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Preparation Conditions (preparation + condition)
Selected AbstractsA New Way to Improve Glass-Forming Ability by Controlling the Preparation Conditions of Bulk Metallic GlassADVANCED ENGINEERING MATERIALS, Issue 3 2010Jie Mao Abstract The effects of mold preheating temperature on the glass-forming ability of Zr64.9Al7.9Ni10.7Cu16.5 and Zr47Cu37.5Ag7.5Al8 alloys are investigated using traditional copper mold casting. It is found that there exists an optimum mold temperature for glass-forming alloy systems. For the two Zr-based alloy systems studied the optimum mold temperature is 353,K. This is explained from the perspectives of heat transfer efficiency and the wettability between liquid alloy and copper mold. [source] Optimizing Preparation Conditions for Heat-denatured Whey Protein Solutions to be Used as Cold-gelling IngredientsJOURNAL OF FOOD SCIENCE, Issue 2 2000C.M. Bryant ABSTRACT: Heat-denatured whey protein solutions are used to make ingredients that gel at low temperatures. This study examines the influence of holding temperature (65 to 90°C), holding time (5 to 30 min), protein concentration (2 to 12 wt%) and pH (3 to 8) on the rheology and appearance of heat-denatured whey protein solutions. The optimum preparation conditions required to produce non-gelled transparent solutions of heat-denatured proteins were established. The rate of cold-gelation after the addition of 200 mM NaCl to the heat-denatured whey protein solutions increased as their initial viscosity increased. It was possible to produce gels with different cold-gelling characteristics by altering the thermal preparation conditions. [source] ,-Gallium Oxide as Oxygen Gas Sensors at a High TemperatureJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007Marilena Bartic Resistive oxygen sensors based on gallium oxide were fabricated in order to analyze their sensing performances (as sensitivity, response, and recovery time) in an oxygen atmosphere at 1000°C. We prepared three types of sensors using a ,-Ga2O3 single crystal in a sandwich structure with Pt pad electrodes and ,-Ga2O3 polycrystalline thin films deposited by using both the sputtering technique and the chemical solution deposition method. For thin-film sensors, Pt interdigital electrodes were deposited on the surface of the films using the lift-off method. X-ray diffraction and atomic force microscopy investigations were performed to compare the structure and surface morphology of the samples. We achieved a response time of 10 s at 1000°C, while the sensitivity was 1.03 for the single crystal and 1.35,1.45 for thin films. The sensing properties depend on the preparation condition of Ga2O3 devices. [source] Comparison of three cytologic preparation methods and immunocytochemistries to distinguish adenocarcinoma cells from reactive mesothelial cells in serous effusionDIAGNOSTIC CYTOPATHOLOGY, Issue 1 2006(I.A.C.), Junko Ueda Ph.D. Abstract We assessed whether a panel of seven antibodies is useful in the differentiation of adenocarcinoma cells (ACCs) from reactive mesothelial cells (RMCs) in effusion samples and to determine optimal specimen preparation conditions for immunocytochemical analysis of effusion samples. Immunocytochemistry (ICC) was performed on three types of effusion preparations from the same effusion specimens: ethanol-fixed smears, ethanol-fixed cell -blocks, and formalin-fixed cell-blocks. Commercially available antibodies MOC-31, Ber-EP4, CA19-9, CEA, EMA, CA125, and HBME-1 were tested on RMCs from four samples of various etiology and 15 samples of adenocarcinoma from various primary sites. Ethanol-fixed smears showed strong immunoreactivity to all antibodies tested. The immunoreactivity of ethanol-fixed and formalin-fixed cell-blocks was significantly lower with all antibodies except CA19-9. Smear preparations are more sensitive than cell-blocks for immunocytochemical study. A panel of antibodies MOC-31, Ber-EP4, CA19-9, and CEA appears to be suitable to distinguish between ACCs and RMCs. Diagn. Cytopathol. 2006;34:6,10. © 2005 Wiley-Liss, Inc. [source] Parameters governing reproducibility of flow properties of porous monoliths photopatterned within microfluidic channelsELECTROPHORESIS, Issue 14 2010Mei He Abstract We report the patternability as well as the reproducibility and stability of flow resistance of polymer monolithic beds photopatterned within microfluidic channels as a function of initial reagent composition and preparation conditions. 2-Hydroxyethyl methacrylate and ethylene dimethacrylate-based polymer monoliths were selectively photopatterned within microchannels and their flow resistance was evaluated using a photobleaching, TOF linear flow rate measurement method developed in our lab. This measurement technique was found to be significantly more informative for columns formed in microfluidic channels compared with bulk monolith characterization by mercury intrusion porosimetry. 