gel structure at room temperature.     

聚合物粒子在生物化学与生物医学中的应用

就亚微米和单粒径两种新型的聚合物粒子在生物化学与生物医学如免疫分析、药物载体、真核细胞、原核细胞及生物大分子产品等的分离等领域中的最新应用进行了综述。     

Preparation of fluorescent particles with long excitation and emission wavelengths dispersible in organic solvents

We introduce a fast and simple one-step method, a variation of the methods of Barrett and Campbell and Bartlett, to synthesize monodisperse fluorescent particles that can be dispersed in organic solvents and have long excitation (649 nm) and emission wavelengths (679 nm). A lipophilic fluorescent dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine perchlorate, is directly incorporated into PMMA particles through dispersion polymerization. A poly(hydroxystearic acid) graft (poly) methyl methacrylate (MM) and methacrylic acid (MA) copolymer is used as a stabilizer to prevent the particles from aggregating and flocculating in the nonaqueous solvents. The fluorescent PMMA particles are very uniform in size, bleach at very low rate, and behave like hard spheres in their ordering on substrates. One important achievement in our synthesis protocol is that we are able to produce particles of a desired size by choosing the composition of the reactants according to a predetermined relationship between particle size and composition of reactants. In addition, the effects of fluorescent dye and polar solvent (ethanol) on the formation and size of particles are discussed.     

Preparation of micron-sized aromatic polyamide particles using ultrasonic irradiation

Aromatic polyamide particles were prepared by reacting p-phthalyl chloride and 4,4′-diaminodiphenyl ether in an acetone solution with a high water content, using a precipitation polymerization method with ultrasonic irradiation. The average particle diameter was ca. 712 nm, and the particles were porous and spherical with a narrow size distribution. They showed a high degree of crystallinity and excellent thermal stability. The morphology and the thermal decomposition temperature of the submicron particles were found to depend strongly on the volume of water added to the reaction system. In this polymerization method, the addition of water was essential for the formation of spherical particles. The simultaneous mixing process resulted in the formation of particles with a narrow size distribution, and the use of ultrasonic irradiation was effective in reducing particle size.     

Effects of solvent on TEOS hydrolysis kinetics and silica particle size under basic conditions

In-situ liquid-state ²⁹Si nuclear magnetic resonance was used to investigate the temporal concentration changes during ammonia-catalyzed initial hydrolysis of tetraethyl orthosilicate in different solvents (methanol, ethanol, n-propanol, iso-propanol and n-butanol). Dynamic light scattering was employed to monitor simultaneous changes in the average diameter of silica particles and atomic force microscopy was used to image the particles within this time frame. Solvent effects on initial hydrolysis kinetics, size and polydispersity of silica particles were discussed in terms of polarity and hydrogen-bonding characteristics of the solvents. Initial hydrolysis rate and average particle size increased with molecular weight of the primary alcohols. In comparison, lower hydrolysis rate and larger particle size were obtained in the secondary alcohol. Exceptionally, reactions in methanol exhibited the highest hydrolysis rate and the smallest particle size. Ultimately, our investigation elaborated, and hence confirmed, the influences of chemical structure and nature of the solvent on the formation and growth of the silica particles under applied conditions.     

Fractionated crystallization of polypropylene droplets produced by nanolayer breakup

Layer‐multiplying coextrusion was used to fabricate assemblies of 257 layers, in which polypropylene (PP) nanolayers alternated with thicker polystyrene (PS) layers. The PP layer thickness was varied from 12 to 200 nm. When the assembly was heated into the melt, interfacial instability‐driven breakup of the thin PP layers produced a dispersion of PP particles in a PS matrix. Particle size analysis indicated that breakup of PP microlayers produced a bimodal particle size distribution. A population of submicron particles formed because of the Rayleigh instability, and a second population of large particles formed by relaxation. Breakup of 12‐nm layers resulted in primarily submicron particles. The fraction of PP as submicron particles dropped dramatically as the layer thickness increased to 40 nm. The particle dispersion was characterized by thermal analysis and wide angle X‐ray diffraction. Fractionated crystallization gave rise to four crystallization exotherms at 40, 60, 85, and 100 °C. The exotherm at 40 °C was identified with homogeneous nucleation of the submicron particles in the smectic form. Exotherms at higher temperatures represented fractionated crystallization of the large micron‐sized particles in the PP α‐form. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1138–1151, 2007     

Assessment of submicron particle zeta potential in simple electrokinetic microdevices

The present communication illustrates the use of simple electrokinetic devices for the assessment of the zeta potential of submicron polystyrene particles. A combination of manual and automatic particle tracking was employed. This approach allows for characterizing particles in the same conditions and devices in which they can be separated, e.g. dielectrophoretic separations; making the resulting data readily applicable.     

