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Fabrication Conditions (fabrication + condition)
Selected AbstractsCapillary electrochromatography with monolithic silica column:,I.ELECTROPHORESIS, Issue 3 2003Preparation of silica monoliths having surface-bound octadecyl moieties, applications to the separation of neutral, charged species, their chromatographic characterization Abstract Monolithic silica columns with surface-bound octadecyl (C18) moieties have been prepared by a sol-gel process in 100 ,m ID fused-silica capillaries for reversed-phase capillary electrochromatography of neutral and charged species. The reaction conditions for the preparation of the C18-silica monoliths were optimized for maximum surface coverage with octadecyl moieties in order to maximize retention and selectivity toward neutral and charged solutes with a sufficiently strong electroosmotic flow (>,2 mm/s) to yield rapid analysis time. Furthermore, the effect of the pore-tailoring process on the silica monoliths was performed over a wide range of treatment time with 0.010 M ammonium hydroxide solution in order to determine the optimum time and conditions that yield mesopores of narrow pore size distribution that result in high separation efficiency. Under optimum column fabrication conditions and optimum mobile phase composition and flow velocity, the average separation efficiency reached 160,000 plates/m, a value comparable to that obtained on columns packed with 3 ,m C18-silica particles with the advantages of high permeability and virtually no bubble formation. The optimized monolithic C18-silica columns were evaluated for their retention properties toward neutral and charged analytes over a wide range of mobile phase compositions. A series of dimensionless retention parameters were evaluated and correlated to solute polarity and electromigration property. A dimensionless mobility modulus was introduced to describe charged solute migration and interaction behavior with the monolithic C18-silica in a counterflow regime during capillary electrochromatography (CEC )separations. The mobility moduli correlated well with the solute hydrophobic character and its charge-to-mass ratio. [source] The Influence of Tetracycline Loading on the Surface Morphology and Biocompatibility of Films Made from P(3HB) Microspheres,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Lydia Francis Tetracycline, an antibiotic used against a broad range of Gram positive and Gram negative bacteria was encapsulated in microspheres made of poly(3-hydroxybutyric acid) P(3HB), a microbial biodegradable polymer isolated from Bacillus cereus SPV. The drug loaded microspheres were prepared using an oil emulsion technique and compressed uniaxially to produce films. Although the same fabrication conditions were used for preparing the drug loaded and unloaded microspheres, the presence of the drug changed the surface morphology and roughness of the films. The surface morphology of the drug loaded films appeared uneven and coarser and the roughness, with an average root mean square value of 5.89,µm, was significantly higher than that of the unloaded film. The in vitro biocompatibility of the films was investigated using a human keratinocyte cell line (HaCaT) by comparing cell viability on the films to that on conventional tissue culture plastics. Both films appear to support cell growth but cell attachment and percentage cell viability were greater on the drug loaded films (32% of control) compared to the unloaded film (10% of control), possibly as a result of the non-uniform surface morphology and increased roughness of the drug loaded film. Thus, the above results illustrate that the drug loaded films, in addition to being a suitable matrix for drug delivery, represent an improved substrate for keratinocyte cell attachment. [source] Raman spectroscopy for spinline crystallinity measurements.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Abstract The original Doufas,McHugh two-phase microstructural/constitutive model for stress-induced crystallization is expanded to polyolefin systems and validated for its predictive capability of online Raman crystallinity and spinline tension data for two Dow homopolymer polypropylene resins. The material parameters,inputs to the model,are obtained from laboratory-scale material characterization data, that is, oscillatory dynamic shear, rheotens (melt extensional rheology), and differential scanning calorimetry data. The same set of two stress-induced crystallization material/molecular parameters are capable of predicting the crystallinity profiles along the spinline and fiber tension very well overall for a variety of industrial fabrication conditions. The model is capable of predicting the freeze point, which is shown, for the first time, to correlate very well with the measured stick point (i.e., the point in the spinline at which the fiber bundle converts from a solid-like state to a liquid-like state and sticks to a solid object such as