1-Octanol was determined to provide sharp bed edge formation and relatively low flow resistance by photopatterning relative to other porogenic solvents. Compared with literature formulations which did not achieve good flow stability and reproducibility from batch to batch, using 2-hydroxyethyl methacrylate, ethylene dimethacrylate and 1-octanol as porogenic solvents, less than 4% RSD was achieved in flow stability over 7 days for monoliths prepared with 60,80% crosslinker(monomer+crosslinker) ratio. Column-to-column variation of 5% RSD was obtained in this composition range. These results demonstrate that photopatterning of uniform polymer monolithic beds, which is critical for applications in multiplexed microfluidic systems, requires careful attention to the parameters that affect reproducibility, specifically the porogenic solvent choice and the crosslinker to monomer ratio. [source] Current-Voltage Characterisation of Monolayer-Supported Au-Nanoclusters by Scanning Tunnelling Microscopy under Ambient ConditionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2005Volker Jacobsen Abstract The current-voltage characteristics of a double-tunnel junction based on a gold crystallite with a diameter of ca. 2 nm, separated from a gold surface by ca. 1 nm was investigated by scanning tunnelling microscopy. The sample architecture was built by attaching gold nanoparticles covered with 2-mercaptosuccinic acid to an atomically flat gold surface which was covered by a self-assembled monolayer (SAM) of 6-amino-1-hexanethiol. Surface plasmon and infrared spectroscopy as well as STM imaging were employed to identify suitable preparation conditions and prove the existence of the desired architecture. No reproducible steps in the current-voltage characteristics are observed on this system under ambient conditions. Nonetheless, a sound signature for tunnelling through the double-tunnel junction is established by a quantitative fit of the averaged experimental data to a theoretical model of a single-tunnel junction. Firstly, the current on the particle is strongly reduced at low absolute external voltage and secondly the current voltage characteristics are asymmetric. Since both deviations from theory are absent in reference experiments on the bare monolayer, they may serve as a robust signature for double-tunnel junctions and open the door to the investigation of single-electron tunnelling under ambient conditions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Preparation-Condition Dependence of Hybrid SiO2 -Coated CdTe Nanocrystals with Intense and Tunable PhotoluminescenceADVANCED FUNCTIONAL MATERIALS, Issue 8 2010Ping Yang Abstract When aqueously prepared CdTe nanocrystals (NCs) are coated with a SiO2 shell containing Cd ions and a sulfur source, they show a drastic increase in photoluminescence (PL) efficiency with a significant red shift and spectral narrowing after reflux. This is ascribed to the creation of a hybrid structure characterized by the formation of CdS-like clusters in the vicinity of the NCs in the SiO2 shell. Since these clusters are close to the NCs, their effective size increases to reduce the quantum size effect. The dependences of the PL properties on the preparation conditions are systematically investigated. The PL efficiency increases from 28% to 80% in the best case with a red shift of 80,nm. The PL behaviors differ from those of normal CdTe NCs and include less temperature quenching and longer PL lifetime. The SiO2 coating enables bioconjugation with IgG without deterioration of PL efficiency, making hybrid NCs amenable for bioapplication. [source] Effects of Structural Variation on the Photocatalytic Performance of Hydrothermally Synthesized BiVO4,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2006J. Yu Abstract Highly crystalline monoclinic scheelite BiVO4 powders are synthesized from aqueous Bi(NO3)3 and NH4VO3 solutions over a wide range of pH by a hydrothermal process. BiVO4 powders with various morphologies, surface textures, and grain shapes are selectively synthesized by adjusting the pH. The dependence of the Raman peak position and intensity on the synthesis conditions indicates that the symmetry distortions in the local structure of the synthesized BiVO4 are affected by the preparation conditions. These variations in the local structure result in the modification of the electronic structure of BiVO4, which results in a blue-shift in the UV-vis absorption spectrum of hydrothermally synthesized BiVO4 in comparison with a well-crystallized sample prepared by homogeneous coprecipitation. The photocatalytic activities for O2 evolution from an aqueous AgNO3 solution under visible-light irradiation are strongly dependent on the pH used in the synthesis. The differences in the photocatalytic