Assemblies of poly(styrene/⇌-tert-butoxy-ω-vinyl-benzyl-poryglycidol) Microspheres with different diameters deposited on mica plates

Formation of poly(styrene/α-tert-butoxy-ω-vinyl-benzyl-polyglycidol) microsphere assemblies on mica plates modified with 3-aminopropyltriethoxysilane was investigated. Microsphere assemblies contained two types of particles similar with respect of their chemical structure but with different diameters (D _n = 1000 and 350 nm). Methods of particle deposition included: deposition from water suspension of a mixture of small and large particles on mica plates placed at the bottom of suspension container, deposition of particles from a drop of ethanol suspension (containing large and small microspheres) placed on the mica substrate, deposition of microspheres on modified mica plates crossing the liquid-air interface-sequential deposition of large and small particles, and one-batch deposition from a mixed water suspension of large and small microspheres. Deposition from water suspension containing large and small microspheres on plates placed on the bottom of suspension container yielded assemblies with large particles randomly distributed among the small ones. Fraction of large particles in adsorbed particle assembly was smaller than fraction of large particles in suspension. Particle assemblies prepared by placement of ethanol suspension of large and small microspheres on mica were composed of quite regularly distributed large particles among the small ones. A two step process consisting of withdrawal of mica plate from water suspension of large particles and then on using this plate as substrate in a second step during which the plate was withdrawn from suspension of small particles yielded particle assemblies containing aggregates of large particles randomly distributed among the small ones. Withdrawal of mica plates from water suspension of large and small microspheres resulted in particle assemblies composed of regularly distributed stripes of large and small microspheres. Formation of the described above microsphere assemblies is possible only in case of reversible adsorption of particles.     

Effects of particle size segregation on crossflow microfiltration performance: Control mechanism for concentration polarisation and particle fractionation

Although the principal mechanisms of crossflow microfiltration (MF) are well-known, the practical applicability of the resulting microfiltration models is still limited. This can be largely attributed to the lack of understanding of effects of polydispersity in the particulate suspensions, as relevant to concentration polarisation in MF. This paper describes an investigation of concentration polarisation behaviour of bidisperse suspensions, in the regime where shear-induced diffusion is the dominant back-transport mechanism. In the transient flux regime, the particle deposition onto the membrane was monitored by means of confocal scanning laser microscopy. As in accordance with the linear dependence of the shear-induced diffusivity on a², only the small particles in the bidisperse suspensions were found to deposit onto the membrane. The back-transport flux that was calculated from the deposition rate and the actual permeate flux, was found to be independent of the composition of the suspension, whereas it was equal to the back-transport flux of a monodisperse suspension of the small particles only, with a similar total particle fraction. These results can be explained with the occurrence of particle size segregation in the feed flow, which leads to an enrichment with small particles of the suspension near the membrane. The findings are also shown to be relevant to particle fractionation processes by MF. In such fractionation processes, particle size segregation is found to have a strong effect on the separation characteristics such as particle size and fat content of the permeate. A polydisperse suspension could be fractionated using a membrane having a pore size larger than the largest particles present. The fractionation thus results not from size exclusion in the membrane, but from segregation effects in the feed channel.     

Micronization of Iron Oxide Particles Using Gas Antisolvent Process

Iron oxide particles were micronized by supercritical carbon dioxide (CO₂) as an antisolvent in a batch gas antisolvent (GAS) process. In the present study, the feasibility of GAS process to micronize the iron oxide particles using dimethyl sulfoxide (DMSO) as a solvent was investigated. In this direction, particle size and morphology changes were investigated with changing solution pressure (80–150 bar), temperature (308.15–328.15 K), and concentration (1.5–6 g/l). Based on the different experimental conditions, the particle size of the original iron oxide was decreased in the range of 17.25 to 4.23 µm, which shows a the success of the GAS process to reduce the particle size of the intact iron oxide particles. Simultaneously, morphology changes were observed starting from the irregular morphology for synthesized particles to more regular shapes that included fused and spherical-fused particles.     

