Seed Dispersion Polymerization to Micron-Size Monodisperse Polymer Particles

Abstract

Seed dispersion polymerization of methyl methacrylate (MMA) in the presence of monodisperse PMMA particles was carried out in an aqueous methanol using poly(methacrylic acid) stabilizer. The polymerization using 2. 5 μ. m-sized seed particles gave monodisperse PMMA particles in the diameter up to 4. 9 μm. The solvent composition and monomer concentration greatly affected the polymerization behavior. Under appropriate conditions, monodisperse PMMA particles in the diameter up to 8. 9 μ, m was prepared from 4. 6 μm-sized seed particles. The seed dispersion polymerization of styrene in the presence of the seed particles produced monodisperse PMMA-polystyrene particles in the micron range. The particles were supposed to have a structure consisting of PMMA-core and polystyrene-shell from ESCA analysis.     

The effect of the disperse composition of a titanium catalyst on the kinetic heterogeneity of isoprene polymerization centers

The kinetic heterogeneity of centers of isoprene polymerization on fractions of titanium catalyst particles is studied. It is found that the isoprene polymerization with a catalyst consisted of particles 0.03–0.14 μm in diameter involves centers of one type with low reactivity. On catalyst particles 0.15–4.50 μm in diameter, the active centers of polymerization of two types with high reactivity may be formed. The addition of modifiers, a reduced temperature of catalyst formation, and the hydrodynamic effect result in the appearance of a narrow fraction of particles 0.15–0.18 μm in diameter with one type of surface active center that generates high-molecular-mass cis-1,4-polyisoprene. The obtained results are in accordance with the concept of particles 0.15–4.50 μm in diameter as aggregates of the elementary crystallites of β-TiCl₃ connected via additional Al-Cl bonds to surface titanium atoms. At the same time, catalyst particles 0.03–0.14 μm in diameter are formed by the minimum number of elementary crystallites, where titanium atoms are bound to a smaller number of chlorine atoms.     

Emission efficiency for particulate forms of iron and aluminum in rain-water measured by inductively-coupled plasma atomic emission spectrometry

The bulk emission efficiency for particulate forms of iron and aluminum in rain-water was evaluated. The efficiencies for iron and aluminum were >80% for particles 0.4–1 μm in diameter and about 17% for particles >8 μm; relative standard deviations were <20%. A procedure is described by which the concentrations of particulate forms of iron and aluminum in rain-water are determined. Fluctuation of particles in rain-water during a rainfall event can be monitored in detail.     

Localization of glass particles in animal organs derived from cutting of glass ampoules before intravenous injections

Glass particles derived from the cutting of glass ampoules and suspended in parenteral solutions were introduced into mouse organs by intravenous injections in the tail vein. Organs were removed, thin sectioned, and plasma ashed on glass slides by means of glow-discharged oxygen to remove organic matrices which interfered with microscopic observation of glass particles. The ashed specimens were subsequently coated with a thin film of plasma-polymerized tetrafluoroethylene which suppressed the hygroscopicity of the specimens so that they became hydrophobic and at the same time permanently preserved the microstructures of the ashed specimens. Microscopic investigation of the glass particles retained in the ashed specimens supported size-dependent localization of the glass particles in different organs; i.e., large particles over 20 μm in diameter were mostly retained in the lung, while smaller particles around 5–10 μm in diameter were found in the liver and spleen, and occasionally in the kidney. A mesh-screen effect was therefore supposed along the route of blood circulation. No glass particle was found in the brain. Large numbers of extremely small glass particles less than 5 μm in diameter were not accounted for in all the organs investigated, but a wide diffusion in the whole body at very low density was presumed.     

