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Stable Suspensions (stable + suspension)
Selected AbstractsRapid Expansion from Supercritical to Aqueous Solution to Produce Submicron Suspensions of Water-Insoluble DrugsBIOTECHNOLOGY PROGRESS, Issue 3 2000Timothy J. Young Stable suspensions of submicron particles of cyclosporine, a water-insoluble drug, have been produced by rapid expansion from supercritical to aqueous solution (RESAS). To minimize growth of the cyclosporine particles, which would otherwise occur in the free jet expansion, the solution was sprayed into an aqueous Tween-80 (Polysorbate-80) solution. Steric stabilization by the surfactant impedes particle growth and agglomeration. The particles were an order of magnitude smaller than those produced by RESS into air without the surfactant solution. Concentrations as high as 38 mg/mL for 400,700 nm particles were achieved in a 5.0% (w/w) Tween-80 solution. [source] Single-Walled Carbon Nanotube/Trititanate Nanotube Composite Fibers,ADVANCED ENGINEERING MATERIALS, Issue 7 2009Chonlada Dechakiatkrai For the first time, single-walled carbon nanotubes were dispersed with titanate nanotubes using bio-polymers. Direct injection (wet spinning) of the stable suspension of H2Ti3O7 and SWNTs into coagulation baths produced fibers. The mechanical and electrical properties along with surface morphology and electrochemistry of the resulting fibers were investigated. The presence of SWNTs clearly improved the mechanical and electrical properties of the composite fibers compared with H2Ti3O7 alone. [source] Transparent Polycrystalline Alumina Ceramic with Sub-Micrometre Microstructure by Means of Electrophoretic DepositionMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 4 2006A. Braun Abstract The optical quality attainable in coarse-grained polycrystalline alumina is severely limited by grain-boundary scattering, which is inherent to non-cubic materials. The optical properties of sub-micrometre polycrystalline alumina are of growing interest triggered by the fact that a decrease in the grain sizes of the final sintered material yields an improvement in the optical quality while the scattering mechanism changes as the grain size becomes comparable with the wavelength of light. To achieve transparent alumina ceramics with a fine-grained microstructure, however, porosity and other defects must be avoided. This necessitates the optimization of processing and sintering procedures. Electrophoretic deposition (EPD) is a colloidal process in which ceramic bodies are directly shaped from a stable suspension by application of an electric field. Electrophoretic deposition enables the formation of homogeneous, uniform green microstructures with high density, which can be sintered to transparency. It is a simple and precise technique to synthesize not only monoliths, but also composites with complex geometries [1]. Alumina green bodies were deposited from stabilized aqueous suspensions with and without doping. Green alumina compacts were evaluated based on their pore size distribution and density. Densification behaviour was characterized by dilatometric studies conducted at constant heating rate. Samples were sintered at different temperatures with subsequent post-densification by hot isostatic pressing. Transparency was evaluated by means of spectroscopic measurements. The measured in-line transmission of the samples at 645 nm was more than 50,% and that is 58,% of the value of sapphire. The influence of dopings on transparency was investigated. The mechanical properties of the samples were tested. [source] Single-walled carbon nanotubes modified by PFO: An optical absorption and Raman spectroscopic investigationPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009P. Lukaszczuk Abstract In this contribution, we present preliminary results from an optical absorption and resonance Raman spectroscopic investigation on single-walled carbon nanotubes (SWCNT) functionalized by poly(9,9-dioctylfluorenyl-2,7-diyl)- co -bithiophene (PFO-BTP). A route for a stable suspension of SWCNT in a solution of fluorine-base copolymer is shown. Additionally, the detailed analysis of the supernatant and sediment after centrifugation of the functionalized sample is given. The resonance Raman and optical absorption spectroscopic data suggest that selective wrapping of the carbon nanotubes by PFO occurs. Additionally, one can see that the abundance of SWCNT in the supernatant in a bulk sample increased by a factor of 2. [source] Recent progress in the use of soluble ionic polymers as pseudostationary phases for electrokinetic chromatographyELECTROPHORESIS, Issue 23-24 2004Christopher P. Palmer Abstract This review concerns the development, characterization, and application of soluble ionic polymeric materials as pseudostationary phases for electrokinetic chromatography since 2002. Cationic polymers, anionic siloxanes, polymerized surfactants (micelle polymers), and chiral polymers are considered. The use of stable suspensions of polymer nanoparticles in electrokinetic chromatography is also reviewed. [source] A Facile Synthesis and Characterization of Monodisperse Spherical Pigment Particles with a Core/Shell Structure,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2007C. Lin