Mechanism of the growth of monodispersed spherical silica particles to the submicron size

Summary Monodispersed spherical submicron silica particles were obtained by the precipitation of soluble silica on the surface of preliminary obtained smaller particles. Silica was added into the system at low concentrations to prevent both its polymerization in the solution and the formation of new particles. The kinetics of the particle growth is controlled by the diffusion of soluble silica through the double diffusion layer.     

Precipitation and Condensation of Organic Particles

The precipitation and condensation of submicron organic particles are reviewed. The importance of physical state effects is discussed, and the role of compartmentalization in controlling particle size is introduced. The thermodynamic driving forces for precipitation and phase transformation are briefly reviewed. The use of emulsification as a primary step in producing small particle dispersions is described and illustrated with photographic and pharmaceutical applications. Precipitation driven by solvent shifting is illustrated and applications in preparing organic–inorganic composites and protein coacervation are described. Miscible solvent–nonsolvent induced precipitation is outlined, and followed by related applications using supercritical fluid technology. The special case of solvent shifting, pH shifting, is reviewed at length and illustrated to be effective for preparing nanoparticles of organics having weak acid functional groups. The first applications of organic particle precipitation in reverse microemulsion systems are described. The applicability of gas condensation methods is illustrated. Exciting new applications of precipitation in submicron hollow spheres and dye entrapment in submicron polymer gel networks are discussed.     

Particle Analysis by SEM/EDXS and Specimen Damage

 Quantitative analysis of particles, especially environmental particles in the submicron region, is hampered mainly by radiation damage. It can already be observed for probe currents smaller than 1 nA and analysis times of 10 seconds. The main reason for radiation damage is the storage of thermal energy in the particle, until the melting temperature is reached, and the subsequent loss of one or more of the elements of the respective material, e.g. SO_x in K₂SO₄. The lower the melting point, the more severe the specimen damage. The amount of specimen damage can vary substantially even for particles of the same size and composition. Specimen damage on inorganic materials can be observed for energies as low as 1 keV. Thus radiation damage is the greatest obstacle to accurate quantitative analysis for particles in the submicron region, even for analysis times as low as those used in automated particle analysis by CCSEM/EDXS.     

单分散二氧化硅球形颗粒的制备与形成机理

在醇水混合溶剂中以氨作催化剂，正硅酸乙酯为硅源，通过溶胶—凝胶工艺制 备单分散二氧化硅球形颗粒，通过透视电镜进行研究各种反应条件如溶剂类型、氨 和水的浓度、水解温度等对二氧化硅的颗粒大小和形貌的影响．结果显示：以甲醇 和乙醇为溶剂可以形成单分散的二氧化硅球形颗粒，以丙醇和丁醇为溶剂，二氧化 硅球形颗粒容易聚集；在其它条件不变的情况下，球形颗粒的粒径随水和硅源的浓 度增加而增大；而且水解温度的升高，生成的颗粒粒径也逐渐增大，仔细研究和讨 论了二氧化硅颗粒在不同反应条件下的形成机理．     

Ozonolysis of mixed oleic acid/n-docosane particles: the roles of phase, morphology, and metastable states

The reaction kinetics of ozone with oleic acid (OA) in submicron particles containing n-docosane has been studied using aerosol CIMS (chemical ionization mass spectrometry) to monitor changes in particle composition. Internally mixed particles with X(OA) > 0.72 were found to exist as supercooled droplets when cooled to room temperature. Partial reaction of the oleic acid was seen to completely inhibit further reaction and was attributed to the formation of a metastable solid rotator phase of the n-docosane at the surface. This reaction-induced phase change is believed to prevent further reaction by slowing ozone diffusion into the particle. When these particles were cooled to 0 degrees C before reaction, they reacted to a further extent and did not demonstrate such an inhibition. This shift in reactivity upon cooling is attributed to the formation of the thermodynamically stable form of n-docosane, the triclinic solid. This transition was accompanied by an increase in the n-docosane density, which led to the development of "cracks" through which ozone can diffuse into the particle. The aerosol with X(OA) < 0.72 consisted of an external mixture of particles containing n-docosane in either the rotator or the triclinic solid phase because of the stochastic nature of the rotator --> triclinic transition. The reactivity of the oleic acid was seen to increase with increasing n-docosane content as a larger fraction of the particles underwent the rotator --> triclinic transition and therefore contained cracks at the surface. These findings demonstrate the importance of transient, metastable phases in determining particle morphology and how such morphological changes can influence rates of reactions in organic aerosols.     

