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Particle Morphology (particle + morphology)
Selected AbstractsEffect of Calcination Conditions and Excess Alkali Carbonate on the Phase Formation and Particle Morphology of Na0.5K0.5NbO3 PowdersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2007Pornsuda Bomlai Sodium-potassium niobate [Na0.5K0.5NbO3] powders were prepared following the conventional mixed oxide method. An orthorhombic XRD pattern, consistent with single-phase Na0.5K0.5NbO3, was obtained after calcination at 900°C for 6 h. Introducing 5 mol% excess Na2CO3 and K2CO3 into the starting mixture allowed milder calcination conditions to be used, for example 800°C for 2 h. Primary particles in 5 mol% excess samples were cuboid, with maximum sizes of ,2.5 ,m. Equiaxed 0.3,0.4-,m particles were formed for non-excess powders, and also for powders prepared with 1 and 3 mol% excess alkali carbonates. The results suggest liquid formation during calcination of the excess 5-mol% starting powders. [source] Influence of Particle Morphology and Flow Conditions on the Dispersion Behavior of Fumed Silica in Silicone PolymersPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2004John Boyle Abstract The dispersion behavior of agglomerates of several grades of fumed silica in poly(dimethyl siloxane) liquids has been studied as a function of particle morphology and applied flow conditions. The effects of primary particle size and aggregate density and structure on cohesivity were probed through tensile and shear strength tests on particle compacts. These cohesivity tests indicated that the shear strength of particle compacts was two orders of magnitude higher than the tensile strength at the same overall packing density. Experiments carried out in both steady and time-varying simple-shear flows indicate that dispersion occurs through tensile failure. In the steady-shear experiments,enhanced dispersion was obtained at higher levels of applied stress and, at comparable levels of applied stress, dispersion was found to proceed faster at higher shear rates. Experiments conducted in time-varying flows further corroborated the results obtained in tensile cohesivity tests. Experiments in which the mean and maximum stresses in the time-varying flows were matched to the stresses produced in steady shear flows highlight the influence of flow dynamics on dispersion behavior. [source] Controlling the Size and Morphology of TiO2 Powder by Molten and Solid Salt SynthesisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Banasri Roy Nano and submicrometer scale titanium oxide (TiO2) powders were synthesized by solid and molten salt synthesis (SSS and MSS) from amorphous titanium hydroxide precipitate. Sodium chloride (NaCl) and dibasic sodium phosphate (Na2HPO4·2H2O, DSP) separately or as mixture with different weight ratios were used as the salts. At the eutectic salt composition (20% DSP/80% NaCl), the microstructure and phase composition of the TiO2 was changed from equiaxed nanoparticles of anatase with size ,40,50 nm, to mixed microstructure of bundle and acicular particles of rutile with 0.05,0.2 ,m diameter, 6,10 ,m length, and aspect ratio 20,60 depending on treatment time and temperature. At high temperature (825°C) and long time (30 h), microstructural differences were significant for the powders treated with different salts. Particle morphologies ranged from equiaxed, to acicular, to bundles, to nanofibers with very high aspect ratio. At lower treatment temperature (725°C) for shorter time (3 h), the morphology of the products did not change with different salt compositions, but the crystallite sizes changed appreciably. Different starting titanium precursors influenced particle size at lower temperature and time. Titanium hydroxide heat treated without salt resulted in significant grain growth and fused secondary particles, as compared with more finely separated and lightly agglomerated powders resulting from SSS and MSS treatments. [source] Polymerization of methyl methacrylate in the presence of a nonpolar hydrocarbon solvent.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Abstract This article presents the ternary phase diagram for methyl methacrylate (MMA), poly(methyl methacrylate) (PMMA), and n -hexane system at 70°C. It was constructed by both theoretical calculations and online laser light scattering (LLS) technique. In situ polymerization of MMA in a nonpolar nonsolvent carried out in a LLS cell provides a new means for the accurate detection of the cloud points of highly viscous polymer mixtures, with polymer weight fractions over 0.6. The ternary phase diagram measured in this study can be used to design the reaction conditions for the precipitation and/or dispersion polymerization in a nonpolar nonsolvent medium where polymerization kinetics as well as polymer particle morphologies are strongly affected by thermodynamic phase separation phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Electrosprayed polymer particles: Effect of the solvent propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Chul Ho Park Abstract Electrospraying technology has been studied in many fields to produce particles of various substances from nanoscale to microscale sizes. Unlike pure