a glass rod). The model quantitatively captures the effects of the take-up speed, throughput, and melt flow rate on the crystallization rate of polypropylene due to stress-induced crystallization effects. This validated modeling approach has been used to guide fiber spinning for rapid product development. The original Doufas,McHugh stress-induced crystallization model is shown to be numerically robust for the simulation of steady polypropylene melt spinning over a wide range of processing conditions without issues of discontinuities due to the onset of the two-phase constitutive formulation downstream of the die face, at which crystallization more realistically begins. Because of the capturing of the physics of polypropylene fiber spinning and the very good model predictive power, the approximations of the original Doufas,McHugh model are asserted to be reasonable. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Criterion for the Avoidance of Edge Cracking in Layered SystemsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2004M. Y. He When fabricating multilayers with brittle constituents, a prevalent design strategy is to choose fabrication conditions and thermal expansion coefficients that impose in-plane compression on the brittle layers. In such designs, a small zone of out-of-plane tension is induced at the edges that can cause cracks to form and extend, especially along the midplane. The associated stresses and energy release rates have been analyzed, revealing a fail-safe criterion, attributed to the existence of a maximum possible energy release rate, Gmax. Equating this maximum to the toughness defines a fail-safe parameter expressing the influence of the layer thickness, the misfit stress, and the toughness. When fail-safe designs cannot be realized, thin interlayers can be interposed in a manner that diminishes Gmax, broadening accessibility. The roles of misfit stress and interlayer thickness in attaining this condition are derived. [source] Preparation and Growth Mechanism of Molybdenum Trioxide WhiskerJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2002Jianqiang Li A new whisker, ,-MoO3, was fabricated via molybdenum thread oxidation at 973, 1023, and 1173 K. Various morphologies of the whiskers, such as flakelike, platelike, and needlelike, were observed under different fabrication conditions. The lateral surfaces of the whiskers were close-packed (010) plane, and the growth direction was (001), which related to the unique layered structure of the ,-MoO3 crystal. Growth of the MoO3 whiskers was attributed to a vapor-liquid-solid (VLS) mechanism at 1023 and 1173 K, whereas, at 973 K, growth was attributed to a vapor-liquid (VL) mechanism. [source] Magnetic properties of FeCuNbSiB nanocrystalline alloy powder cores produced from atomized powders by cold pressingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004Gwang-Bo Choi Abstract Powder cores were produced from gas- and water-atomized powders by cold pressing at a pressure of 1.5 GPa. Structure, morphology and thermal stability analyses of the powders were carried out. The magnetic properties of the cores were examined at high frequency. Gas-atomized powder cores exhibit excellent high-frequency characteristics, which are a stable permeability up to 50 MHz, a quality factor of maximum value 95 at a frequency of 400 kHz and a core loss of 650 mW/cm3 at f = 50 kHz and Bm = 0.1 T. It is considered that the excellent magnetic properties of FeCuNbSiB powder cores are due to the fact that atomized powders with nanocrystalline structure show good softness in magnetic properties and important fabrication conditions like an insulating layer and extremely high compacting pressure are well controlled. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preparation and properties of ionically cross-linked chitosan nanoparticlesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2009Hui Liu Abstract Chitosan nanoparticles were fabricated by a method of tripolyphosphate (TPP) cross-linking. The influence of fabrication conditions on the physical properties and drug loading and release properties was investigated by transmission electron microscopy (TEM), dynamic light scattering (DLS), and UV,vis spectroscopy. The nanoparticles could be prepared only within a zone of appropriate chitosan and TPP concentrations. The particle size and surface zeta potential can be manipulated by variation of the fabrication conditions such as chitosan/TPP ratio and concentration, solution pH and salt addition. TEM observation revealed a core,shell structure for the as-prepared nanoparticles, but a filled structure for the ciprofloxacin (CH) loaded particles. Results show that the chitosan nanoparticles were rather stable and no cytotoxicity of the chitosan nanoparticles was found in an in vitro cell culture experiment. Loading and release of CH can be modulated by the environmental factors such as solution pH and medium quality. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||