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Low Viscosity (low + viscosity)
Selected AbstractsCyclic Quaternary Ammonium Ionic Liquids with Perfluoroalkyltrifluoroborates: Synthesis, Characterization, and PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2006Zhi-Bin Zhou Dr. Abstract New cyclic quaternary ammonium salts, composed of N -alkyl(alkyl ether)- N -methylpyrrolidinium, -oxazolidinium, -piperidinium, or -morpholinium cations (alkyl=nC4H9, alkyl ether=CH3OCH2, CH3OCH2CH2) and a perfluoroalkyltrifluoroborate anion ([RFBF3],, RF=CF3, C2F5, nC3F7, nC4F9), were synthesized and characterized. Most of these salts are liquids at room temperature. The key properties of these salts,phase transitions, thermal stability, density, viscosity, conductivity, and electrochemical windows,were measured and compared to those of their corresponding [BF4], and [(CF3SO2)2N], salts. The structural effect on all the above properties was intensively studied in terms of the identity of the cation and anion, variation of the side chain in the cation (i.e., alkyl versus alkyl ether), and change in the length of the perfluoroalkyl group (RF) in the [RFBF3], ion. The reduction of Li+ ions and reoxidation of Li metal took place in pure N -butyl- N -methylpyrrolidinium pentafluoroethyltrifluoroborate as the supporting electrolyte. Such comprehensive studies enhance the knowledge necessary to design and optimize ionic liquids for many applications, including electrolytes. Some of these new salts show desirable properties, including low melting points, high thermal stabilities, low viscosities, high conductivities, and wide electrochemical windows, and may thus be potential candidates for use as electrolytes in high-energy storage devices. In addition, many salts are ionic plastic crystals. [source] Synthesis of Carbon-Nanotube Composites Using Supercritical Fluids and Their Potential ApplicationsADVANCED MATERIALS, Issue 7 2009Zhimin Liu Abstract Carbon-nanotube (CNT) composites have attracted a lot of attention because of their potential applications in many fields. Here, recent advances in the synthesis of CNT composites using supercritical fluids (SCFs) are highlighted. SCFs exhibit unique features for the synthesis of composites because of their unusual properties, such as low viscosity, high diffusivity, near-zero surface tension, and tunability. Preliminary studies show that SCFs show unusual advantages for the synthesis of CNT composites. The morphologies and structures of the resultant CNT composites can be tuned by changing the solvent properties. The SCF methods not only provide a green route for the synthesis of composites, but also result in nanostructures that have not yet been produced by conventional methods. Moreover, the potential applications of the resultant CNT composites are also discussed. [source] Properties of Porous Si3N4/BN Composites Fabricated by RBSN TechniqueINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2010Ji-Xuan Liu Reaction bonding of silicon nitride (RBSN) technique combined with slip-casting shaping process was used to fabricate porous Si3N4/BN ceramic composites. Si/BN slurry with chemical stability, good dispersibility, and viscosity was prepared using glycerol trioleate (GTO) covering on Si surface and poly(acrylic acid) (PAA) as dispersant. The hydrolysis of Si was strongly prevented by GTO coating. The dispersibility of covered Si and BN suspensions were improved by PAA dispersant. Twenty volume percent covered Si/BN slurries with low viscosity were successfully casted. The cast bodies were dried at room temperature, debindered at 750°C and nitrided below 1450°C. The nitrided samples mainly consist of ,-Si3N4, ,-Si3N4, and h-BN. The composites exhibit homogeneous microstructure consisting of faceted particles, ,-Si3N4 nanowires and a large amount of pores. The porosity is 52.64% and the pore size is in the range of 60,300 nm. The composites show compressive strength of 16.6±1.5 MPa. The dielectric constant of the composite is about 3.1 and the dielectric loss is below 0.5% under different frequencies. [source] Morphology and mechanical and viscoelastic properties of rubbery epoxy/organoclay montmorillonite nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Amar Boukerrou Abstract The morphology and mechanical and viscoelastic properties of rubbery epoxy/organoclay montmorillonite (MMT) nanocomposites were investigated with wide-angle X-ray scattering (WAXS), transmission electron microscopy (TEM), tensile testing, and dynamic mechanical thermal analysis. An ultrasonicator was used to apply external shearing forces to