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Microemulsion
Kinds of Microemulsion Terms modified by Microemulsion Selected AbstractsTransition from microemulsion to emulsion polymerization: Mechanism and final propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2004Kevin D. Hermanson Abstract Microemulsion and emulsion polymerization can have some similarities in starting conditions and polymerization mechanisms, but the resulting latices are unalike in particle size and molecular weight. Here we show that polymerizations can be formulated that display the characteristics often separately associated with microemulsion or emulsion polymerization. Kinetic modeling and particle size measurements show that emulsion polymerizations with initial concentrations close to the microemulsion,emulsion phase boundary demonstrate relatively fast consumption of monomer droplets and produce smaller particles. Because of their high surfactant concentrations, none of the emulsion polymerizations examined demonstrate the classical Smith,Ewart kinetics usually associated with emulsion polymerization. Instead these emulsion polymerizations have a long period of particle nucleation that subsides only after the disappearance of monomer droplets. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5253,5261, 2004 [source] Photoluminescent Properties of SrTiO3:Pr, Al Nanophosphors Synthesized by Microemulsion,Microwave HeatingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Qi Pang A novel approach for the preparation of SrTiO3:Pr, Al nanophosphors by microemulsion,microwave heating is reported in this paper. In comparison with the conventional solid-state sintering processes, this novel method provides a limited small space in a micelle for the formation of nanosized precursors and requires a very short heating time, thus reducing the energy consumption. As a result, small-sized particles with a narrow size distribution and high purity were produced. Transmission electron microscopy characterizations indicated that the synthesized particles were almost spherical with an averaging diameter of ,24 nm and agglomerates slightly. The X-ray diffraction analysis revealed the perovskite cubic structure of SrTiO3:Pr3+ nanoparticles. The luminescent of SrTiO3:Pr, Al phosphors were investigated by photoluminescence. Under 350 nm excitation, SrTiO3:Pr, Al showed a strong red emission, peaking at around 615 nm. The photoluminescence excitation intensity was enhanced by the addition of Al3+ ions. [source] One-Pot Fabrication of Supramolecular Polymer Particles via Situ Polymerization Stringed Assembly of a Two-Monomer MicroemulsionMACROMOLECULAR RAPID COMMUNICATIONS, Issue 4 2006Yongxin Wang Abstract Summary: A novel method, situ polymerization stringed assembly (SPSA), is proposed to prepare stable solid or hollow supramolecular polymer particles, which are assembled by numerous nanoparticles. By this method, the fabrication of primary nanoparticles (poly(methyl methacrylate), PMMA), the linkers (polyvinylpyrrolidone, PVP, chains) between the nanoparticles, and the final assembled solid or hollow particles could be achieved in just one-pot by methyl methacrylate (MMA)/N -vinylpyrrolidone (NVP) microemulsion polymerization under UV irradiation. The structures of the supramolecular particles can be changed from solid to hollow by tuning the mass ratio of MMA/NVP in the microemulsion. AFM, TEM, and SEM experiments are performed to identify the results. AFM image of the PMMA/PVP solid particles obtained from the photopolymerization of the microemulsion containing 20 wt.-% MMA, 10 wt.-% NVP, and 5,×,10,2 wt.-% BP. [source] ChemInform Abstract: Palladium-Catalyzed Suzuki Cross-Coupling Reactions in a Microemulsion.CHEMINFORM, Issue 23 2008Valery Vashchenko Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] In vitro permeation of diclofenac sodium from novel microemulsion formulations through rabbit skinDRUG DEVELOPMENT RESEARCH, Issue 1 2005Gülten Kantarc Abstract In order to increase topical penetration of the nonsteroidal anti-inflammatory drug, diclofenac sodium, new microemulsion formulations were prepared to increase drug solubility and in vitro penetration of the drug. The influence of dimethyl sulfoxide and propylene glycol were also investigated as enhancers on the in vitro penetration of diclofenac sodium using Franz diffusion cells using excised dorsal rabbit skin. Factorial randomized design was performed to analyze the results of in vitro permeation studies. Microemulsions prepared with isopropyl alcohol were superior to those prepared with propanol. Enhancers had different effects depending on the formulation. Propylene glycol was superior to dimethyl sulfoxide when incorporated into isopropyl alcohol microemulsion, whereas dimethyl sulfoxide was superior to propylene glycol in propanol microemulsions. There were no observable histopathological differences between the skin of the control group and the treated groups at the light microscope level due to swelling of the skin tissue. The present study shows that microemulsion formulations