activities between BiVO4 samples prepared under various conditions is attributed to the degree of structural distortion, leading to differences in the mobility of photogenerated holes formed in the valence band, which consists of Bi,6s and O,2p orbitals. [source] Effect of the preparation conditions on the permeation of ultrahigh-molecular-weight polyethylene/silicon dioxide hybrid membranesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Nana Li Abstract Porous ultrahigh-molecular-weight polyethylene/SiO2 membranes were prepared by thermally induced phase separation (TIPS) with white mineral oil as the diluent and SiO2 as an additive. Influential factors, including extraction method, SiO2 content, and cooling rate, were investigated. The results suggest that the both porosity and pure water flux of the membranes by extraction of the solvent naphtha in the tension state with alcohol were the best among our research. With increasing SiO2 content, the porosity, pure water flux, and pore diameter increased. However, with excessive SiO2 content, defects formed easily. Moreover, SiO2 improved the pressure resistance of the membranes. The cooling rate directly effected the crystal structure. A slow cooling rate was good for crystal growth and the integration of the diluent. Therefore, the porosity, pure water flux, and bubble-point pore diameter increased with decreasing cooling rate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Examination of membrane protein expression in Paracoccus denitrificans by two-dimensional gel electrophoresisJOURNAL OF BASIC MICROBIOLOGY, Issue 1 2004Pavel Bouchal The well-known metabolic versatility of the soil bacterium Paracoccus denitrificans poses a challenge for modern proteomic approaches. We describe here improved preparation conditions that allow good separation and quantitative analyses of hundreds of membrane or periplasmic proteins. To illustrate this optimized procedure, the results of a screening for membrane proteins associated predominantly with aerobic or anaerobic (denitrifying) modes of growth are presented. [source] Study of the preparation and composition of the metallic function for the selective hydrogenation of CO2 to gasoline over bifunctional catalysts,JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2-3 2003Javier Ereña Abstract Bifunctional catalysts for the transformation of carbon dioxide and hydrogen into gasoline have been prepared by conventional and novel processes and characterized by measurement of BET surface area and volume and distribution of pores, and by X-ray diffraction, FTIR spectroscopy and X-ray fluorescence. The effects of the preparation conditions and of the atomic ratios between the metals on the structure and on the properties of the catalysts were studied. © 2003 Society of Chemical Industry [source] Optimizing Preparation Conditions for Heat-denatured Whey Protein Solutions to be Used as Cold-gelling IngredientsJOURNAL OF FOOD SCIENCE, Issue 2 2000C.M. Bryant ABSTRACT: Heat-denatured whey protein solutions are used to make ingredients that gel at low temperatures. This study examines the influence of holding temperature (65 to 90°C), holding time (5 to 30 min), protein concentration (2 to 12 wt%) and pH (3 to 8) on the rheology and appearance of heat-denatured whey protein solutions. The optimum preparation conditions required to produce non-gelled transparent solutions of heat-denatured proteins were established. The rate of cold-gelation after the addition of 200 mM NaCl to the heat-denatured whey protein solutions increased as their initial viscosity increased. It was possible to produce gels with different cold-gelling characteristics by altering the thermal preparation conditions. [source] Precooling of the femoral canal enhances shear strength at the cement,prosthesis interface and reduces the polymerization temperatureJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 9 2006Pang-Hsin Hsieh Abstract Preheating of the femoral stem in total hip arthroplasty improves the cement,prosthesis bond by decreasing the interfacial porosity. The main concern, however, is the potential thermal osteonecrosis because of an increased polymerization temperature. In this study, the effects of femoral canal precooling on the characteristics of the cement,stem interface were evaluated in an experimental model for three test conditions: precooling of the femoral canal, preheating of the stem (44°C), and a control in which stems were inserted at room temperature without thermal manipulation of the implant, cement, or bone. Compared to the control group, precooling of the femoral canal and preheating of the stem had similar effects on the cement,stem interface, with greater interfacial shear strength and a reduced porosity. Femoral canal precooling also produced a lower temperature at the cement,bone interface. No difference was found in the ultimate compressive strength of bone cement for the three preparation conditions. Based on this laboratory model, precooling of the femoral canal could improve shear strength and porosity at the stem,cement interface, minimize thermal injury, and maintain the mechanical strength of the cement. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [source] Preparation of HPLC chiral packing materials using cellulose tris(4-methylbenzoate) for the separation of chrysanthemate isomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2006Chiyo Yamamoto Abstract We investigated the separation of chrysanthemate isomers (1), particularly the (1R)-trans form, by high-performance liquid chromatography (HPLC) using polysaccharide derivatives, such as the phenylcarbamates and benzoates of cellulose and amylose, as the chiral stationary phases (CSPs). The chiral packing materials (CPMs) having a high chiral recognition for the chrysanthemic acid ethyl ester (1a) were prepared by coating cellulose tris(4-methylbenzoate) (2a) dissolved in solvents containing methyl benzoate or acetophenone as an additive on silica gel. The separation factor for 1a significantly depended on the preparation conditions of CPM 2a, such as the coating amount of 2a and the type and amount of additives. The chiral recognition ability created by imprinting the additives was lost when the CPM was heated at a high temperature, and was recovered by contacting it with the additive in a packed column. The structural change in 2a during these treatments was not clearly detected by spectroscopic methods. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5087,5097, 2006 [source] FUNCTIONALITY COMPARISON BETWEEN DERIVATIZED WHEY PROTEINS AND A PREGELATINIZED STARCHJOURNAL OF TEXTURE STUDIES, Issue 4 2002H. M. HUDSON ABSTRACT A process has been patented to produce stabilizing ingredients from whey proteins which are applicable over a wide range of typical food conditions and do not require heat or the addition of salts to induce thickening functionality. Once reconstituted in deionized water, solutions were evaluated and compared with water holding performance and rheological attributes of a pregelatinized cornstarch. Rotational viscometry was performed at pH values between 3 and 8, temperatures between 5 and 90C, and shear rates between 1 and 100 s,1. Derivatized whey protein powders and pregelatinized starch displayed pseudo-plastic behavior under shear at all temperatures tested. During temperature ramps from 5 to 90C, derivatized whey protein flow properties were essentially unchanged by varying pH. However, viscosity after the temperature increase was higher than initial values, possibly due to additional protein denaturation and hydrophobic interactions. Derivatized powders were stable and retained desired functionality over a wide range of food processing and preparation conditions and may therefore possess applicability to many products currently utilizing modified starches or hydrocolloids to texturize. [source] Raman Scattering Characterization of Polytype in Silicon Carbide Ceramics: Comparison with X-ray DiffractionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2003Shin-ichi Nakashima Raman scattering measurements have been made on SiC ceramics prepared from two powdered by sintering at different temperatures. The Raman spectra of starting powders have also been measured. The volume contents of the 4H and 15R polytype phases relative to that of the 6H phase in the ceramics are inferred from the Raman intensity of folded modes of the acoustic branches and compared with those determined from X-ray diffraction (XRD) analysis. A strong correlation is found between the results obtained from the two analyses. The 4H polytype contents estimated by Raman measurement for specimens prepared from one powder show a good agreement with those obtained by the XRD analysis. For the 15R polytype component there is a correlation between the contents inferred by the two techniques when the content is not very small. The results obtained by the two techniques demonstrate that the Raman spectroscopy as well as the XRD analysis is useful to study the natures and preparation conditions of SiC ceramics. [source] Microstructure Formation and Property of Chitosan-Poly(acrylic acid) Nanoparticles Prepared by Macromolecular ComplexMACROMOLECULAR BIOSCIENCE, Issue 10 2005Qi Chen Abstract Summary: We report here a study on the microstructure formation process of polymeric nanoparticles based on polyelectrolyte complexes. When polyanion poly(acrylic acid) (PAA) was dropped into polycation chitosan (CS) solution, CS-PAA nanoparticles with diverse microstructure would be formed under different experimental conditions. The microstructure of CS-PAA nanoparticles changed from solid spherical nanoparticles to core-shell separative ones and turned back to solid