Abstract In this paper, a facile sol,gel process for producing monodisperse, spherical, and nonaggregated pigment particles with a core/shell structure is reported. Spherical silica particles (245 and 385,nm in diameter) and Cr2O3, ,-Fe2O3, ZnCo2O4, CuFeCrO4, MgFe2O4, and CoAl2O4 pigments are selected as cores and shells, respectively. The obtained core/shell-structured pigment samples, denoted as SiO2@Cr2O3 (green), SiO2@,-Fe2O3 (red), SiO2@MgFe2O4 (brown), SiO2@ZnCo2O4 (dark green), SiO2@CoAl2O4 (blue), and SiO2@CuFeCrO4 (black), are well characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and UV-vis diffuse reflection, as well as by investigating the magnetic properties. The results of XRD and high-resolution TEM (HRTEM) demonstrate that the pigment shells crystallize well on the surface of SiO2 particles. The thickness of the pigment shell can be tuned by the number of coatings, to some extent. These pigment particles can be well dispersed in some solvents (such as glycol) to form relatively more stable suspensions than the commercial products. Apart from the color characteristics, some of pigments like SiO2@Cr2O3, SiO2@MgFe2O4, and SiO2@CuFeCrO4 also show magnetic properties with coercivities of 1098,Oe (5,K), 648,Oe (5,K), and 91,Oe (298,K), respectively. [source] Design and scale-up of chemical reactors for nanoparticle precipitationAICHE JOURNAL, Issue 5 2006Daniele L. Marchisio Abstract In recent years there has been a growing interest in production on an industrial scale of particles with size in the sub-micron range (40-200 nm). This can be done by controlling particle formation in order to nucleate very small particles and by tailoring the particle surface in order to avoid particle aggregation and produce stable suspensions. In this work we focus on the role of turbulent mixing on particle formation in confined impinging jet reactors. In particular, we show how computational fluid dynamics and simple precipitation models could be used to derive scale-up criteria for the production of nanoparticles. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Towards an understanding of adsorption behaviour in non-aqueous systems: adsorption of poly(vinyl pyrrolidone) and poly(ethylene glycol) onto silica from 2H, 3H-perfluoropentaneJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 11 2005Alison Paul The adsorption behaviour of low molecular weight poly(ethylene glycol) (PEG 600) and poly(vinyl pyrrolidone) (PVP K25) to silica particles has been investigated at room temperature (21°C) in the partially fluorinated solvent 2H,3H-perfluoropentane (HPFP). PVP (absorbed amount, , = 12 mgg,1) was found to adsorb more strongly than PEG (, = 4 mgg,1). Both of these values were higher than observed in water. In a further distinction to the aqueous case, where PVP displaces PEG from the interface, no competitive adsorption effects were observed between these two polymers in HPFP, with the adsorbed amounts of each polymer being unchanged by the presence of the other. The stability of silica suspensions in HPFP was primarily dependent on the presence of PVP; PEG/silica systems were unstable, but PVP/silica and PEG/PVP/silica systems formed stable suspensions. All suspensions were destabilized by the addition of small (0.15 wt%) amounts of water. The observations made in this work would point to a flocculation phenomenon due to the addition of water, and not Ostwald ripening. The mechanism of this destabilization is likely to be water acting as a flocculation bridge between particles. [source] Dispersing silicon nanoparticles in a stirred media mill , investigating the evolution of morphology, structure and oxide formationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2007A. Reindl Abstract Silicon nanoparticles were dispersed for 24 hours in 1-butanol using a stirred media mill. Via this process intrinsically stable suspensions (in regard to aggregation) of Si nanoparticles were produced after 6 hours of dispersing. The evolution of morphology, particle size and structure was investigated by dynamic light scattering, X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy as a function of dispersing time. The average crystallite size decreased from about 18 nm down to about 10 nm within 24 hours of milling as determined by X-ray diffraction and Raman scattering measurements. In addition careful analysis of the Raman spectra revealed a decrease of the crystalline volume fraction from 75% down to 24% and a corresponding increase of the amorphous phase. The microstructural development with varying crystallite size and crystalline volume fraction was directly confirmed by transmission electron microscopy measurements. Elemental analysis showed an increase of oxygen content that was directly proportional to the increase in specific surface area of the silicon nanoparticles during the dispersing process. The surface chemistry of the Si nanoparticles was analyzed by diffuse reflectance infrared Fourier transform spectroscopy that indicated vibrational bands of HSi,Si3,xOx, SiOx, and residual 1-butanol. The final product of the dispersing process seems to be a two-phase mixture of amorphous Si and Si nanocrystallites covered with SiOx on the surface. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||