disperse the silicate clay layers in the epoxy matrix. The first step of the nanocomposite preparation consisted of swelling MMT in a curing agent, that is, an aliphatic diamine based on a polyoxypropylene backbone with a low viscosity for better diffusion into the intragalleries. Then, the epoxy prepolymer was added to the mixture. Better dispersion and intercalation of the nanoclay in the matrix were expected. The organic modification of MMT with octadecylammonium ions led to an increase in the initial d -spacing (the [d001] peak) from 14.4 to 28.5 Å, as determined by WAXS; this indicated the occurrence of an intercalation. The addition of 5 phr MMTC18 (MMT after the modification) to the epoxy matrix resulted in a finer dispersion, as evidenced by the disappearance of the diffraction peak in the WAXS pattern and TEM images. The mechanical and viscoelastic properties were improved for both MMT and MMTC18 nanocomposites, but they were more pronounced for the modified ones. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 103: 3547,3552, 2007 [source] The renal effects of alginates isolated from brown seaweed Sargassum vulgareJOURNAL OF APPLIED TOXICOLOGY, Issue 3 2008Alessandra de Paula Alves Sousa Abstract Alginates isolated from Sargassum vulgare, present a strong antitumor activity, associated with kidney reversible damage, as analysed by histopathology of treated animals. In the present study, the renal alteration mechanisms of S. vulgare alginates were investigated using the isolated perfused rat kidney and the isolated perfused rat mesenteric blood vessel methods. The results showed that the effects of Sargassum vulgare low viscosity (SVLV) alginate were more potent than those of Sargassum vulgare high viscosity (SVHV) alginate in the isolated rat kidney. The SVLV alginate caused considerable changes in renal physiology, as shown by an increase in parameters such as perfusion pressure, renal vascular resistance, glomerular filtration rate, urinary flow and sodium, potassium and chloride excretion and by reduction of chloride tubular transport. The effects of SVHV were weaker than those of SVLV. The effects of SVLV on kidney could be related to direct vascular action as demonstrated with SVLV alginate on mesenteric blood vessels. In conclusion, the Sargassum vulgare alginate altered the renal function parameters evaluated. S. vulgare low viscosity alginate renal effects were more potent than S. vulgare high viscosity alginate. It is suggested that physicochemical differences between SVHV and SVLV could explain the differences found in the results. Copyright © 2007 John Wiley & Sons, Ltd. [source] Synthesis and characterization of hyperbranched polymers with increased chemical versatility for imprint lithographic resistsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2008Anzar Khan Abstract Hyperbranched polymers were prepared from a variety of mono- and difunctional monomers and used in the development of novel UV-imprint lithography (UV-IL) resists. The unique physical and chemical properties of these hyperbranched materials significantly increase the range of molecular systems that could be imprinted. Traditional challenges, such as the use of monomers that have low boiling points or the use of insoluble/highly crystalline momomers, are overcome by the preparation of hyperbranched polymers that incorporate these repeat units. In addition, the low viscosity of the hyperbranched macromolecules and the large number of reactive chain ends overcome many difficulties that are traditionally associated with the use of polymeric materials as imprint resists. Hyperbranched polymers containing up to 12 mol % pendant vinyl groups, needed for secondary crosslinking during imprinting, were prepared with a wide range of repeat unit structures and successfully imprinted with features from tens of microns to , 100 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6238,6254, 2008 [source] Rapid Prototyping of Piezoelectric Ceramics via Selective Laser Sintering and GelcastingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2004Dong Guo This article presents a new lost mold rapid prototyping method which combines selective laser sintering (SLS) and gelcasting techniques for fabricating piezoelectric ceramics. SLS was used to fabricate sacrificial molds of the desired structure of the ceramic part. Then aqueous PZT (lead zirconate titanate) suspension was cast in the mold and solidified in situ through formation of a three-dimensional network gel. Because the polymer mold can be easily removed at the initial stage of sintering and the gelcast PZT body has a high