spherical ones with the variation of preparation conditions. The influence of molecular weight of CS and PAA, shell cross-linking, dropping temperature on the size, stability and morphology of CS-PAA nanoparticles were also studied. The nanoparticle size was affected by the molecular weight of CS and PAA, the ratio of amino group to carboxyl group (na/nc) and the incubation temperature as well. The shell-cross-linking provides a means to stabilize these nanoparticles. These nanoparticles can encapsulate plasmid DNA very well, which makes them have great potential in gene delivery. Microstructure of non-cross-linked CS-PAA nanoparticles, encapsulated plasmid DNA, at various na/nc. [source] Biodegradable Water Absorbent Synthesized from Bacterial Poly(amino acid)sMACROMOLECULAR BIOSCIENCE, Issue 3 2004Masao Kunioka Abstract Summary: Biodegradable hydrogels prepared by , -irradiation from microbial poly(amino acid)s have been studied. pH-Sensitive hydrogels were prepared by the , -irradiation of poly(, -glutamic acid) (PGA) produced by Bacillus subtilis and poly(, -lysine) (PL) produced by Streptomyces albulus in aqueous solutions. When the , -irradiation dose was 19 kGy or more, and the concentration of PGA in water was 2 wt.-% or more, transparent hydrogels could be produced. For the 19 kGy dose, the produced hydrogel was very weak, however, the specific water content (wt. of absorbed water/wt. of dry hydrogel) of this PGA hydrogel was approximately 3,500. The specific water content decreased to 200, increasing when the , -irradiation dose was over 100 kGy. Under acid conditions or upon the addition of electrolytes, the PGA hydrogels shrunk. The PGA hydrogel was pH-sensitive and the change in the volume of the hydrogel depended on the pH value outside the hydrogel in the swelling medium. This PGA hydrogel was hydrodegradable and biodegradable. A new novel purifier reagent (coagulant), made from the PGA hydrogels, for contaminated turbid water has been found and developed by Japanese companies. A very small amount of this coagulant (only 2 ppm in turbid water) with poly(aluminum chloride) can be used for the purification of turbid water. A PL aqueous solution also can change into a hydrogel by , -irradiation. The specific water content of the PL hyrdogel ranged from 20 to 160 depending on the preparation conditions. Under acid conditions, the PL hydrogel swelled because of the ionic repulsion of the protonated amino groups in the PL molecules. The rate of enzymatic degradation of the respective PL hydrogels by a neutral protease was much faster than the rate of simple hydrolytic degradation. [source] Polystyrene/Montmorillonite Nanocomposites Prepared by In Situ Intercalative Polymerization: Influence of the Surfactant TypeMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2004Hisham A. Essawy Abstract Summary: Na-montmorillonite (MMT) with a cation exchange capacity (CEC) of 90 meq/100 g was converted to MMT-CTAB and MMT-CPC by the intercalation of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC), respectively. The intercalation of CPC onto the basal space of the montmorillonite expanded the basal space from 12.19 to 21.47 Å, whereas in the case of CTAB, the spacing was only expanded to 19.35 Å. The MMT-CPC and MMT-CTAB forms were subsequently used as hosts for the preparation of polystyrene nanocomposites via intercalative free-radical polymerization of styrene. Different structures were obtained by varying the preparation conditions; the exfoliated and intercalated nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), and differential scanning calorimeter (DSC). The produced nanocomposites exhibited improved thermal stability in comparison with that of pure polystyrene above 400,°C especially in the case of the nanocomposites based on the MMT-CPC, in which intercalation exists. A glass transition temperature (Tg) could not be detected for the prepared nanocomposites using DSC; this was assumed to result from the restricted molecular motion of the polymer chains. XRD pattern of PS nanocomposites prepared by intercalative polymerization. [source] Preparation of smallest microparticles of poly- D,L -lactide by modified precipitation method: Influence of the process parametersMICROSCOPY RESEARCH AND TECHNIQUE, Issue 2 2008Ivana Jovanovi Abstract Biodegradable microspheres such as those made of poly- D,L -lactide (PDLLA) are widely investigated delivery systems for drugs or antigens. The aim of this study was to examine experimental conditions in order to produce PDLLA microspheres with the best properties for controlled and sustained drug delivery by the modified precipitation method. For this purpose, the following parameters were varied: co-solvent (methanol or ethanol), the concentration of stabilizer polyvinyl alcohol (PVA), chloroform-to-water ratio and the speed and time of homogenization. Scanning