Analytical scale purification of zirconia colloidal suspension using field programmed sedimentation field flow fractionation

Sedimentation field flow fractionation was used to obtain purified fractions from a polydispersed zirconia colloidal suspension in the potential purpose of optical material hybrid coating. The zirconia particle size ranged from 50/70 nm to 1000 nm. It exhibited a log-Gaussian particle size distribution (in mass or volume) and a 115% polydispersity index (P.I.). Time dependent eluted fractions of the original zirconia colloidal suspension were collected. The particle size distribution of each fraction was determined with scanning electron microscopy and Coulter sub-micron particle sizer (CSPS). These orthogonal techniques generated similar data. From fraction average elution times and granulometry measurements, it was shown that zirconia colloids are eluted according to the Brownian elution mode. The four collected fractions have a Gaussian like distribution and respective average size and polydispersity index of 153 nm (P.I. = 34.7%); 188 nm (P.I. = 27.9%); 228 nm (P.I. = 22.6%), and 276 nm (P.I. = 22.3%). These data demonstrate the strong size selectivity of SdFFF operated with programmed field of exponential profile for sorting particles in the sub-micron range. Using this technique, the analytical production of zirconia of given average size and reduced polydispersity is possible.     

悬浮液进样电感藕合等离子体发射光谱中颗粒的输运和蒸发行为

以碳化硼为例,研究了悬浮液雾化进样中的粒子在传输和蒸发过程中的行为,并对分析结果出现负偏离的原因进行了详细探讨.对比悬浮液颗粒的原始粒径分布和经过传输过程后的粒径分布,获得到达等离子体的颗粒粒径上限小于10 Am.样品中存在的部分超大粒径的颗粒(d>>10 μm)会严重影响可传输区域颗粒(d<10 μm)的质量运输效率...     

CFD simulation of floating particles suspension in a stirred tank

Computational fluid dynamics (CFD) simulations were performed to predict the floating particles suspension in a baffled tank stirred by a standard Rushton turbine. An Eulerian multiphase model and a standard k-ε turbulence model with mixture properties were used in the CFD simulation. The impeller rotation was solved using a moving reference frame method. Flow pattern, power number and solid holdup distribution were obtained and compared with the results in literature. The effects of operating condition on floating particles suspension characteristics were studied. It indicated that the influences of impeller speed and solid loading on particle suspension varied with particle sizes. For small particles, the impeller speed and solid loading have no obvious effects on solid holdup distribution and suspension quality. For large particles, particle suspension quality becomes better first, and then keeps almost unchanged with enhancing of the impeller speed. Suspension quality is better for higher solid loading of large particles. Within the scope of the present study, solid loading has no great effect on suspension quality. Suspension quality becomes worse with increasing of the particle size. Large particles are easy to accumulate in the centres of the liquid free surface and the upper circular loop, and the vicinity of the shaft.     

Size segregation in a fluid-like or gel-like suspension settling under gravity or in a centrifuge

We investigate size segregation effects in a bidisperse concentrated suspension when slowly settling under gravity or when submitted to a centrifugal field. Experiments are carried out with PMMA spheres of two different mean diameters (190 and 25 microm) suspended in a hydrophobic index-matched fluid. Spatial repartitions of both small and large spheres and velocity fluctuations of particles are measured using fluorescently labeled PMMA spheres and a particle-image-velocimetry method. Large particles behave as hard spheres in purely hydrodynamic interactions, while small spheres interact through weakly attractive forces. For a small amount of small spheres among large ones, the suspension remains fluid during settling and the organization of the velocity field of particles into finite-sized structures also called "blobs" promotes size segregation. A larger proportion of weakly attractive small spheres in the bidisperse suspension causes a considerable slowdown of the settling process under gravity and the occurrence of a large-scale collective behavior together with a loss of size segregation. When centrifuging the gel-like bidisperse suspension, a shear-induced melting of the particle network induces a spectacular segregation of species. As a consequence, aging tests of soft yielding materials using centrifugation methods are not representative of the shelf-life stability of the products. A tentative model based on the competition between viscous stresses acting upon particles and adhesive stresses gives a correct estimate of the critical stationary acceleration for the destabilization of the particle network and the onset of size segregation in a gel-like suspension.     

Chromatography of Suspensions,An Absolute Particle Size Detector Based on Turbidity-spectra Analysis - a Simulation Study

Abstract

In the chromatography of particle suspensions the use of a variable wavelength spectrophotometer can provide turbidity spectra continuously with retention volume. As suggested by Hamielec [1] this device could form the basis for an absolute particle size detector provided the size distribution in the detector cell could be represented by a known distribution function. In this work it is shown that the two parameter log-normal distribution function is an adequate representation of the detector cell contents. Further a computational scheme is outlined whereby the distribution parameters and the number of particles in the detector cell are calculated as a function of retention volume. It is then possible to obtain size distribution information of the original suspension.     