green strength, the desired geometry of the PZT part can be completely retained after sintering of the ceramics. Complex-shaped PZT parts were successfully fabricated after using concentrated PZT suspension with low viscosity. Densities and electrical properties, such as the d33, the relative permittivity ,, the dielectric loss tg, and the electromechanical coupling factor Kp of the gelcast PZT parts were also compared with those of the die-pressed PZT samples. The results indicated that the gel-forming process did not deteriorate the electrical properties of the samples, if proper dispersant was selected in developing concentrated ceramic slurry. [source] Effect of Oligosaccharide Alcohol Addition to Alumina Slurry and Translucent Alumina Produced by Slip CastingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2003Yuji Hotta A slurry used to produce dense green compacts by slip casting should exhibit low viscosity, high solids content, and good dispersion. Slurries with good characteristics were produced in the present study by adding oligosaccharide alcohol to an Al2O3 slurry with an NH4+ salt of poly(methacrylic acid) (NH4+ -PMA). The role of NH4+ -PMA and oligosaccharide alcohol in the Al2O3 slurry was examined by DTA, ,-potential measurement, high-pressure liquid chromatography, and viscometry. The viscosity of the slurry with NH4+ -PMA and oligosaccharide alcohol was lower than that of the slurry with NH4+ -PMA at a high solids content. Oligosaccharide alcohol did not interact with the Al2O3 surface. However, the Al2O3 slurry with NH4+ -PMA was influenced by the addition of oligosaccharide alcohol. We found that the dispersibility of the slurry was greatly improved by adding oligosaccharide alcohol. The transmittance of the Al2O3 ceramics produced by slip casting using the slurry with both NH4+ -PMA and oligosaccharide alcohol was higher than that of ceramics produced by slip casting using the slurry with NH4+ -PMA alone. The increased optical property resulted from low viscosity, which was attributed to the addition of oligosaccharide alcohol, at a high solids content. [source] The Influence of Solvent Properties and Functionality on the Electrospinnability of Polystyrene NanofibersMACROMOLECULAR MATERIALS & ENGINEERING, Issue 7 2006Cattaleeya Pattamaprom Abstract Summary: In order to produce nanometer-sized fibers at an industrial scale, not only the morphology but also the production rate of fibers is important. The effect of solvent properties and functionality on the production rate of electrospun PS nanofibers was investigated using eighteen different solvents. The solution concentration was varied between 10 and 30% w/v. Electrospinning of PS solutions was carried out at various applied voltages and tip-to-collector distances The production rate of the obtained PS nanofibers was quantified in terms of electrospinnability. We found that the chance for the resulting PS solution to be spinnable is greater for solvents with high dipole moment and low viscosity. The solvent that provided the highest electrospinnability for polystyrene was DMF and the functionalities that promoted high dipole moment and thus high spinnability were the carbonyl group and the nitrogen group with free electrons. General guidelines for choosing suitable solvents for successful production of electrospun nanofibers have also been proposed. SEM image of PS 685D at 200× magnification and the %-coverage of the fibers obtained by using DMF, chloroform, and 1,4-dioxane. [source] A Novel Process for Ultrasound-Induced Radical Polymerization in CO2 -Expanded FluidsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2005Maartje F. Kemmere Abstract Summary: A strong viscosity increase upon polymerization hinders cavitation and subsequent radical formation during an ultrasound-induced bulk polymerization. In this work, ultrasound-induced radical polymerizations of methyl methacrylate (MMA) have been performed in CO2 -expanded MMA in order to reduce the viscosity of the reaction mixture. For this purpose, the phase behavior of CO2/MMA systems has been determined. With temperature oscillation calorimetry, the influence of CO2 on the viscosity and on the reaction kinetics of ultrasound-induced polymerizations of MMA has been studied. In contrast to polymerizations in bulk, this technique shows that a low viscosity is maintained during polymerization reactions in CO2 -expanded MMA. As a consequence, a constant or even increasing polymerization rate is observed when pressurized CO2 is applied. Moreover, the ultrasound-induced polymer scission in CO2 -expanded MMA is demonstrated, which