containing isopropyl alcohol as co-surfactant and propylene glycol as enhancer represent a promising approach for a topical vehicle for diclofenac sodium. Drug Dev. Res. 65:17,25, 2005. © 2005 Wiley-Liss, Inc. [source] Dual CD system-modified MEEKC method for the determination of clemastine and its impuritiesELECTROPHORESIS, Issue 19 2010Serena Orlandini Abstract A dual system of CDs was used for the first time in MEEKC with the aim of determining clemastine and its three main related impurities in both drug substances and tablets. The addition of methyl-,-cyclodextrin and heptakis(2,6-di- O -methyl)-,-cyclodextrin to the microemulsion pseudo-stationary phase was essential to increase the resolving power of the system to obtain a baseline separation among the compounds. The best microemulsion composition was identified by mixture design and the effects of the factors concentrations of CDs and voltage were investigated by a response surface study applying a Central Composite Design. In both cases, Derringer's desirability function made it possible to find the global optimum, which corresponded to the following combination: microemulsion, 89.8% 10,mM borate buffer pH 9.2, 1.5% n -heptane and 8.7% of SDS/n -butanol in 1:2 ratio; 18,mM methyl-,-cyclodextrin, 38,mM heptakis(2,6-di- O -methyl)-,-cyclodextrin, 17,kV. By applying these conditions, the separation was completed in about 5.5,min. The method was validated following International Conference on Harmonisation guidelines and was applied to a real sample of clemastine tablets. [source] Microstructure of microemulsion in MEEKCELECTROPHORESIS, Issue 4 2010Yuhua Cao Abstract The influences of the composition of microemulsion on the microstructure including dimensions and , potentials of microdroplets were measured in details. The average dynamic dimension of microdroplets was measured by dynamic laser light scattering, and , potential was determined to characterize average surface charge density of microdroplets. The experiment results showed that increase of the amount of surfactant resulted in decrease of microdroplet size but almost invariant , potential, which would enlarge migration time of the microdroplet in MEEKC. With increment of cosurfactant concentration, the microdroplet size had an increasing trend, whereas the , potential decreased. Thus, observed migration velocity of microdroplets increased, which made the separation window in MEEKC shortened. Neither dimension nor , potential of microdroplets changed by varying both the type and the amount of the oil phase. Adding organic solvent as modifier to microemulsion did not change the microdroplet size, but lowered , potential. The migration time of microdroplet still became larger, since EOF slowed down owing to organic solvent in capillary. So, besides increment of surfactant concentration, organic additive could also enlarge the separation window. Increase of cosurfactant concentration was beneficial for separation efficiency thanks to the looser structure of swollen microdroplet, and the peak sharpening might compensate for the resolution and peak capacity owing to a narrow separation window. Except the oil phase, tuning the composition of microemulsion would change the microstructure, eventually could be exploited to optimize the resolution and save analysis time in MEEKC. [source] Comparison of dodecoxycarbonylvaline microemulsion, solvent-modified micellar and micellar pseudostationary phases for the chiral analysis of pharmaceutical compoundsELECTROPHORESIS, Issue 24 2005Melissa No abstracts. [source] Microemulsion electrokinetic chromatography of drugs varying in charge and hydrophobicity: I. Impact of parameters on separation performance evaluated by multiple linear regression modelsELECTROPHORESIS, Issue 1 2004Valérie Harang Abstract The separation of anionic, cationic and neutral drugs in microemulsion electrokinetic chromatography (MEEKC) was studied with a statistical experimental design. The concentration of sodium dodecyl sulfate (SDS, surfactant), 1-butanol (co-surfactant) and borate buffer and the factors Brij 35 (surfactant), 2-propanol (organic solvent) and cassette temperature were varied simultaneously, while the parameters pH (9.2), the concentration of octane (oil, 0.8% w/w), the voltage (10 kV) and the dimension of the fused-silica capillary, were kept constant. Eight different model substances were chosen with different hydrophobicities. Two of the analytes were positively charged, two were negatively charged, and the remaining four were neutral or close to neutral at the pH explored. The importance of each parameter on the separation window, the plate height and the retention factor for each of the analytes was studied by means of multiple linear regression (MLR) models. A new response was evaluated for anions, the quotient between the effective mobility in the microemulsion and the effective mobility in the corresponding buffer. Factors affecting selectivity changes were also explored, and it was found that SDS and 2-propanol had the largest effect on selectivity. [source] Three Phase