liquids, droplets formed by electrospraying that are comprised of polymer solutions undergo additional solidification processes involving solvent evaporation, which primarily determine the particle size and morphology. Herein, the effects of the solvent properties on the morphology and dimensions of solidified particles were systematically studied. In general, the size of the solidified spherical particles with smooth surfaces reflected that of the initially formed liquid droplets, which could partially be estimated by theoretical equations developed for pure liquids. Particle sizes increased with an increase in polymer content and a decrease in the boiling point of the volatile solvent. Inhomogeneous drying processes related to phase separation or skin formation resulted in hollow, cuplike, and porous particle structures, with particle sizes and morphologies that were outside of the scope of the theoretical treatments. The selection of a proper solvent or solvent mixture seemed to be a convenient way to control the particle morphologies, such as hollow, cuplike, or porous structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] An examination of binding motifs associated with inter-particle interactions between facetted nano-crystals of acetylsalicylic acid and ascorbic acid through the application of molecular grid-based search methods,JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2009R.B. Hammond Abstract Grid-based intermolecular search methods using atom,atom force fields are used to assess the structural nature of potential crystal,crystal interfacial binding associated with the examination of representative pharmaceutical formulation components, viz acetylsalicylic acid (aspirin) and ascorbic acid (vitamin C). Molecular models of nano-sized molecular clusters for these two compounds, shaped in accordance with an attachment energy model of the respective particle morphologies, are constructed and used together with a grid-based search method to model the likely inter-particle interactions. The most-stable, mutual alignments of the respective nano-clusters based on their interaction energies are identified in the expectation that these are indicative of the most likely inter-particle binding configurations. The stable inter-particle binding configurations identified reveal that the number of interfacial hydrogen bonds formed between the binding particles is, potentially, an important factor in terms of the stability of inter-particle cohesion. All preferred inter-particle alignments are found to involve either the (1,0,0) or the (1,1,0) face of aspirin crystals interacting with a number of the growth forms of ascorbic acid. Four main types of interfacial hydrogen bonds are found to be associated with inter-particle binding and involve acceptor,donor interactions between hydroxyl, carbonyl, ester and lactone acceptor groups and hydroxyl donor groups. This hydrogen bonding network is found to be consistent with the surface chemistry of the interacting habit faces with, in general, the number of hydrogen bonds increasing for the more stable alignments. The likely usefulness of this approach for predicting solid-state formulation properties is reviewed. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4589,4602, 2009 [source] Highly magnetic latexes from submicrometer oil in water ferrofluid emulsionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2006Franck Montagne Abstract The synthesis of functionalized submicrometer magnetic latex particles is described as obtained from a preformed magnetic emulsion composed of organic ferrofluid droplets dispersed in water. Composite (polystyrene/,-Fe2O3) particles were prepared according to a two-step procedure including the swelling of ferrofluid droplets with styrene and a crosslinking agent (divinyl benzene) followed by seeded emulsion polymerization with either an oil-soluble [2,2,-azobis(2-isobutyronitrile)] or water-soluble (potassium persulfate) initiator. Depending on the polymerization conditions, various particle morphologies were obtained, ranging from asymmetric structures, for which the polymer phase was separated from the inorganic magnetic phase, to regular core,shell morphologies showing a homogeneous encapsulation of the magnetic pigment by a crosslinked polymeric shell. The magnetic latexes were extensively characterized to determine their colloidal and magnetic properties. The desired core,shell structure was efficiently achieved with a given styrene/divinyl benzene ratio, potassium persulfate as the initiator, and an amphiphilic functional copolymer as the ferrofluid droplet stabilizer. Under these conditions, ferrofluid droplets were successfully turned into superparamagnetic polystyrene latex particles, about 200 nm in size, containing a large amount of iron oxide (60 wt %) and bearing carboxylic surface charges. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2642,2656, 2006 [source] Acorn-Shape Polymeric Nano-Colloids: Synthesis and Self-Assembled FilmsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 2 2010Anuradha Misra Abstract These studies show for the first time that the synthesis of two distinct phase-separated copolymers within one colloidal particle, i.e., poly(methyl methacrylate) (PMMA)/n -butylacrylate (nBA) and poly(nBA)/pentafluorostyrene (p-PFS) phases, results in unique acorn-shaped morphologies and are capable of coalescence. Spectroscopic and morphological analysis combined with contact angle measurements as well as thermodynamic modeling reveal that in an effort to create stable heterogeneous two-phase particle morphologies it is essential to provide desirable interfacial energetic conditions during polymerization and to utilise monomers that have a similar glass transition temperature (Tg). Such colloidal particles are stable and are able to self-assemble during coalescence, depending upon the surface energy of a substrate. When a particle monolayer coalesces on a high surface tension substrate, the p-PFS phase expresses itself near the film,air interface, whereas for low surface energy substrates, the p-PFS phase dominates the film,substrate interfacial regions. [source] Constituent Particle Break-Up During Hot Rolling of AA 5182,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2010Nicolas Moulin Aluminum sheet is currently used for body panels on a number of mass-produced vehicles, in particular for closure panels. AA5xxx alloys always contain coarse inter-metallic particles (Alx(Fe,Mn)ySi, Mg2Si) after casting. In the present work inter-metallic particle break-up during hot reversible rolling of AA5182 alloy sheets has been analyzed. The sizes and shapes of inter-metallic particles in as-cast and industrially hot rolled AA5182 alloys sheets were characterized by 3D X-ray tomography observations. The relation between particle break-up and particle morphology was then analyzed statistically and by a micromechanical finite element (FE)-based model. The essential outcomes of the statistical approach may be summarized as follows. The inter-metallic particle population may be described by five morphological parameters. Secondly the comparison of the particle morphology in as cast and industrially rolled sheets leads to the definition of five classes. The evolution of each particle class as function of the rolling strain is provided. The statistical analysis shows which particles break-up. The stresses and strains in inter-metallic particles, embedded in an elasto-viscoplastic aluminum matrix submitted to plane strain compression, were analyzed by an FE model. A new failure criterion was proposed. The essential outcomes of the mechanical approach are as follows: a precise description of stress concentration mechanisms in nonconvex particles, a close description of the parameters controlling particle break-up, and finally a simplified classification of the failure behavior. [source] Molecular Mimetic Self-Assembly of Colloidal ParticlesADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Zhengwei Mao Abstract This article presents an overview of the current progress in molecular mimetic self-assembly of colloidal particles. Firstly, the recent study of colloidal particles at interfaces is highlighted, underlining the mesoscopic mimicry of the surface activity of amphiphilic molecules using colloidal particles. Secondly, various strategies developed thus far to impart colloidal particles with anisotropy in terms of chemical composition, surface chemistry and particle morphology, which are regarded as mesoscopic atoms and molecules, are reviewed. Thirdly, an overview of the current theoretical and experimental results of using the rules of molecular synthesis and self-assembly to direct self-assembly of colloidal particles is presented. Finally, the experimental challenges associated with molecular mimetic self-assembly of colloidal particles are outlined, giving a rather conservative conclusion of the status quo of this new research field with a very optimistic outlook. [source] N,N -Dimethylformamide as a Reaction Medium for Metal Nanoparticle SynthesisADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Isabel Pastoriza-Santos Abstract The versatility of wet chemical methods has rendered them extremely popular for the preparation of metal nanoparticles with tailored size and shape. This Feature Article reviews the use of N,N -dimethylformamide (DMF) for the reduction of metal salts, mainly Au and Ag, while also acting as a solvent. Apart from describing the ability of DMF to reduce metal salts, the effect of different parameters, such as the concentration of capping agent and metal precursors, the presence of preformed seeds acting as catalysts or their crystalline structure, on particle morphology are analyzed. Published reports on the use of different capping agents are summarized, with particular emphasis on the role of poly(vinylpyrrolidone) to determine the morphology of the particles. Finally, a brief overview is provided on the modulation of the optical response in DMF-based metal nanoparticle colloids with tunable size and shape. [source] Nonspherical Noble Metal Nanoparticles: Colloid-Chemical Synthesis and Morphology ControlADVANCED MATERIALS, Issue 16 2010Tapan K. Sau Abstract Metal nanoparticles have been the subject of widespread research over the past two decades. In recent years, noble metals have been the focus of numerous studies involving synthesis, characterization, and applications. Synthesis of an impressive range of noble metal