electron microscopy (SEM) and stereological analysis were used to characterize the particles. The average size and morphology of the microspheres varied substantially with preparation conditions from 8.44,1.25 ,m. Results showed that the smallest particles were obtained with methanol, 1% PVA and with 10 min of homogenization at 21,000 rpm. Microsc. Res. Tech., 2008. © 2007 Wiley-Liss, Inc. [source] Influence of top layer geometries on the electronic properties of pentacene and diindenoperylene thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2008M. Scharnberg Abstract Top layers have a pronounced influence on the electronic properties of molecular organic thin films. Here, we report about the changes induced by metallic and polymeric top layers and contacts. As test structures, model systems of diindenoperylene and pentacene crystalline molecular organic thin films are used. A very sensitive radiotracer technique is introduced to study the details of metal penetration during top contact formation. The influence of temperature, evaporation time, adhesion promoter and grain size of the organic film were examined. The electric currents passing through metal top contacts were found to vary by more than a factor of three, depending on the preparation conditions of the metal contact. Furthermore, the series resistance of chemically identical contacts that only differed in the morphology of the interface were found to show pronounced asymmetric conductivity behaviour. We also show that with the help of electret top layers, based on the Teflon-AF fluropolymer, the threshold voltage of an organic field effect transistor can be tuned by several volts. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The birefringence level of anisotropically nanostructured siliconPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2007J. Diener Abstract We present a detailed study of the anisotropic optical properties of mesoporous silicon layers prepared from substrates having different doping levels under various preparation conditions. It is demonstrated that the morphology of the layers strongly depends on the preparation conditions. The experimental data are explained in the framework of an effective medium model which takes into account different morphologies of the layers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Some properties of very thin Bi2Te3 layers prepared by laser ablationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2003R. Zeipl Abstract Thin layers of Bi2Te3 60,nm thickness were prepared by laser ablation in vacuum using KrF excimer laser. The energy of laser varied from 300 to 680,mJ and the laser energy density from 2 to 10,J,cm,2. The substrate temperature varied for different depositions in the interval of 20,500,°C. The influence of preparation conditions on Hall mobility, concentration of charge carriers and conductivity at room temperature is presented. Information about morphology and composition of prepared layers is given. [source] Study on superabsorbent composite.POLYMER COMPOSITES, Issue 8 2009In this work, the effects of different cation-exchanged montmorillonite on water absorbency of poly(acrylic acid- co -acrylamide)/montmorillonite/sodium humate (PAA-AM/MMT/SH) superabsorbent composite were systematically investigated under the same preparation conditions. The superabsorbents doped with different cation-exchanged montmorillonite were characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy technologies. Swelling behaviors of developing superabsorbent composite in various cationic saline solutions (NaCl, CaCl2, and FeCl3) were also investigated. The water absorbencies of superabsorbent composite with 20 wt% MMT and 30 wt% SH are 638, 723, 682, and 363 g g,1 in distilled water for incorporating natural Na+ -MMT, Li+ -exchanged MMT, Ca2+ -exchanged MMT, and Al3+ -exchanged MMT, respectively. The results showed that the cation-exchange process had some obvious influences on final water absorbency of superabsorbent composite. NaCl, CaCl2, and FeCl3 solutions did not alter the swelling characteristics of the superabsorbent materials at a concentration of less than 0.01 mM, however, a concentration of greater than 0.1 mM caused a collapse in the swelling curves. The excellent swelling-reswelling-swelling behavior and lower swelling rate testified that Al3+ -exchanged MMT can act as an assistant crosslinker in the polymeric network. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Formation and behaviour of low-temperature melting peak of quenched and annealed isotactic polypropylenePOLYMER INTERNATIONAL, Issue 2 2002ke Dudi Abstract The process of low-melting point (LMP) ,-phase formation in a quenched and annealed isotactic polypropylene (iPP) was studied by means of differential scanning calorimetry. The influence of preparation conditions (quenching and annealing temperatures, annealing times and sample thickness), together with the measurement parameters (heating and cooling rates), on the iPP melting behaviour are analysed. The results reveal a constant yield of LMP crystals over a wide range of quenching temperatures. This study also suggests that the LMP ,-crystals originate from the crystallization of polymer portions, which are somewhere between the amorphous and the smectic phase on the macromolecular scale of order. © 2001 Society of Chemical Industry [source] Formation and characterization of polymersomes made by a solvent injection methodPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2007M. E. Yildiz Abstract In this article a solvent injection method is described for vesicle formation using poly(butadiene)- b-poly(acrylic acid) diblock copolymers as the amphiphilic molecules. Vesicles composed of polymer bilayers are commonly referred to as polymersomes. Solvent injection is shown to be a rapid method for polymersome formation suitable to make large volumes of polymersome solution. The method can be manipulated to obtain a wide range of vesicle sizes depending on the polymer concentration and preparation conditions. Polymersome solutions in this study are characterized using dynamic light scattering (DLS), fluorescent microscopy, and electron microscopy. Polymersome sizes range from tens of nanometers to several microns. The membrane thickness of smaller polymersomes is found to lie between 14,20,nm. Larger polymersomes are found to have somewhat thicker membranes. The procedure involves the addition of polymers dissolved in an organic solvent to a stirred aqueous solution. The formation of polymersomes by this method is proposed to be governed by the limited mutual solubility of the two solvents and the simultaneous diffusion of solvent and water out of and in to initially formed organic solvent droplets. Copyright © 2007 John Wiley & Sons, Ltd. [source] Polycarbonate/SiC nanocomposites,influence of nanoparticle dispersion on molecular mobility and gas transport,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2-3 2005Martin Böhning Abstract Plasma synthesized silicon carbide (SiC) nanoparticles were dispersed in dichloromethane/poly(bisphenol-A-carbonate) (PC) solutions by high power ultrasonification. Samples were then prepared by film casting under well adapted preparation conditions. The influence of the SiC nanoparticles on the molecular mobility of the PC is studied by dielectric relaxation spectroscopy. No effect on the cooperative segmental mobility (glass transition) was detected. But the relaxation region corresponding to localized fluctuations is strongly broadened and the activation energy is reduced with increasing nanoparticle concentration. The most significant change was observed in the relaxation region between , - and , -process. The gas transport properties of these nanocomposite films are characterized in terms of permeability, diffusivity and solubility. Results can be interpreted based on an altered local free volume distribution and a change of molecular mobility of the polymer matrix near the nanoparticle surface which is in agreement with the dielectric results. Concentration dependent CO2 permeation experiments reveal a significant reduction of plasticization effects in the nanocomposites compared to the pure PC. Copyright © 2005 John Wiley & Sons, Ltd. [source] Role of the Preparation Procedure in the Formation of Spherical and Monodisperse Surfactant/Polyelectrolyte ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2007Yuxia Luan Dr. Abstract Complexes formed by a double-tail cationic surfactant, didodecyldimethyl ammonium bromide, and an anionic polyelectrolyte, an alternating copolymer of poly(styrene-alt-maleic acid) in its sodium salt form, were investigated with respect to variation in the charge ratio (x) between the polyelectrolyte negative charges and the surfactant positive charges. The morphology and microstructure of the complexes were studied by light microscopy and small-angle X-ray scattering for different preparation conditions. Independent of the sample preparation procedure and the charge ratio x, the X-ray results show that the microscopic structure of the complexes is a condensed lamellar phase. By contrast, the morphology of the complexes changes dramatically with the preparation procedure. The complexes formed by mixing a surfactant solution and a polyelectrolyte solution strongly depend on x and are always extremely heterogeneous in size and shape. Surprisingly, we show that, when the two solutions interdiffuse slowly, spherical complexes of micrometric and rather uniform size are systematically obtained, independently on the initial relative amount of surfactant and polyelectrolyte. The mechanism for the formation of these peculiar complexes is discussed. [source] | ||||||||||||||||||||||||||||||||||