Dispersion copolymerization of styrene and divinylbenzene: Synthesis of monodisperse,uniformly crosslinked particles

Monodisperse, crosslinked polystyrene latexes were prepared by the dispersion technique. Some general observations regarding the effect of initial reagent concentrations on final particle size and size distribution are offered, in addition to a detailed discussion concerning the problems encountered with the use of the crosslinker divinylbenzene (DVB) in latex preparation. Particles synthesized in very polar media were found to reach their growth plateau sooner than those made in less polar surroundings. This trend was proposed to be the result of more effective nucleation in polar environments, which increases available surface area, thereby allowing the rapid replacement of monomer consumed within the particle phase during the polymerization. Attempts to favorably influence the growth rate and size distribution of particles during the reaction were unsuccessful, underlining the importance of the nucleation period in defining particle size characteristics. Up to 1% DVB was successfully incorporated in the synthesis of coagulum-free, monodisperse, 5 μm beads, by controlling the entry of the crosslinker into the particle phase during the major particle growth period. Latex stability is proposed to be largely dependent on the mobility of the adsorbed steric stabilizer. © 1995 John Wiley & Sons, Inc.     

Electric double layer for spherical particles in salt-free concentrated suspensions including ion size effects

The equilibrium electric double layer (EDL) that surrounds colloidal particles is essential for the response of a suspension under a variety of static or alternating external fields. An ideal salt-free suspension is composed of charged colloidal particles and ionic countercharges released by the charging mechanism. Existing macroscopic theoretical models can be improved by incorporating different ionic effects usually neglected in previous mean-field approaches, which are based on the Poisson-Boltzmann equation (PB). The influence of the finite size of the ions seems to be quite promising because it has been shown to predict phenomena like charge reversal, which has been out of the scope of classical PB approximations. In this work we numerically obtain the surface electric potential and the counterion concentration profiles around a charged particle in a concentrated salt-free suspension corrected by the finite size of the counterions. The results show the high importance of such corrections for moderate to high particle charges at every particle volume fraction, especially when a region of closest approach of the counterions to the particle surface is considered. We conclude that finite ion size considerations are obeyed for the development of new theoretical models to study non-equilibrium properties in concentrated colloidal suspensions, particularly salt-free ones with small and highly charged particles.     

Influence of the seed polymer on the chromatographic properties of size monodisperse polymeric separation media prepared by a multi-step swelling and polymerization method

Monodisperse polymer particle-based separation media were prepared by a multi-step swelling and polymerization method with two pairs of monomers and two porogenic solvents. Their chromatographic properties were compared to those of beads prepared by a corresponding suspension polymerization method without the use of seed polymer to ascertain the influence of the seed polymer on their porous structures. A large change in porous structure was observed when the swollen particle consisting of monomers and porogenic solvents contained at least one good solvent for the polystyrene seed polymer, allowing it to remain in the polymerizing medium. In contrast, when the polystyrene seed particle was excluded from the swollen oil droplets, due to its poor solubility in the monomers and the porogenic solvents, there was no difference in the chromatographic properties such as pore volume, pore size, pore size distribution, or retention selectivity between the multi-step swelling and polymerization method and the suspension polymerization method. Since the only difference between the multi-step swelling and polymerization method and the suspension method is the use of the seed polymer, it appears that a very small amount (< 1% v/v) of seed polymers in the enlarged swollen droplets plays an important role as a porogen and affects the porous structure as well as the chromatographic properties of the monodisperse polymer particle-based separation media. © 1993 John Wiley & Sons, Inc.     

Particle formation under monomer‐starved conditions in the semibatch emulsion polymerization of styrene. I. Experimental

Particle formation and particle growth compete in the course of an emulsion polymerization reaction. Any variation in the rate of particle growth, therefore, will result in an opposite effect on the rate of particle formation. The particle formation in a semibatch emulsion polymerization of styrene under monomer‐starved conditions was studied. The semibatch emulsion polymerization reactions were started by the monomer being fed at a low rate to a reaction vessel containing deionized water, an emulsifier, and an initiator. The number of polymer particles increased with a decreasing monomer feed rate. A much larger number of particles (within 1–2 orders of magnitude) than that generally expected from a conventional batch emulsion polymerization was obtained. The results showed a higher dependence of the number of polymer particles on the emulsifier and initiator concentrations compared with that for a batch emulsion polymerization. The size distribution of the particles was characterized by a positive skewness due to the declining rate of the growth of particles during the nucleation stage. A routine for monomer partitioning among the polymer phase, the aqueous phase, and micelles was developed. The results showed that particle formation most likely occurred under monomer‐starved conditions. A small average radical number was obtained because of the formation of a large number of polymer particles, so the kinetics of the system could be explained by a zero–one system. The particle size distribution of the latexes broadened with time as a result of stochastic broadening associated with zero–one systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3940–3952, 2001     