nanoparticles with varied morphologies has been reported. Researchers have made a great progress in learning how to engineer materials on a nanometer length scale that has led to the understanding of the fundamental size- and shape-dependent properties of matter and to devising of new applications. In this article, we review the recent progress in the colloid-chemical synthesis of nonspherical nanoparticles of a few important noble metals (mainly Ag, Au, Pd, and Pt), highlighting the factors that influence the particle morphology and discussing the mechanisms behind the nonspherical shape evolution. The article attempts to present a thorough discussion of the basic principles as well as state-of-the-art morphology control in noble metal nanoparticles. [source] Preparation and properties of waterborne interpenetrating polymer networks composed of polyurethaneurea and graft vinyl ester resinJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2009Teng Su Abstract Various waterborne interpenetrating polymer networks (IPNs) composed of polyurethaneurea (PUU) and graft vinyl ester resin were prepared from polyester polyol, dimethylolpropionic acid, isophorone diisocyanate, ethylenediamine and a well-defined graft vinyl ester resin containing butanol side chains (BO-g-VER). These anionic IPN aqueous dispersions were stable at the ambient temperature for >1 yr, and also had the excellent stability at low and high temperatures. The experimental results showed that the introduction of BO-g-VER network has not only greatly affected the particle morphology, stability and rheological behavior of these aqueous dispersions, but also rendered the films with the augmented surface hydrophobicity as well as the excellent water-resistance performance and mechanical properties. A synergistic effect was observed at a certain BO-g-VER composition (20 wt %) to give significant reinforcement to the PUU, resulting from the compatibility and/or the interpenetration between the PUU network and the BO-g-VER network. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Quantitative evaluation of the prosthetic head damage induced by microscopic third-body particles in total hip replacementJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 4 2001Manuela Teresa Raimondi Abstract The increase of the femoral head roughness in artificial hip joints is strongly influenced by the presence of abrasive particulate entrapped between the articulating surfaces. The aim of the present study is to evaluate the dependence of such damage on the geometry of the particles entrapped in the joint, with reference to the UHMWPE/chrome-cobalt coupling. Five chrome-cobalt femoral heads and their coupled UHMWPE acetabular cups, retrieved at revision surgery after a short period of in situ functioning, have been investigated for the occurrence of third-body damage. This was found on all the prosthetic heads, where the peak-to-valley height of the scratches, as derived from profilometry evaluations, ranged from 0.3,1.3 ,m. The observed damage has been divided into four classes, related to the particle motion while being embedded into the polymer. Two kinds of particle morphology have been studied, spherical and prismatic, with size ranging from 5,50 ,m. In order to provide an estimation of the damage induced by such particles, a finite element model of the third-body interaction was set up. The peak-to-valley height of the impression due to the particle indentation on the chrome-cobalt surface is assumed as an index of the induced damage. The calculated values range from 0.1,0.5 ,m for spherical particles of size ranging from 10,40 ,m. In the case of prismatic particles, the peak-to-valley height can reach 1.3 ,m and depends both on the size and width of the particle's free corner, indenting the chrome-cobalt. As an example, a sharp-edged particle of size 30 ,m can induce on the chrome-cobalt an impression with peak-to-valley height of 0.75 ,m, when embedded into the polyethylene with a free edge of 5 ,m facing the metallic surface. Negligible damage is induced, if a free edge of 7.5 ,m is indenting the counterface. Our findings offer new support to the hypothesis that microscopic third-body particles are capable of causing increased roughening of the femoral head and provide a quantitative evaluation of the phenomenon. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 436,448, 2001 [source] Kinetics and mechanistic analysis of caustic magnesia hydrationJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2004Sônia DF Rocha Abstract The kinetics of magnesia hydration to produce magnesium hydroxide is crucial for process design and control, and for the production of an Mg(OH)2 powder with desirable particle morphology. In this study, highly pure magnesia has been hydrated in a batch reactor. The effects of the following variables were evaluated experimentally: temperature (308,363 K), reaction time (0.5,5 h), initial slurry density (1,25%wt) and particle size in the ranges ,212 + 75 µm and ,45 + 38 µm. Experimental data indicate increasing magnesia hydration rates with increasing temperature, as expected. In addition, it has been observed that the hydration of magnesia increases significantly up to about 4,5%wt initial slurry