Dielectrophoretic manipulation of particle mixtures employing asymmetric insulating posts

A novel scheme for particle separation with insulator‐based dielectrophoresis (iDEP) was developed. This technique offers the capability for an inverted order in particle elution, where larger particles leave the system before smaller particles. Asymmetrically shaped insulating posts, coupled with direct current (DC) biased low‐frequency alternating current (AC) electric potentials, were used to successfully separate a mixture of 500 nm and 1 μm polystyrene particles (size difference of 0.5 μm in diameter). In this separation, the 1 μm particles were eluted first, demonstrating the discriminatory potential of this methodology. To extend this technique to biological samples, a mixture containing Saccharomyces cerevisiae cells (6.3 μm) and 2 μm polystyrene particles was also separated, with the cells being eluted first. The asymmetric posts featured a shorter sharp half and a longer blunt half; this produced an asymmetry in the forces exerted on the particles. The negative DC offset produced a net displacement of the smaller particles toward the upstream direction, while the post asymmetry produced a net displacement of the larger particles toward the downstream direction. This new iDEP approach provides a setup where larger particles are quickly concentrated at the outlet of the post array and can be released first when in a mixture with smaller particles. This new scheme offers an extra set of parameters (alternating current amplitude, DC offset, post asymmetry, and shape) that can be manipulated to obtain a desired separation. This asymmetric post iDEP technique has potential for separations where it is important to quickly elute and enrich larger and more fragile cells in biological samples.     

Laser Microprobe Mass Analysis of Individual Antarctic Aerosol Particles

Abstract

Individual Antarctic aerosol particles in the 0.5–4 μm aerodynamic diameter range were analyzed using laser microprobe mass analysis (LAMMA). As they were sampled near the ocean, the great majority consists of seasalt, transformed to various degrees in the atmosphere. Major alterations include the association of an excess sulfate and methane sulfonate with these particles. Sulfate-rich particles containing little or no chloride were found mostly in the smallest size fraction (0.5–1 μm), where they account for some 5% of all particles: they are most likely highly transformed seasalt. Aluminosilicates, on the other hand, only appear among the coarser particles: they represent 2% of the particulates in the 2–4 μm range. The remainder of the aerosol consists of organic, Fe-rich, K-rich and Zn-rich particles. The latter groups have very low abundances: always less than 1% of the population of the impactor stage(s) onto which they were collected.     

Determination of trace-metal concentrations in size-classified atmospheric particles by ETV-ICP-MS

Atmospheric particles were sampled and fractionated according to their size by a cascade impactor in Berlin, capital city of Germany, on the Brocken, peak of the Harz mountains and on the Szrenica peak in the Giant mountains, Republic Poland. The fractionated particles were collected on small graphite targets and subsequently analyzed by ETV-ICP-MS. Distribution curves were measured showing trace-metal contents in air versus the aerodynamic particle diameter for the elements Pb, Ag, Cd and Tl. Despite good element correlation, the distribution curves differ significantly for the three sampling locations. The limits of detection for the elements of concern were in the pg/m³ range at a sampling time of 4 h. An attempt was made to determine single particles: in urban aerosols a content was found of 1 · 10^–13 g Tl and 9 · 10^–13 g Ag in single particles of the size fraction < 7.5 μm and > 3.45 μm.     

Proton microprobe analysis of interplanetary dust particles

Interplanetary dust particles (IDPs) are typically <10 μm in diameter and <10^?9 g in mass on collection. The Heidelberg proton microprobe (beam spot ?2 × 3 μm²) allows non-destructive detectio of trace elements in such samples. Two IDPs (Zodiac and Bounce) were examined. To evaluate the proton-induced x-ray spectra quantitatively, the x-ray production rates for thin samples were calculated with a computer routine; the elemental ratios of the samples normalized to silicon or iron were evaluated. The ratios found for the Zodiac sample agree within a factor of two with those of cosmic abundance. The other IDP showed depletion in Ca, K, Zn and S.     

Single particle analysis using fluidic, optical and electrophoretic force balance in a microfluidic system

A unique microfluidic system is developed which enables the interrogation of a single particle by using multiple force balances from a combination of optical force, hydrodynamic drag force, and electrophoretic force. Two types of polystyrene (PS) particles with almost identical size and refractive index (plain polystyrene (PS) particle - mean diameter: 2.06 μm, refractive index: 1.59; carboxylated polystyrene (PS-COOH) particles - mean diameter: 2.07 μm, refractive index: 1.60), which could not be distinguished by optical chromatography, reveal different electrokinetic behaviors resulting from the difference in their surface charge densities. The PS-COOH particles, despite their higher surface charge density when compared to the PS particles, experience a lower electrophoretic force, regardless of ionic strength. This phenomenon can be understood when the more prominent polarization of the counter ion cloud surrounding the PS-COOH particles is considered. The surface roughness of the carboxylated particles also plays an important role in the observed electrokinetic behavior.     