Structure-activity relationship in HC-SCR of NOx by TEM, O2-chemisorption, and EDXS study of Ag/Al2O3

Ag/alumina catalysts with different silver loading (1.28-6 wt %) for lean NO reduction activity were prepared by impregnation and the incipient wetness method. Complementary HRTEM, HAADF, O2-chemisorption, and EDXS studies were applied to investigate the dependence between silver particle size and catalytic activities of the prepared materials. The catalyst with the lowest silver loading (1.28 wt %) was found to be the most active catalyst in terms of reacted NO molecules per mole of silver. On the basis of the HRTEM, HAADF, and O2-chemisorption studies it could be concluded that the mean particle size or particle size distribution of the samples alone could not explain the big difference in the activities. EDXS analyses showed on the other hand that all of the samples were very heterogeneous in terms of particle size distribution, e.g., including both small and very big particles. Furthermore, both metallic silver and mainly hexagonal silver oxide (Ag2O) were found to be present in the samples. Despite the valuable information provided by ex situ characterization of the prepared samples, it needs to be emphasized that establishing a structure-reactivity relationship for this type of catalyst requires in situ characterization.     

Preparation and Characterization of Cubosomal KIOM-C Suspension and Investigation on In Vitro Small Intestinal Absorption of Baicalin

KIOM-C suspension and cubosome/KIOM-C suspension were prepared in various buffer solution of different pHs by a sonication method. KIOM-C particles were unstable in terms of time-dependent change in the size and the zeta potential. The fluctuation in the size and the zeta potential of KIOM-C particles was effectively damped by cubosome. The shape of KIOM-C particles was irregular and the size was hundreds to thousands of nm. Cubosome/KIOM-C particles exhibited stripes on their surfaces and the size was hundreds of nm. Regardless of the pH values (pH 2.0–10.0) of media, baicalin, a major component of KIOM-C, was chemically stable for 48 hours at a room temperature. Cubosome markedly enhanced the stability of baicalin particles against sedimentation. EDTA significantly enhanced the in vitro small intestinal absorption of baicalin, but MO cubosome hardly promoted.     

Colloidal stability of PVC primary particles in vinyl chloride

The electrostatic contribution to the colloidal stability of PVC primary particles (R=0.15 m) dispersed in vinyl chloride, was calculated using models based on the Coulombic interactions and the DLVO theory. The calculations were based on: a) the particle charge as obtained from literature data on the electrophoretic mobility of PVC primary particles in VCM and b) on estimates of the Debye length as obtained from measurements of the electrical conductivity of VCM and of solutions of Bu₄NBF₄ in VCM.The calculations showed that particle stability would decrease with particle size (experimentally-observed behaviour), only if the particle charge increased with size at a lower rate than in proportion to particle radius.The calculations also suggest that particle growth may be governed by a competitive growth mechanism of electrostatic origin. Particle growth is assumed to occur by absorption of many small, weakly charged basic particles from the monomer phase. According to the calculations, the electrostatic interaction between primary and basic particles may be such that the growth of the smaller primary particles is favoured over that of the larger ones.     

Effects of Microcrystalline Cellulose on Suspension Stability of Cocoa Beverage

The rheological properties and particle size distributions of cocoa beverage as well as aggregate structures of solid particles were studied to elucidate the effects of microcrystalline cellulose (MCC) on suspension stability of solid particles in cocoa beverage. Fluidity curve, dynamic viscoelasticity, particle size distribution, and SEM observation were made for beverage samples containing 0.1–0.5 wt% MCC and 11 model samples with various combinations of six ingredients. This revealed that cocoa and MCC particles are highly cohered into an aggregate and the aggregated particles further interact weakly with the milk component, leading to stabilization of the whole system of cocoa beverage.     