Gram-scale synthesis of monodisperse gold colloids by the solvated metal atom dispersion method and digestive ripening and their organization into two- and three-dimensional structures

We describe a synthetic procedure for preparation of large quantities of monodisperse thiol-stabilized gold colloids in toluene solution. The method is based on the solvated metal atom dispersion technique (SMAD), which is very suitable for preparation of large amounts of metal colloidal solutions, as well as of metal sulfide, metal oxide, and other types of dispersed compounds in different solvents. A combination of two different solvents like acetone and toluene is used for the preparation of the gold colloids. The necessity of initially carrying out the SMAD reaction in acetone comes from its high degree of solvation of gold particles. Acetone acts as a preliminary stabilizing agent. After its removal from the system, the particles are stabilized by dodecanethiol molecules, which enable their very good dispersion in toluene solution. A digestive ripening procedure is carried out with the gold-toluene colloid, and for this purpose pure toluene as solvent is necessary. This has a dramatic effect on the narrowing of particle size distribution and almost monodisperse colloids are obtained (some discussion of the probable mechanism of this remarkable digestive ripening step is given). These colloidal solutions have a great tendency to organize in two- and three-dimensional structures (nanocrystal superlattices, NCSs). We believe that this procedure provides a real opportunity to synthesize large amounts of gold nanocrystals as well as NCSs.     

Fluorescent organosilica micro- and nanoparticles with controllable size

This paper reports on the synthesis of uniformly dye-doped organosilica particles with narrow size distribution. The particle size can be controlled from tenths of nanometers up to several micrometers, whilst still maintaining monodispersity. Microparticles were observed to swell in various solvents up to approximately 2.5 times their original volume, suggesting the presence of a gel-like internal structure. As shown by confocal microscopy, this morphological control of particle swelling has important implications for the encoding of the nano/micro particles with organic dyes, such as rhodamine B isothiocyanate. Swelling allows the dye to penetrate the organosilica matrix and produce uniformly dye-doped nano- and microparticles. Finally, we suggest a coagulation model for the particle formation which significantly differs from conventional St?ber synthesis.     

Modified polymer substrates for the formation of submicron particle ensembles from colloidal solution

Methods for targeted regulation of the surface properties of polymer film materials (substrates) by fluorination and sulfonation have been considered. It has been shown by the examples of polyethylene, polypropylene, and poly(ethylene terephthalate) films that these methods can be used for the production of polymer films with controlled values of water contact angle from 20° to 88°, adhesion force from 23 to 141 rel. units, and surface roughness parameter R_a from 35 to 382 nm. This set of substrates may be used to optimize the methods for the formation of structured functional polymer surfaces. In particular, the regularities of the formation of solid deposits of colloidal submicron particles during evaporation of droplets of their solutions have been shown to vary with variations in substrate characteristics.     

Sol-Gel and Ultrafine Particle Formation via Dielectric Tuning of Inorganic Salt-Alcohol-Water Solutions

Under some conditions, inorganic salts can be as good precursors for sol-gel-type processing as those obtained from expensive metalloorganic precursors such as alkoxides. In this work, the formation of monodispersed hydrous zirconia microsphere particles (particularly nanosized) and gels was achieved in solutions of zirconyl chloride dissolved in alcohol-water mixed solvents. The dielectric property of the mixed alcohol-water solvent directly affects the nucleation and growth of zirconia clusters/particles in homogeneous solutions. A lower dielectric constant of mixed solvent corresponds to a lower solubility of inorganic solute and, thus, a shorter induction period for nucleation as well as higher solid particle growth kinetics. Dynamic light scattering (DLS) was used to monitor the homogeneous nucleation and growth processes, while final particles and gels were studied by scanning electron microscopy (SEM) and high-temperature X-ray diffraction (HTXRD). The sol-gel processes in the mixed solvent system can be adjusted using the processing parameters, including the initial inorganic salt concentration (C), alcohol/aqueous medium volume ratio of the mixed solution (RH), incubation temperature (T), incubation time (t), concentration of hydroxypropyl cellulose (HPC), and ammonia neutralization. Monodispersed submicron and nanoscale (<100 nm) zirconia microspheres/powders were successfully synthesized under conditions of high RH (5) and using HPC (molecular weight of 100,000, 2.0x10(-3) g/cm(3)) and ammonia neutralization. Initial salt concentration affects the particle size significantly. Gel materials were obtained under conditions of low RH (1.0). Microstructure and transparency of gels changed significantly from low (0.05 M) to high (0.2 M) concentration of the metal salt. We have also demonstrated that monodispersed particle production can be achieved not only at low temperatures (<100 degrees C) but also at room temperature using an inorganic salt precursor. Copyright 2000 Academic Press.