density, stabilising afterwards. On the other hand, the reaction was almost unaffected when magnesia with different particle sizes were hydrated because of similar specific surface areas involved. A reaction mechanism to explain the oxide dissolution and the hydroxide precipitation has been proposed, assuming no significant change in the initial solids size and dissolution rate as the controlling step. The calculated activation energy value of 62.3 kJ mol,1 corroborates the mechanism proposed in this study and compares well with values previously reported in the literature. Copyright © 2004 Society of Chemical Industry [source] Cytotoxicity and apoptosis enhancement in brain tumor cells upon coadministration of paclitaxel and ceramide in nanoemulsion formulationsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2008Ankita Desai Abstract The objective of this study was to examine augmentation of therapeutic activity in human glioblastoma cells with combination of paclitaxel (PTX) and the apoptotic signaling molecule, C6 -ceramide (CER), when administered in novel oil-in-water nanoemulsions. The nanoemulsions were formulated with pine-nut oil, which has high concentrations of essential polyunsaturated fatty acid (PUFA). Drug-containing nanoemulsions were characterized for particle size, surface charge, and the particle morphology was examined with transmission electron microscopy (TEM). Epi-fluorescent microscopy was used to analyze nanoemulsion-encapsulated rhodamine-labeled PTX and NBD-labeled CER uptake and distribution in U-118 human glioblastoma cells. Cell viability was assessed with the MTS (formazan) assay, while apoptotic activity of PTX and CER was evaluated with caspase-3/7 activation and flow cytometry. Nanoemulsion formulations with the oil droplet size of approximately 200 nm in diameter were prepared with PTX, CER, and combination of the two agents. When administered to U-118 cells, significant enhancement in cytotoxicity was observed with combination of PTX and CER as compared to administration of individual agents. The increase in cytotoxicity correlated with enhancement in apoptotic activity in cells treated with combination of PTX and CER. The results of these studies show that oil-in-water nanoemulsions can be designed with combination therapy for enhancement of cytotoxic effect in brain tumor cells. In addition, PTX and CER can be used together to augment therapeutic activity, especially in aggressive tumor models such as glioblastoma. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:2745,2756, 2008 [source] Ultrasound-compacted indomethacin/polyvinylpyrrolidone systems: Effect of compaction process on particle morphology and dissolution behaviorJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2002Adamo Fini Abstract Indomethacin (IMC)/polyvinylpyrrolidone systems were prepared under different technological conditions, using co-evaporation, kneading, traditional, and ultrasound (US) compaction. The materials thus obtained were milled and sieved and the powders were analyzed by using scanning electron microscopy to evaluate the morphology of the final particles and the fractal dimension of the particle contour. In the case of US-treated particles, scanning electron micrographs suggest that IMC could have partially covered the excipient granule surface, which appears lustrous and smooth, whereas after co-evaporation, the particles display a stratified structure. The external color of the granules, the hot stage microscopy examination, and the absence of the melting peak of the drug in thermograms supports the idea that IMC converts into an amorphous form under US discharge. Each technological treatment performed on the binary mixtures increases the dissolution rate of the drug, with respect to the pure drug and the physical mixture, but to a lesser extent than US compaction. US compaction and co-evaporation produce comparable results in improving the release of the drug. Polyvinylpyrrolidone offers better results than ,-cyclodextrin in promoting the dissolution of IMC, when both systems are compacted under US. © 2002 Wiley-Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:1880,1890, 2002 [source] Effects of methylaluminoxane immobilization on silica on the performance of zirconocene catalysts in propylene polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2005Madri Smit Abstract Investigation of the characteristics and performance in propylene polymerization of silica-immobilized methylaluminoxane (MAO), in combination with a moderately and a highly isospecific zirconocene catalyst, has revealed that a simple impregnation of silica with MAO at ambient temperature is insufficient to obtain uniform distribution of MAO throughout the support particle. Homogeneous Al distribution throughout the support, giving increased catalyst activity, was achieved by a more rigorous impregnation of silica with MAO at elevated temperatures. The highest catalyst activities were obtained by precontacting the MAO with the zirconocene to generate the activated species before immobilization on silica. Polymer particle morphology was strongly dependent on the characteristics of the silica used for catalyst immobilization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2734-2748, 