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Synthesis Parameters (synthesis + parameter)
Selected AbstractsHybrid Nanofiber Growth: One-Pot Synthesis of Functional Helicoidal Hybrid Organic,Inorganic Nanofibers with Periodically Organized Mesoporosity (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Mater. Luminescent nanofibers are grown with controlled alignment of twisted nanochannels, as described by K. Valle and co-workers on page 2896. Tuning of the main synthesis parameters (sol-gel conditions, temperatures, choice of surfactants and inorganic precursors) allows the fine control of morphology, porosity-architecture, and organic chemical functionalization in order to prepare useful functional nanofibers. [source] One-Pot Synthesis of Functional Helicoidal Hybrid Organic,Inorganic Nanofibers with Periodically Organized MesoporosityADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Frédéric Rambaud Abstract The one-pot synthesis and properties of multifunctional hybrid mesoporous organosilica fibers with helical shapes are described. These hybrid mesoporous fibers are prepared without chiral elements and functionalized with a large variety of organic R functions (R,=,alkylthiols, phenylsulfonates, alkylphosphonates, dansyl, aminopropyl, fluoroalkyl, etc.). The resulting nanomaterials are thoroughly characterized by a variety of techniques. The use of a synergetic combination of achiral molecules as co-directing structuring agents, a surfactant, and an organofunctional silica precursor R-Si(OR)3 allows, via carefully tuning of the main synthesis parameters and processing conditions, to control the shape, which is the anisotropic factor, of the hybrid nanofibers. The functionalization of the hybrid materials with fluorescent molecules (dansyl) and gold nanoparticles opens possibilities for sensor and catalytic applications, respectively. Moreover, these hybrid nanofibers can be easily transferred in organic solvents or in a "green" solvent such as water to make stable colloidal dispersions. This tunable functionality of nanofibers also allows their transferability into a variety of polymeric hosts (PVDF, PVBu, and PVP) allowing the formation of functional homogeneous nanocomposite hybrid membranes. [source] Ordered Mesoporous In2O3: Synthesis by Structure Replication and Application as a Methane Gas SensorADVANCED FUNCTIONAL MATERIALS, Issue 4 2009Thomas Waitz Abstract The synthesis and characterization of ordered mesoporous In2O3 materials by structure replication from hexagonal mesoporous SBA-15 silica and cubic KIT-6 silica is presented. Variation of the synthesis parameters allows for different pore sizes and pore wall thicknesses in the products. The In2O3 samples turn out to be stable up to temperatures between 450,°C and 650,°C; such high thermal stability is necessary for their application as gas sensors. Test measurements show a high sensitivity to methane gas in concentrations relevant for explosion prevention. The sensitivity is shown to be correlated not only with the surface-to-volume ratio, but also with the nanoscopic structural properties of the materials. [source] Confinement of Thermoresponsive Hydrogels in Nanostructured Porous Silicon Dioxide Templates,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2007E. Segal Abstract A thermoresponsive hydrogel, poly(N -isopropylacrylamide) (poly(NIPAM)), is synthesized in,situ within an oxidized porous Si template, and the nanocomposite material is characterized. Infiltration of the hydrogel into the interconnecting nanoscale pores of the porous SiO2 host is confirmed by scanning electron microscopy. The optical reflectivity spectrum of the nanocomposite hybrid displays Fabry,Pérot fringes characteristic of thin film interference, enabling direct, real-time observation of the volume phase transition of the confined poly(NIPAM) hydrogel. Reversible optical reflectivity changes are observed to correlate with the temperature-dependent volume phase transition of the hydrogel, providing a new means of studying nanoscale confinement of responsive hydrogels. The confined hydrogel displays a swelling and shrinking response to changes in temperature that is significantly faster than that of the bulk hydrogel. The porosity and pore size of the SiO2 template, which are precisely controlled by the electrochemical synthesis parameters, strongly influence the extent and rate of changes in the reflectivity spectrum of the nanocomposite. The observed optical response is ascribed to changes in both the mechanical and the dielectric properties of the nanocomposite. [source] Modeling and synthesis of the interdigital/stub composite right/left-handed artificial transmission lineINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2009R. Siragusa Abstract An efficient design procedure, including both analysis and synthesis, is proposed for Composite Right/Left Handed (CRLH) interdigital/stub structures. Improved models are developed for both the interdigital capacitor and the shorted stub inductor including its ground via hole. Subsequent optimal formulas are recommended to model these components with their parasitic effects. The models and formulas are verified by both full-wave and experimental results. A CAD program with a friendly GUI, available online, is provided and its operation is described in details. This program allows a very fast design of the CRLH structure, and its synthesis parameters are proven very accurate without any full-wave optimization. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009. [source] Lipase-catalyzed ethanolysis of soybean oil in a solvent-free system using central composite design and response surface methodologyJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2008Rafael Costa Rodrigues Abstract BACKGROUND: In this work we describe the synthesis of ethyl esters, commonly known as biodiesel, using refined soybean oil and ethanol in a solvent-free system catalyzed by lipase from Thermomyces lanuginosus. Central composite design and response surface methodology (RSM) were employed to optimize the biodiesel synthesis parameters, which were: reaction time, temperature, substrate molar ratio, enzyme content, and added water, measured as percentage of yield conversion. RESULTS: The optimal conditions obtained were: temperature, 31.5 °C; reaction time, 7 h; substrate molar ratio, 7.5:1 ethanol:soybean oil; enzyme content, 15% (g enzyme g,1 oil); added water, 4% (g water g,1 oil). The experimental yield conversion obtained under these conditions was 96%, which is very close to the maximum predicted value of 94.4%. The reaction time-course at the optimal values indicated that 5 h was necessary to obtain high yield conversions. CONCLUSION: A high yield conversion was obtained under the optimized conditions, with relative low enzyme content and short time. Comparison of predicted and experimental values showed good correspondence, implying that the empirical model derived from RSM can be used to adequately describe the relationship between the reaction parameters and the response (yield conversion) in lipase-catalyzed biodiesel synthesis. Copyright © 2008 Society of Chemical Industry [source] Optimisation of kojic acid monolaurate synthesis with lipase PS from Pseudomonas cepaciaJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 6 2002Chee-Shan Chen Abstract To improve the instability of kojic acid in food and cosmetic use, the esterification of kojic acid catalysed by lipase from Pseudomonas cepacia (Amano PS) to synthesise kojic acid monolaurate (KAML) was investigated in this study. Response surface methodology (RSM) with a five-level/five-factor central composite rotatable design (CCRD) was employed to evaluate the effects of synthesis parameters such as reaction time (8,24,h), temperature (35 55,°C), enzyme amount (10,50%), substrate molar ratio of lauric acid to kojic acid (1:1,3:1) and added water content (0,20%) on the percentage molar conversion to KAML by direct esterification. Reaction time and added water content were the most important variables, while substrate molar ratio had less effect on percentage molar conversion. Based on canonical analysis and ridge maximum analysis, optimal synthesis conditions were reaction time 19,h, temperature 44,°C, enzyme amount 38%, substrate molar ratio 2:1 and added water content 10%. The predicted value was 85% and the actual experimental value 82% molar conversion. © 2002 Society of Chemical Industry [source] Kinetic Modeling of Thiol-Ene Reactions with Both Step and Chain Growth AspectsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4 2005Oguz Okay Abstract Summary: A kinetic model is presented for thiol-ene cross-linking photopolymerizations including the allowance for chain growth reaction of the ene, i.e., homopolymerization. The kinetic model is based on a description of the average chain lengths derived from differential equations of the type of Smoluchowski coagulation equations. The method of moments was applied to obtain average properties of thiol-ene reaction systems. The model predicts the molecular weight distribution of active and inactive species in the pre-gel regime of thiol-enes, as well as the gel points depending on the synthesis parameters. It is shown that, when no homopolymerization is allowed, the average molecular weights and the gel point conversion are given by the typical equations valid for the step-growth polymerization. Increasing the extent of homopolymerization also increases the average molecular weights and shifts the gel point toward lower conversions and shorter reaction times. It is also shown that the ratio of thiyl radical propagation to the chain transfer kinetic parameter (kp1/ktr) affects the gelation time, tcr. Gelation occurs earlier as the kp1/ktr ratio is increased due to the predominant attack of thiyl radicals on the vinyl groups and formation of more stable carbon radicals. The gel point in thiol-ene reactions is also found to be very sensitive to the extent of cyclization, particularly, if the monomer functionalities are low. Number-average chain length of carbon radicals (solid curves) and thiyl radicals (dashed curves) plotted against the vinyl group conversion, xM, during thiol-ene polymerization. Calculations were for six different kp/ktr ratios. [source] Morphology studies of doped polyaniline micro/nanocomposites containing TiO2 nanoparticles and Fe3O4 microparticlesPOLYMER COMPOSITES, Issue 7 2009Sook-Wai Phang To produce polyaniline (PAni) nanodevices that display excellent microwave absorbing behaviors, novel hexanoic acid-doped PAni micro/nanocomposites containing TiO2 nanoparticles and Fe3O4 microparticles (PAni/HA/TiO2/Fe3O4) were prepared by template-free method, particularly to improve the dielectric and magnetic property of PAni. PAni/HA/TiO2/Fe3O4 synthesized at different polymerization temperatures and polymerization time by various TiO2 and Fe3O4 contents, and particles size of TiO2 were prepared. The aim of this research is to investigate the effect of synthesis condition on the morphology behaviors of nanorods/tubes. The resulted nanorods/tubes indicated that PAni micro/nanocomposites exhibited polymerization through elongation. PAni micro/nanocomposites synthesized at 0°C resulted in large amounts of nanorods/tubes compared with those synthesized at subzero temperature and above 0°C. PAni/HA/TiO2 and PAni/HA/TiO2/Fe3O4 synthesized using TiO2 with diameter (particles size) 180 nm resulted in large amounts of nanorods/tubes (diameter nanorods/tubes = 80,140 nm) compared with those synthesized using TiO2 with diameter of 30 and 6 nm. Increasing TiO2 and Fe3O4 content above 10% will significantly reduce the amount of nanorods/tubes. In conclusion, synthesis parameters mentioned above are the significant factors that might affect the morphology behaviors of PAni nanostructures. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] | |||||||||||||