Microemulsion/Sol,Gel System for Aqueous C,C Coupling of Hydrophobic SubstratesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2008Dmitry Tsvelikhovsky Abstract Heck, Stille, Suzuki and three-component coupling reactions with hydrophobic substrates have been carried out in water. The substrates are initially transformed by a general procedure into a microemulsion, which consists of nearly 90,% water with the aid of sodium dodecyl sulfate and either PrOH or BuOH. The surfactant carries the molecules of the substrates to Pd(OAc)2 entrapped within a hydrophobicitized silica sol,gel matrix where the coupling between the substrates is assumed to take place. The products are then returned by the surfactant into the microemulsion from which it can be released. The immobilized palladium catalyst is leach proof and recyclable. It can be used in various coupling processes at least six times without loss of activity. Experiments with D2O have revealed that the water does not take part in the coupling process, but it has an effect on the pore size of the sol,gel matrix, which hosts the palladium catalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Study of association thermodynamics between crystal violet and sodium bis(2-ethylhexyl)sulfosuccinate and kinetics of basic fading of crystal violet in microemulsionsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2008Zhi Yun Chen The thermodynamics of the association between 4,4,,4,-tris(dimethyl-amino)triphenylmethyl chloride (crystal violet or CV) and sodium bis(2-ethylhexyl)-sulfosuccinate (aerosol OT or AOT) in water/AOT/n -decane microemulsion and the kinetics of the basic hydrolysis of CV in a water-in-oil microemulsion were investigated by UV,vis spectroscopic measurements. An association model of CV and AOT was used to analyze the experimental data to obtain the association constants at various temperatures. By taking the association into account, the "actual" rate constants and the activation energies of the basic hydrolysis of CV in the media of water/AOT/oil were obtained. The difference in thermodynamics and kinetics between the two media of water/AOT/n -decane and water/AOT/isooctane is discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 294,300, 2008 [source] Temperature and pressure effects on structural formations in a ternary microemulsionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000M. Nagao Small angle neutron scattering experiments were conducted on a temperature-induced phase transition in a ternary microemulsion composed of AOT (dioctyl sulfosuccinate sodium salt), D2 O and n -decane and the results were compared with those of pressure-induced one. Although the static features of both the temperature- and the pressure-induced phase behaviour were similar, a temperature dependence of its characteristic repeat distance at high temperature was quite different from a pressure dependence of that at high pressure. Neutron spin echo experiments were also performed on both the phase transitions. The dynamics of the high temperature phase was different from that of the high pressure phase. These results indicated that the effect of pressure on the structural formation was different from that of temperature. [source] Effect of polymerization method on structure and properties of cationic polyacrylamideJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Yinghua Shen Abstract Acrylamide and 2-(methacryloyloxy)ethyltrimethylammonium chloride (AM/MADQUAT) copolymers were synthesized by solution and inverse microemulsion polymerization using (NH4)2S2O8/NaHSO3 as redox initiator at the same feed mole ratio, and their microstructure, such as sequence distribution and composition distribution, was calculated from monomer reactivity ratios of different polymerization methods. The results show that charge distribution is more uniform for copolymer prepared in inverse microemulsion than that in solution, and copolymer composition distribution is close to unity, and maintains approximately at the feed ratio. Furthermore, the influence of the two structures of cationic polyacrylamides on kaolinite floc size and effective floc density, reduction of Zeta potential and floc compressive yield stress had been investigated at pH 7. The results show that the kaolinite floc size and effective floc density are strongly dependent upon copolymer microstructure, with greater floc size and lower effective floc density being observed for copolymer prepared in inverse microemulsion than for that in solution. Copolymer microstructure has a marked effect on the Zeta potential, whose reduction in the magnitude was much greater in the presence of copolymer prepared in inverse microemulsion than that in solution. Greater compressive yield stress was achieved for the strong flocs produced by copolymer prepared in inverse microemulsion than for the weak flocs produced by that in solution. The difference in flocs compressive yield stress may be attributed to flocs structure. Therefore, in this article, a correlation between the cationic polyacrylamide structure and flocculation property for kaolinite suspension was established. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Extraction and recovery of gold from KAu(CN)2 using cetyltrimethylammonium bromide microemulsionsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2001Tian-Xi Zhang Abstract Extraction and stripping of KAu(CN)2 from alkaline solution by a w/o microemulsion formed with cetyltrimethylammonium bromide (CTAB) using 198Au(I) tracer has been investigated. Various parameters, such as the Au(I) concentration in aqueous phase, concentrations of halide ions, NH4SCN and thiodiethylene glycol in stripping solution as well as the relationship between water and Au(I) concentration in the organic phase in the extraction and stripping of Au(I) were studied. The results show that almost all of the Au(I) in the aqueous phase was extracted into the organic phase. The water content decreased significantly with an increase in Au(I) concentration in the organic phase, contrary to the results of a system with tributyl phosphate (TBP) as cosolvent. Almost all of the extracted Au(I) (,98%) can be recovered with pure thiodiethylene glycol as the stripping agent, and ,93% of the Au(I) is stripped with high concentrations of NH4SCN(>3.0,mol,dm,3) or KI (>2.0,mol,dm,3). © 2001 Society of Chemical Industry [source] SHELF LIFE OF FRESH NOODLES AS AFFECTED BY THE FOOD GRADE MONOLAURIN MICROEMULSION SYSTEMJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2008XIAOWEI FU ABSTRACT Food grade monolaurin (the glycerol monoester of lauric acid) microemulsions (MMEs) based on multicomponent mixtures and the effects of MMEs on the shelf life of fresh noodles were studied. A microemulsion system consisting of monolaurin (M), surfactants (Tween 20 and Tween 80, Wenzhou Qingming Chemical Engineering Company, Wenzhou, Zhejiang, China ) and cosurfactant (pentanol and dodecanol) dispersed in distilled water was used. The influence of surfactants on the phase behavior was studied in this article. Subsequently, two MMEs with large oil in water regions have demonstrated the enhanced antimicrobial activities against Bacillus subtilis, Escherichia coli, Aspergillus niger and Penicillium digitatum, compared to monolaurin (M) alone. In addition, the shelf life of fresh noodles prepared with monolaurin (M) alone was about 4 days, whereas MMEs extended shelf life by 10 days at least when stored at 37C. PRACTICAL APPLICATIONS The effect of monolaurin microemulsion (MME) as antimicrobial agents in foods, especially those neutral foods such as noodles, is obvious, and MME has demonstrated a much longer shelf life of fresh noodles than M alone. In addition, for those neutral foods other than fresh noodles, the application of MMEs can also be studied. [source] Development of clinical dosage forms for a poorly water-soluble drug II: Formulation and characterization of a novel solid microemulsion preconcentrate system for oral delivery of a poorly water-soluble drugJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2009Ping Li Abstract The solution of a poorly water-soluble drug in a liquid lipid,surfactant mixture, which served as a microemulsion preconcentrate, was converted into a solid form by incorporating it in a solid polyethylene glycol (PEG) matrix. The solid microemulsion preconcentrates thus formed consisted of Capmul PG8 (propylene glycol monocaprylate) as oil, Cremophor EL (polyoxyl 35 castor oil) as surfactant, and hydrophilic polymer PEG 3350 as solid matrix. The drug (aqueous solubility: 0.17 µg/mL at pH 1,8 and 25°C) was dissolved in a melt of the mixture at 65,70°C and then the hot solution was filled into hard gelatin capsules; the liquid gradually solidified upon cooling below 55°C. The solid system was characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), confocal Raman microscopy (CRM), and the dispersion testing in water. It was confirmed that a solid microemulsion preconcentrate is a two-phase system, where clusters of crystalline PEG 3350 formed the solid structure (m.p. 55,60°C) and the liquid microemulsion preconcentrate dispersed in between PEG 3350 crystals as a separate phase. The drug remained dissolved in the liquid phase. In vitro release testing showed that the preconcentrate dispersed readily in water forming a microemulsion with the drug dissolved in the oil particles (<150 nm) and the presence of PEG 3350 did not interfere with the process of self-microemulsification. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:1750,1764, 2009 [source] IPM/DOSS/water microemulsions as reactors for silver sulfadiazine nanocrystal synthesisJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2005Jerry Nesamony Abstract The first goal of this work was the preparation of a water-in-oil microemulsion from components generally regarded as safe for use in humans. Stable formulations without need of a co-surfactant were prepared from isopropyl myristate (IPM), dioctyl sodium sulfosuccinate (DOSS), and water. A ternary phase diagram was prepared for the IPM/DOSS/water system. The IPM/DOSS/water microemulsions were characterized by conductivity and dynamic laser light scattering (DLS). The results obtained from conductivity experiments indicate conductivity values of less than 1 ,S/cm and were consistent with the formation of w/o microemulsions. The DLS results showed that the emulsified water droplets had an average diameter range of 9.2 to 19.7 nm, depending on composition. Modulation of the droplet size is possible by varying the water to DOSS molar ratio and DOSS to IPM ratio. The second goal of this work was the preparation of silver sulfadiazine (AgSD) nanoparticles. It was hypothesized that two separate microemulsions containing dispersed aqueous droplets of either sodium sulfadiazine or silver nitrate would react when mixed. The DLS results are consistent with the successful formation of submicron AgSD crystals. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1310,1320, 2005 [source] Tea tree oil concentration in follicular casts after topical delivery: Determination by high-performance thin layer chromatography using a perfused bovine udder modelJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2005S.S. Biju Abstract Tea tree oil, a popular antimicrobial agent is recommended for the treatment of acne vulgaris, a disease of the pilosebaceous unit. Tea tree oil formulations (colloidal bed, microemulsion, multiple emulsion, and liposomal dispersion containing 5% w/w tea tree oil) were applied to bovine udder skin. The follicular uptake of tea tree oil upon application was determined by a cyanoacrylate method. Tea tree oil was determined by quantifying terpinen-4-ol content using high-performance thin layer chromatography. The accumulation of tea tree oil in the follicular casts was 0.43,±,0.01, 0.41,±,0.009, 0.21,±,0.006, and 0.16,±,0.005 percentage by weight (milligram oil/gram of sebum plug) for microemulsion, liposomal dispersion, multiple emulsion, and colloidal bed, respectively. This is the first study of its kind to quantify tea tree oil concentration in the follicles. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:240,245, 2005 [source] Dermal delivery of desmopressin acetate using colloidal carrier systemsJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 4 2005Melkamu Getie Recently, the transdermal route has received attention as a promising means to enhance the delivery of drug molecules, particularly peptides, across the skin. In this work, the skin penetration profiles of desmopressin acetate from a colloidal system (water-in-oil microemulsion) and an amphiphilic cream, a standard formulation, were determined using Franz diffusion cells and compared. In the case of the microemulsion, the total percentages of dose obtained from different skin layers (stratum corneum to subcutaneous tissue) were 3.30 ± 0.67, 7.37 ± 2.43 and 15.54 ± 2.72 at 30, 100 and 300 min, respectively. Similarly, 5.19 ± 0.96, 8.04 ± 0.97 and 14.4 ± 5.15% of the dose applied was extracted from the skin treated with the cream. About 6% of the applied dose reached the acceptor compartment from the microemulsion instead of 2% from the cream within 300 min. The concentration of drug that penetrated into the upper layers of the skin was higher from the cream than from the microemulsion at all time intervals. On the other hand, a higher amount of drug was found in the deeper skin layers and in the acceptor compartment from the microemulsion. [source] In-vitro release and oral bioactivity of insulin in diabetic rats using nanocapsules dispersed in biocompatible microemulsionJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 4 2002Suchat Watnasirichaikul This study evaluated the potential of poly(iso -butyl cyanoacrylate) (PBCA) nanocapsules dispersed in a biocompatible microemulsion to facilitate the absorption of insulin following intragastric administration to diabetic rats. Insulin-loaded PBCA nanocapsules were prepared in-situ in a biocompatible water-in-oil microemulsion by interfacial polymerisation. The microemulsion consisted of a mixture of medium-chain mono-, di- and tri-glycerides as the oil component, polysorbate 80 and sorbitan mono-oleate as surfactants and an aqueous solution of insulin. Resulting nanocapsules were approximately 200 nm in diameter and demonstrated a high efficiency of insulin entrapment (> 80%). In-vitro release studies showed that PBCA nanocapsules could suppress insulin release in acidic media and that release at near neutral conditions could be manipulated by varying the amount of monomer used for polymerisation. Subcutaneous administration of insulin-loaded nanocapsules to diabetic rats demonstrated that the bioactivity of insulin was largely retained following this method of preparing peptide-loaded nanocapsules and that the pharmacodynamic response was dependent on the amount of monomer used for polymerisation. The intragastric administration of insulin-loaded nanocapsules dispersed in the biocompatible microemulsion resulted in a significantly greater reduction in blood glucose levels of diabetic rats than an aqueous insulin solution or insulin formulated in the same microemulsion. This study demonstrates that the formulation of peptides within