2005 [source] Nanoencapsulation of a hydrophobic compound by a miniemulsion polymerization processJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2004Yingwu Luo Abstract The nanoencapsulation of hydrophobic compounds by miniemulsion polymerization, a convenient one-step encapsulation technique for nanocapsules, was investigated in terms of the thermodynamics and kinetics. The encapsulation was achieved by polymerization inducing phase separation within minidroplets dispersed in an aqueous phase. Thermodynamic factors (the level and type of surfactant, the level of the hydrophilic comonomer, and the monomer/paraffin ratio), kinetic factors (the level of the crosslinking agent or chain-transfer agent), and nucleation modes were all found to have a great influence on the latex morphology. Specifically, for a styrene/paraffin system, there were optimum levels of sodium dodecyl sulfate (1.0 wt %), the hydrophilic comonomer (1.0 wt % methyl acrylate acid), and the chain-transfer agent (0.2 wt % n -dodecanethiol) for obtaining well-defined nanocapsules of paraffin with a styrene/paraffin ratio of 1:1. When the styrene/paraffin ratio was reduced, however, it was more difficult to achieve a fully encapsulated particle morphology. Homogeneous nucleation could compete with encapsulation, and this resulted in a pure polymer particle and a half-moon morphology. Conditions were also found under which complete encapsulation could be observed with a water-soluble initiator (potassium persulfate), contrary to certain reports. Replacing potassium persulfate with an oil-soluble initiator (2,2-azobisisobutyronitrile) had little influence on the morphology under those conditions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2145,2154, 2004 [source] Emulsion polymerization: From fundamental mechanisms to process developmentsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2004José M. Asua Abstract Emulsion polymers are "products by process" whose main properties are determined during polymerization. In this scenario of margins reduction, increasing competition, and public sensitivity to environmental issues, the challenge is to achieve an efficient production of high-quality materials in a consistent, safe, and environmentally friendly way. This highlight reviews the investigations carried out at The University of the Basque Country to develop a knowledge-based strategy to achieve these goals. First, the research in fundamental mechanisms is discussed. This includes studies in radical entry and exit, oil-soluble initiators, propagation-rate constants of acrylic monomers, processes involved in the formation of branched and crosslinked polymers, microstructure modification by postreaction operations, the formation of particle morphology, and reactive surfactants. The advanced mathematical models developed in the group are also reviewed. In the second part, the advances in process development (optimization, online monitoring and control, monomer removal, production of high-solids, low-viscosity latices, and process intensification) are presented. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1025,1041, 2004 [source] Spherical ordered mesoporous silicas and silica monoliths as stationary phases for liquid chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6 2006Anne Galarneau Abstract Ordered mesoporous silicas such as micelle-templated silicas (MTS) feature unique textural properties in addition to their high surface area (,1000 m2/g): narrow mesopore size distributions and controlled pore connectivity. These characteristics are highly relevant to chromatographic applications for resistance to mass transfer, which has never been studied in chromatography because of the absence of model materials such as MTS. Their synthesis is based on unique self-assembly processes between surfactants and silica. In order to take advantage of the perfectly adjustable texture of MTS in chromatographic applications, their particle morphology has to be tailored at the micrometer scale. We developed a synthesis strategy to control the particle morphology of MTS using the concept of pseudomorphic transformation. Pseudomorphism was recognized in the mineral world to gain a mineral that presents a morphology not related to its crystallographic symmetry group. Pseudomorphic transformations have been applied to amorphous spherical silica particles usually used in chromatography as stationary phases to produce MTS with the same morphology, using alkaline solution to dissolve progressively and locally silica and reprecipitate it around surfactant micelles into ordered MTS structures. Spherical beads of MTS with hexagonal and cubic symmetries have been synthesized and successfully used in HPLC in fast separation processes. MTS with a highly connected structure (cubic symmetry), uniform pores with a diameter larger than 6 nm in the form of particles of 5 ,m could compete with monolithic silica columns. Monolithic columns are receiving strong interest and represent a milestone in the area of fast separation. Their synthesis is a sol-gel process based on phase separation between silica and water, which is assisted by the presence of polymers. The control of the synthesis of monolithic silica has been systematically