appears to be a highly controlled process. Finally, a preliminary sustainable process design is presented for the production of 10 kg/h pure PMMA (specialty product) in CO2 -expanded MMA by ultrasound-induced initiation. Process flow diagram of the ultrasound-induced polymerization of MMA in CO2 -expanded MMA. [source] Synthesis of High Solid-Content Latex using Alkali-Soluble Resin as Sole SurfactantMACROMOLECULAR RAPID COMMUNICATIONS, Issue 22 2004Marcelo do Amaral Abstract Summary: A novel polymerization procedure to synthesize latex stabilized by alkali-soluble resin (ASR) is detailed. According to this process, latexes with a high solid content and low viscosity are obtained using a substantially lower amount of ASR when compared with existing techniques. Similar rewet properties were found for the latexes obtained by a standard process and for the one obtained by the process described in this work. Comparison of the particle size distributions obtained by conventional emulsion polymerization (,) and by miniemulsion polymerization (,). [source] Damage evolution in low velocity impacted unreinforced vinyl ester 411-350 and 411-C50 resin systemsPOLYMER COMPOSITES, Issue 6 2000M. Motuku Assistant Professor Damage evolution in plaques made of vinyl ester resin systems was investigated as a function of specimen thickness, impact energy level and matrix material. Dow DERAKANE vinyl ester 411-350 and 411-C50 resin systems, which have low viscosity and are ideally suited for low-cost liquid processing techniques like vacuum assisted resin transfer molding (VARTM), were considered for the low velocity instrumented impact testing. Characterization of damage evolution was undertaken using optical microscopy and analysis of impact load histories recorded during the impact event. Radial cracking, perforations at the point of impact (in the form of a truncated cone), and damage resulting from the support constraints were identified as the dominant failure characteristics in both resin systems. Radial cracking, which originated from the bottom surface, was operative in all failed specimens and was attributed to the catastrophic failure due to extensive flexural tensile strength losses. For specimens that could deflect significantly, radial cracking and support-constraint-induced damage were the operative failure mechanisms. Radial cracking and through-thickness shearing led to failure in stiffer plaques. The DERAKANE 411-350-vinyl ester resin system was found more damage resistant than the 411-C50 system. [source] Interfacial instabilities in coextrusion flows of low-density polyethylenes: Experimental studiesPOLYMER ENGINEERING & SCIENCE, Issue 5 2000Costas Tzoganakis A fundamental investigation into the interfacial instability phenomenon was performed. Coextrusion experiments were carried out using well-characterized low-density (LDPE) resins in an effort to gain a better understanding of interfacial instability phenomena. The resins used were chosen carefully and included materials of high and low viscosity as well as broad and narrow molecular weight distributions (MWD). The experiments involved the coextrusion of either the same material in both layers or various combinations of the four materials and the focus of the work was to elucidate the effects of flow rates, molecular weight (MW) and MWD on interfacial instability. The effect of the geometry at the point where the materials merged was also investigated. It was concluded that there are essentially two types of interfacial instabilities and that the MW had the strongest effect on the occurrence of the "zig-zag" instability due to high interfacial stress while the breadth of the MWD had a strong effect on the appearance of the "wave" instability. Broad MWD materials had a greater tendency to exhibit interfacial instability, which is more due to layer ratio than processing conditions or die geometries. The results suggest that the origin of the "wave" type of interfacial instability is due to an extreme extensional deformation of the minor layer at the merge point and that the viscoelastic properties of adjacent layers determine the instability development. [source] Polymerizability, copolymerizability, and properties of cyanoacrylate-telechelic polyisobutylenes I: three-arm star cyanoacrylate-telechelic polyisobutylenePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10 2007Yongmoon Kwon Abstract This series of papers concern new materials for possible biological applications created by combining the chemistry of highly reactive cyanoacrylates (CAs) with polyisobutylene (PIB) rubbers. First, a new strategy