Kinetic optimisation of open-tubular liquid-chromatography capillaries coated with thick porous layers for increased loadability

The kinetic optimisation of open-tubular liquid chromatography (OTLC) columns has been revisited by taking the thick-film effects for porous coatings on retention, column resistance, band broadening and mass loadability into account. Considering the most advantageous case (i.e. where the retentive layer allows for the same high internal diffusion coefficient as conventional porous particles), calculations show the need for the development of coating procedures leading to porous films filling up approximately 50-70% of the total column diameter. Furthermore, to achieve optimum kinetic performance for separations of small molecules with total analysis times of less than 8h (k'=9), total column diameters should be less than 6 μm with lengths typically greater than 0.8m for N values of 125,000-500,000 at a pressure of 400 bar. The use of elevated temperature LC (90°C) is also shown to increase the allowable total column diameter to up to 9 μm for a larger range of N values (100,000-880,000).     

Spherical Versus Irregular-Shaped Silica Gel Particles in HPLC

Abstract

With optimised packing procedures, spherical shaped silica gel particles produce 1.5 to 2 times more plates in HPLC than irregular shaped silica gel particles. The lowest reduced plate height obtained by us so far is for 5 μm ROSiL-C₁₈-HL-D and is h: 1.62 for k': 4.5. It is suggested to transform h into 100/h% and to name this the “Chromatographic efficiency”, or a % of the ideal 100% limit. This limit would be an h value equal to the mean particle diameter. Spherical and irregular silica gel particles of 5 and 10 μm particle diameter and with similar physical characteristics have the same permeability in HPLC columns.

Whether a correct column packing procedure is used can be shown by the constancy of plate number and column permeability in function of different packing pressures.     

Particle behavior in thermal plasmas

In this overview, effects exerted on the motion and on heat and mass transfer of particulates injected into a thermal plasma are discussed, including an assessment of their relative importance in the context of thermal plasma processing of materials. Results of computer experiments are shown for particle sizes ranging from 5–50 μm, and for alumina and tungsten as sample materials. The results indicate that (i) the correction terms required for the viscous drag and the convective heat transfer due to strongly varying properties are the most important factors; (ii) noncontinuum effects are important for particle sizes <10 μm at atmospheric pressure, and these effects will be enhanced for smaller particles and/or reduced pressures; (iii) the Basset history term is negligible, unless relatively large and light particles are considered over long processing distances; (iv) thermophoresis is not crucial for the injection of particles into thermal plasmas; (v) turbulent dispersion becomes important for particle <10 μm in diameter; and (vi) vaporization describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas.     

Production of porous silica microparticles by membrane emulsification

A method for the production of near-monodispersed spherical silica particles with controllable porosity based on the formation of uniform emulsion droplets using membrane emulsification is described. A hydrophobic metal membrane with a 15 μm pore size and 200 μm pore spacing was used to produce near-monodispersed droplets, with a mean size that could be controlled between 65 and 240 μm containing acidified sodium silicate solution (with 4 and 6 wt % SiO(2)) in kerosene. After drying and shrinking, the final silica particles had a mean size in the range between 30 and 70 μm. The coefficient of variation for both the droplets and the particles did not exceed 35%. The most uniform particles had a mean diameter of 40 μm and coefficient of variation of 17%. By altering the pH of the sodium silicate solution and aging the gel particles in water or acetone, the internal structure of the silica particles was successfully modified, and both micro- and mesoporous near-monodispersed spherical particles were produced with an average internal pore size between 1 and 6 nm and an average surface area between 360 and 750 m(2) g(-1). A material balance and particle size analysis provided identical values for the internal voidage of the particles, when compared to the voidage as determined by BET analysis.     