Aggregation phenomena in the suspension polymerization of VCM

In the suspension polymerization of VCM, insoluble polymer particles are formed inside the monomer droplets. The growth and aggregation of these particles are responsible for important polymer properties, such as porosity. It is well established that the most characteristic polymer particles, the primary particles, are of a narrow distribution with a size (diameter) ranging from 0.10–0.20 m. This work studied the formation of primary particles based on the aggregation phenomena that take place inside a monomer droplet. This was done by formulating a population balance equation, which was based on the following considerations: a) polymerization occurs in both the monomer and the polymer phases; b) there is continuous formation of the basic particles in the monomer phase; c) the growth of the polymer particles occurs as a result of both polymerization in the polymer phase and aggregation of the particles; d) the colloidal properties of the particles that are responsible for the aggregation phenomena were considered to be the net result of attraction and repulsion energies.It was shown that for particles carrying a constant charge it was not possible to predict the formation of primary particles of size 0.10–0.20 m. The particle size distribution had a mode diameter equal to the diameter of the basic particles. Consequently, the particle charge was allowed to vary in a way proportional to the particle radius raised to a power coefficient. For values of the coefficient greater than zero, i. e., when the particle charge increased during polymerization, the aggregation of the basic particles was efficient enough to result in the formation of large primary particles.     

Study of poly(St/BA/MAA) copolymer latexes with trimodal particle size distribution

A new strategy was developed for producing a polymer latex with trimodal particle size distribution by adding a second seed of polymer particles and some additional surfactants during polymerization. The polymerization was investigated by following the variation of the particle size, the size distribution, the number of particles, the surface tension and surfactant surface coverage at different stages of the polymerization process. The results showed that both the size and the size distribution can be easily controlled by varying the amount of additional surfactants and the second seed of polymer particles. The secondary nucleation was achieved when the surface coverage of particles was over 70%, and the amount of small particles formed increased with increasing amount of additional surfactants. The introduction of the additional surfactants had no significant effect on the size and number of middle particles, but reduced the size of large particles and caused the number of large particles to remain more stable because of the suppression of limited flocculation. Copyright © 1998 John Wiley & Sons, Ltd.     

Synthesis of liquid‐filled nanocapsules via the miniemulsion technique

This study describes the synthesis of well‐defined nanocapsules via the miniemulsion technique. Pentaerythritol tetrakis(3‐mercaptopropionate) (TetraThiol) or 1,6‐hexanediol di(endo, exo‐norborn‐2‐ene‐5‐carboxylate) (DiNorbornene) is used as the oil phase. TetraThiol is encapsulated via the miniemulsion technique without polymerization, as this monomer would simultaneously act as a chain‐transfer agent, and DiNorbornene is encapsulated via miniemulsion polymerization of styrene. Various styrene‐maleic anhydride (PSMA) copolymers and poly(styrene‐maleic anhydride)‐block‐polystyrene (PSMA‐b‐PS) block copolymers were used as surfactant for the synthesis of well‐defined nanocapsules with TetraThiol as the core material. The nanocapsules had a diameter of 150–350 nm and the particle size distribution was narrow. The use of PSMA‐b‐PS block copolymers as surfactant in combination with post‐addition of formaldehyde provided improved stability to the nanocapsules. DiNorbornene was encapsulated via miniemulsion polymerization of styrene, and a stable latex with a bimodal particle size distribution was obtained. The distribution of small particles had a size of 60 nm and the distribution of large particles had a size of 150 nm. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

TiO2 *nH2 O凝胶预处理对水热合成SrTiO3 粉的影响

以TiCl4为钛源, 首先制备TiO2 * nH2O凝胶, 然后在80℃的水热条件下制备了SrTiO3粉.利用X射线衍射(XRD)、透射电子显微镜(TEM)和红外光谱(FTIR)研究了TiO2 * nH2O凝胶水洗方式、阴离子(Cl-和NO3-)以及TiO2 * nH2O热处理对SrTiO3粉性能的影响.结果表明, 水洗和热处理都能使TiO2 * nH2O凝胶产生晶化; TiO2 * nH2O的晶化程度对产物SrTiO3颗粒的粒度和粒度分布有很大影响,以非晶质TiO2 * nH2O为钛源制备的SrTiO3颗粒粒度大且粒度分布宽.以结晶TiO2 * nH2O为钛源制备的SrTiO3颗粒粒度小且粒度分布窄,而且可以得到纳米颗粒.水热反应液相中存在Cl-或NO3-能使产物SrTiO3颗粒粒度稍有增大.综合以上结果, TiO2 * nH2O凝胶水洗对产物颗粒的影响主要是由于使凝胶产生了晶化,而由阴离子脱除产生的影响很小.因此,在不考虑阴离子对其它工程化影响(如设备腐蚀等)的前提下,可采用热处理代替水洗.