explored. Because of unresolved yet cladding problems to evaluate the resulting macromonoliths in HPLC, micromonoliths were synthesized into fused-silica capillaries and evaluated by nano-LC and CEC. Only CEC allows to gain high column efficiencies in fast separation processes. Capillary silica monolithic columns represent attractive alternatives for miniaturization processes (lab-on-a chip) using CEC. [source] Synthesis of PEDOT Nanoparticles and Vesicles by Dispersion Polymerization in Alcoholic MediaMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2006Muhammad Mumtaz Abstract Summary: The synthesis of PEDOT nanoparticles and vesicles by dispersion polymerization in a methanol/water mixture (3/2, v/v) is reported, using either ammonium persulfate or iron(III) p -toluenesulfonate as oxidants and , -EDOT-PEO as a reactive stabilizer. The influence of the oxidant as well as the , -EDOT-PEO molar mass and concentration on the core-shell particle morphology and conductivity properties have been investigated. PEDOT particles with conductivities up to 1.5,×,10,2 S,·,cm,1 have been obtained in high yield. TEM image of PEDOT vesicles prepared using PEO-based stabilizers of 25,000 g,·,mol,1 in water/methanol mixture (2:3 v/v) at room temperature using ammonium persulfate as an oxidant. [source] MAO-Free Activation of Metallocenes and other Single-Site Catalysts for Ethylene Polymerization using Spherical Supports based on MgCl2MACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2004John R. Severn Abstract Summary: Supports of type MgCl2/AlRn(OEt)3,n, obtained by reaction of AlR3 with adducts of MgCl2 and ethanol, have been shown to be effective for the immobilization and activation of [Cp2TiCl2] and other single-site olefin polymerization catalysts without the use of methylaluminoxane or a borate activator. Polyethylene with a spherical particle morphology and narrow molecular weight distribution was obtained. [source] Synthesis of Composite Polystyrene/Silica Nanoparticles via Precipitation and Emulsion Polymerization MethodsMACROMOLECULAR REACTION ENGINEERING, Issue 5 2010Katerina Kotti Abstract Polystyrene/silica composite nanoparticles were synthesized via precipitation and emulsion polymerization methods, in the presence of a basic co-monomer (e.g., 4-VP and 1-VID), and a colloidal aqueous silica solution. The effects of key process parameters, that is, solvent type, monomer/co-monomer volume ratio and total monomers concentration for precipitation polymerization, and reaction temperature, pH value, initial silica-sol concentration and initial monomer/co-monomer molar ratio for emulsifier-free emulsion polymerization on the particle morphology, silica content, and particle size distribution of the composite nanoparticles were experimentally investigated. Stable, spherical, and uniform in size composite nanoparticles were synthesized by both techniques. The average particle diameter varied from 108 to 182,nm for the emulsifier-free emulsion polymerization and from 400 to 800,nm for the precipitation polymerization, while the silica content was as high as 38.3,wt.-% for the former method and up to 15.5,wt.-% for the later. The synthesized composite polymer/silica particles were then electrolytically co-deposited with zinc on steel plates to improve the corrosion resistance of the metal's surface. [source] Design and Implementation of a Novel Quench Flow Reactor for the Study of Nascent Olefin PolymerisationMACROMOLECULAR REACTION ENGINEERING, Issue 2 2007Audrey Di Martino Abstract A novel stopped flow reactor system is described in the current work, along with the underlying design philosophy. While the concept of stopped flow technology is not recent, this system is the first to be designed with the objective of studying particle morphology, and to work at extremely short (40 ms) residence times. It is shown that traditional chemical engineering principles are required to properly design and operate this type of reactor, and that when correctly design, it is a very flexible tool for the study of nascent polymerisation of olefins. [source] Organic compound alteration during hypervelocity collection of carbonaceous materials in aerogelMETEORITICS & PLANETARY SCIENCE, Issue 1 2009M. K. SPENCER A major challenge in understanding the organic inventory of the returned comet dust is identifying, unambiguously, which organic molecules are indigenous to the cometary particles, which are produced from carbon contamination in the Stardust aerogel, and which are cometary organics that have been modified by heating during the particle capture process. Here it is shown that 1) alteration of cometary organic molecules along impact tracks in aerogel is highly dependent on the original particle morphology, and 2) organic molecules on test-shot terminal particles are mostly preserved. These conclusions are based on two-step laser mass spectrometry (L2MS) examinations of test shots with organic-laden particles (both tracks in aerogel and the terminal particles themselves). [source] Cryo-sectioning and chemical-fixing ultramicrotomy techniques for imaging rubber latex particle morphologyMICROSCOPY RESEARCH AND TECHNIQUE, Issue 2 2004Nadaraja Subramaniam Abstract Two methods adapted from biological