for the synthesis of CA,telechelic PIBs is described. Subsequently, the strategy is employed for the synthesis of low viscosity (syringible) CA,telechelic three-arm star PIB [Ø(PIB,CA)3]. The intermediates of the synthesis route are characterized by 1H NMR spectroscopy. Injecting liquid Ø(PIB,CA)3 into living tissue (fresh chicken egg) produces a bolus of crosslinked PIB rubber. The spectacular oxidative resistance of this rubber is documented by its resistance to concentrated HNO3. A structural model of the crosslinked rubber obtained upon contacting Ø(PIB,CA)3 with proteinaceous tissue is proposed. Copyright © 2007 John Wiley & Sons, Ltd. [source] Hyperbranched polyesters and their application in dental composites: monomers for low shrinking compositesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2001J. E. Klee Abstract Using trimethylolpropane (TMP) and 2,2-bishydroxymethylpropionic acid (Bis-MPA), aliphatic hyperbranched polyesters (HBP) were synthesized, with a degree of branching of DB,=,0.47 and a degree of polymerization of Pn,=,16.5. Aromatic HBPs with repetitive units of 2,2-bis(4-hydroxyphenyl)pivalonic acid (Bis-PVA) lead to a higher DB,=,0.48 and Pn,=,30.5 compared to the aliphatic HBP. Reactive functionalization of the hyperbranched polymers was achieved via esterification of mixtures of methacrylic acid and carboxylic acids. In this manner, i -butyric acid and methacryloyl terminated HBPs were obtained. They have a low viscosity ranging from 200 to 364,Pa*s and exhibit relatively low volume shrinkage (1.9 to 3.6%) during photoinitiated cure. Dental composites with volume shrinkage of 0.5 to 1.5% have been prepared using these methacryloyl terminated HBPs in combination with a Ba/alumosilicate glass filler. Copyright © 2001 John Wiley & Sons, Ltd. [source] A Thermoreversible Polymer Mediates Controlled Release of Glial Cell Line-Derived Neurotrophic Factor to Enhance Kidney RegenerationARTIFICIAL ORGANS, Issue 8 2010Yousof Gheisari Abstract Previously, we reported that human mesenchymal stem cells (hMSCs) that were cultivated in growing embryos differentiated in an appropriate developmental milieu, thereby facilitating the development of a functional renal unit. However, this approach required transfection with an adenovirus that expressed glial cell line-derived neurotrophic factor (GDNF) to enhance the development of hMSC-derived renal tissue, and safety issues restrict the clinical use of such viral vectors. To circumvent this problem, we tested an artificial polymer as a means to diffuse GDNF. This GDNF-polymer, which exists in liquid form at 4°C but becomes a hydrogel upon heating to 37°C, was used as a thermoreversible switch, allowing the injection of hMSCs at low viscosity using a mouth pipette, with subsequent slow diffusion of GDNF as it solidified. The polymer, which was dissolved in a solution of GDNF at 4°C and then maintained at 37°C, acted as a diffuser of GDNF for more than 48 h. LacZ -transfected hMSCs and the GDNF-polymer (at 4°C) were placed in the nephrogenic sites of growing rat embryos that were maintained at 37°C. Forty-eight hours later, the resultant kidney anlagen were dissected out and allowed to continue developing for 6 days in vitro. Whole-organ X-Gal staining and fluorescence activated cell sorter analysis showed that the number of hMSC-derived cells was significantly increased in developed anlagen that have been generated from hMSCs plus GDNF-polymer compared with those from hMSCs plus GDNF-containing medium and was comparable to those from adenovirus-transfected hMSCs. These findings suggest that the GDNF-polymer can be used as a diffuser of GDNF for kidney organogenesis. [source] Enhancement of Monascus Pigment Production by the Culture of Monascus sp.BIOTECHNOLOGY PROGRESS, Issue 1 2006J101 at Low Temperature In general, high broth viscosity is a key factor to be considered in a submerged fermentation of filamentous fungi. High broth viscosity was also observed in a batch fermentation of Monascus sp. J101 at 30 °C. In a batch culture at 30 °C, most cell growth was accomplished within 48 h, which induced highly entangled clumps. The resultant high viscosity induced heterogeneity inside the fermentor, poor oxygen transfer, and low pigment yield. However, these problems could be overcome by reducing fungal growth rate through culture at low temperature (25 °C). Cell growth was moderate and continued for 120 h, and low viscosity was maintained. The DO levels remained at 50% or higher with good mixing. As a result, the pigment yield at 25 °C was 10 times greater than at 30 °C. [source] | |||||||||||||||||||||||||