Effects of pretreatment temperature on the analysis of size-fractionated aerosol particles using ToF-SIMS

Size-fractionated aerosol particles were collected with a MOUDI 10-stage cascade impactor from an urban roadside place in a downtown area of Hong Kong. Fine aerosol particulate samples from stage 6 (aerodynamic particle diameter between 0.56 and 1 μm) and stage 9 (aerodynamic particle diameter between 0.10 and 0.18 μm) were pretreated at a chosen temperature, including −100°C, −50°C, 25°C, and 60°C, in a load lock chamber and then analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS) at the same temperature (−100°C). Principal component analysis (PCA) was applied to further analyze ToF-SIMS spectra of aerosol particles with different pretreatment temperatures from two selected stages. ToF-SIMS results showed that the intensities of aliphatic hydrocarbon ions such as C₄H₇⁺ and C₄H₉⁺ and amine ions such as C₂H₈N⁺ and C₄H₁₂N⁺ decreased with an increase of the pretreatment temperature under ultrahigh vacuum conditions. We have shown that analyses of this type of aerosol particles using ToF-SIMS should not be conducted at ambient temperature but at low temperature (eg, −50°C). In addition, we also developed a procedure that can be used to analyze aerosol particle samples under ultrahigh vacuum environment.     

Micro-impedance cytometry for detection and analysis of micron-sized particles and bacteria

The sensitivity of a microfluidic impedance flow cytometer is governed by the dimensions of the sample analysis volume. A small volume gives a high sensitivity, but this can lead to practical problems including fabrication and clogging of the device. We describe a microfluidic impedance cytometer which uses an insulating fluid to hydrodynamically focus a sample stream of particles suspended in electrolyte, through a large sensing volume. The detection region consists of two pairs of electrodes fabricated within a channel 200 μm wide and 30 μm high. The focussing technique increases the sensitivity of the system without reducing the dimensions of the microfluidic channel. We demonstrate detection and discrimination of 1 μm and 2 μm diameter polystyrene beads and also Escherichia coli. Impedance data from single particles are correlated with fluorescence emission measured simultaneously. Data are also compared with conventional flow cytometry and dynamic light scattering: the coefficient of variation (CV) of size is found to be comparable between the systems.     

聚苯胺/钛酸钡纳米复合粒子的制备与表征

采用原位复合法制备出聚苯胺/钛酸钡复合粒子,借助TEM、XRD、FT-IR、 XPS、TG等分析手段研究了复合粒子的形貌、结构及其热性能.结果表明,复合粒子的粒径为1 μm左右,BaTiO3以40 nm左右的晶粒分散于聚苯胺基体之中,聚苯胺与钛酸钡之间存在化学键合作用,同时在一定程度上减少了纳米粒子的团聚.     

Seeded polymerization of vinyl acetate using monodisperse poly(vinyl acetate) latex particles

The seeded polymerizations of vinyl acetate, using monodisperse poly(vinyl acetate) latex particles prepared in the absence of emulsifiers with potassium persulfate, have been investigated at 70°C with potassium persulfate as an initiator. New small particles were formed in the system containing a small amount of seed particles, but were not observed in the system containing a large amount of seed particles. The size of the secondary particles increased, and their number decreased, with an increase in the seed particle number. The minimum diameter of PVAc particles, which are stabilized by the sulfate ion groups bound at the end of polymer chains during polymerization, was determined to be 0.12 μm diameter from the limiting total surface area of seed particles which prevented further secondary nucleation. The minimum diameter of the particles increased as the speed of the stirrer increased. The new small particle number calculated using this value agreed well with that formed in the seeded polymerization.     

Synthesis of cross-linked polymer microspheres in supercritical carbon dioxide

Herein we report the synthesis of highly cross-linked polymers based on divinylbenzene by heterogeneous polymerization in supercritical CO₂ (scCO₂). The polymers were isolated in the form of discrete microspheres (diameter = 1.5–5 μm) in good yields (≥90%), in the absence of any stabilizers. In the presence of a CO₂-soluble polymeric stabilizer, much smaller particles (diameter <0.5 μm) were formed in high yields (≥95%) by emulsion polymerization in scCO₂.     

Preparation and Use of Polyurethane Enzyke Particles

The preparation and use of immobilized enzyme particles by disrersior and radiation polymerization technique in polyurethane prepolymer using polylene-2,4-diisocyanate, 2-hydroryethyl methacrylate, pentamethylene glycol, and cellulase are presented. The enzyme was added to form the particles (10–100C μm in diameter) under stirring of the mixture containing the prepolymer and enzyme solution, in which the enzyme was covalently bound to the surface of the particle. The size of the particles varied with the concentration of the enzyme and monomer. The enzymatic activity of the particles varied with the particle diameter, composition of monomer, and dispersion temperature.