microscopy are described for a new application in imaging the morphology of rubbery latex particles. In the first method, a drop of latex is frozen in liquid nitrogen, sectioned with a diamond knife and vapour-stained with osmium tetroxide, then viewed by transmission electron microscopy. When applied to latexes made by emulsion polymerization of methyl methacrylate in a natural rubber latex seed, inclusions are clearly visible. A chemical fixation method is then described for imaging the morphology of such rubbery latex particles. Glutaraldehyde is added to the latex, followed by osmium tetroxide. The sample is then dehydrated in ethanol, epoxy resin added, and the sample cured, ultramicrotomed, and imaged with transmission electron microscopy. An inclusion morphology is again clearly seen. Microsc. Res. Tech. 63:111,114, 2004. © 2004 Wiley-Liss, Inc. [source] Influence of Particle Morphology and Flow Conditions on the Dispersion Behavior of Fumed Silica in Silicone PolymersPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2004John Boyle Abstract The dispersion behavior of agglomerates of several grades of fumed silica in poly(dimethyl siloxane) liquids has been studied as a function of particle morphology and applied flow conditions. The effects of primary particle size and aggregate density and structure on cohesivity were probed through tensile and shear strength tests on particle compacts. These cohesivity tests indicated that the shear strength of particle compacts was two orders of magnitude higher than the tensile strength at the same overall packing density. Experiments carried out in both steady and time-varying simple-shear flows indicate that dispersion occurs through tensile failure. In the steady-shear experiments,enhanced dispersion was obtained at higher levels of applied stress and, at comparable levels of applied stress, dispersion was found to proceed faster at higher shear rates. Experiments conducted in time-varying flows further corroborated the results obtained in tensile cohesivity tests. Experiments in which the mean and maximum stresses in the time-varying flows were matched to the stresses produced in steady shear flows highlight the influence of flow dynamics on dispersion behavior. [source] Preparation of lithium indium oxide via a rheological phase route and its electrochemical characteristics in LiOH and Li2SO4 solutionsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010Guo-Qing Zhang Abstract Submicrometer-sized lithium indium oxide (LiInO2) powder via a rheological phase method using trilithium citrate tetra hydrate (C6H5Li3O7,·,4H2O) and indium oxide (In2O3) has been prepared in this work for the first time. The optimal pyrolyzing temperature range to prepare crystalline LiInO2 is between 650 and 900,°C, which was confirmed by thermal gravimetric and differential thermogravimetric analysis of the precursor and X-ray diffraction analysis. The pure phase LiInO2 sample obtained has a uniform particle morphology and submicrosize, which was observed by scanning electron microscopy. The electrochemical studies show that a new pair of cathodic and anodic peaks at 0.23 and 0.38,V (vs. saturated calomel electrode) was obviously observed from the cyclic voltammetry curve of LiInO2 in 1,M LiOH solution, indicating a battery characteristic of the material in this electrolyte. While in 1,M Li2SO4 solution, the sample presents a supercapacitive characteristic within the same potential range. The reasons for different electrochemical behaviors in these two electrolytes can be attributed to the fact that the reaction of lithium ion insertion/extraction into/out of a LiInO2 electrode takes place in the bulk material in LiOH electrolyte solution, whereas it takes place on the electrode/electrolyte interface for Li2SO4 electrolyte case. [source] Modeling particle inflation from poly(amic acid) powdered precursors.POLYMER ENGINEERING & SCIENCE, Issue 5 2007Morphological characteristics of polyimide microstructures obtained by solid-state powder foaming determine the geometric properties of the unit cell, in polyimide foams prepared by this process. Morphological analysis of precursor particles has shown that particle size and shape, as well as the presence of embedded microvoids, exert a strong influence on the final microstructure morphology. Of equal importance in the morphological development are processing conditions such as heating rate and primary blowing agent content in the particles, prior to thermal treatment. In the present paper, the first of two numerical schemes is presented. A numerical model has been developed to study the preliminary stages that lead to particle inflation. Based on this model, a parametric analysis is performed for pertinent governing parameters, with the purpose of determining their effect on the onset of particle inflation and the potential morphological characteristics of polyimide microstructures. It has been found that precursor particle morphology and nuclei density are the key parameters in determining the potential morphology of the microstructures, by limiting the number of bubbles that grow within each particle. POLYM. ENG. SCI., 47:560,571, 2007. © 2007 Society of Plastics Engineers. [source] | ||||||||||||||||||||||||||||