PBCA nanocapsules that are administered dispersed in a microemulsion can facilitate the oral absorption of encapsulated peptide. Such a system can be prepared in-situ by the interfacial polymerisation of a water-in-oil biocompatible microemulsion. [source] Recent advances in controlled/living radical polymerization in emulsion and dispersionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2008Jung Kwon Oh Abstract Effective ways to conduct controlled/living radical polymerization (CRP) in emulsion systems are necessary for commercial latex production without significant modification of current industrial facilities. Conducting CRP in emulsion media is more complicated and more challenging than its application in homogeneous bulk. These challenges come from the intrinsic kinetics of emulsion polymerization. They include mass transport, slow chain growth mechanism, and exit of short radicals from polymeric particles. This review describes the recent developments of CRP in heterogeneous dispersion, including miniemulsion, microemulsion, dispersion, and especially emulsion. Various approaches for conducting emulsion CRP are detailed, including controlled seeded emulsion polymerization, nanoprecipitation, use of short oligomers as macroinitiators for in situ block copolymerization, and RAFT-mediated self-assembly. In addition many remaining challenges of the current methods barring wide spread industrial application of emulsion CRP are also suggested. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6983,7001, 2008 [source] Synthesis and characterization of carbon nanotube/polypyrrole core,shell nanocomposites via in situ inverse microemulsionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2005Yijun Yu Abstract We demonstrate here a feasible approach to the preparation of multiwalled carbon nanotube (MWNT)/polypyrrole (PPy) core,shell nanowires by in situ inverse microemulsion. Transmission electron microscopy and scanning electron microscopy showed that the carbon nanotubes were uniformly coated with a PPy layer with a thickness of several to several tens of nanometers, depending on the MWNT content. Fourier transform infrared spectra suggested that there was strong interaction between the ,-bonded surface of the carbon nanotubes and the conjugated structure of the PPy shell layer. The thermal stability and electrical conductivity of the MWNT/PPy composites were examined with thermogravimetric analysis and a conventional four-probe method. In comparison with pure PPy, the decomposition temperature of the MWNT/PPy (1 wt % MWNT) composites increased from 305 to 335 °C, and the electrical conductivity of the MWNT/PPy (1 wt % MWNT) composites increased by 1 order of magnitude. The current,voltage curves of the MWNT/PPy nanocomposites followed Ohm's law, reflecting the metallic character of the MWNT/PPy nanocomposites. The cyclic voltammetry measurements revealed that PPy/MWNT composites showed an enhancement in the specific charge capacity with respect to that of pure PPy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6105,6115, 2005 [source] Microemulsion copolymerization of styrene and acrylonitrile with n -butanol as the cosurfactantJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2005Yuanchang Shi Abstract The microemulsion copolymerization of styrene and acrylonitrile in an n -butanol/cetyltrimethylammonium bromide/oil/water microemulsion system was studied. The solubilization sites of the two monomers were determined with an NMR technique. The results showed that the solubilization behaviors of the two monomers were quite different. Most of the styrene was solubilized in the palisade layer of the microemulsion, whereas the acrylonitrile had an equilibrium distribution in the aqueous phase and palisade layer of the microemulsion. The reactivity ratios of styrene and acrylonitrile in the microemulsion system were different from those in other media. The effect of the monomer feed composition on the copolymerization kinetics was investigated, and the mechanism of nucleation of the latex particles was examined. The experimental results showed that the copolymerization loci were changed from the microemulsion droplets to the aqueous phase when the concentration of acrylonitrile in the monomer feed reached approximately 80%; this could be further proved by the effect of the monomer feed composition on the copolymerization kinetics. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 203,216, 2005 [source] Transition from microemulsion to emulsion polymerization: Mechanism and final propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2004Kevin D. Hermanson Abstract Microemulsion and emulsion polymerization can have some similarities in starting conditions and polymerization mechanisms, but the resulting latices are unalike in particle size and molecular weight. Here we show that polymerizations can be formulated that display the characteristics often separately associated with microemulsion or emulsion polymerization. Kinetic modeling and particle size measurements show that emulsion polymerizations with initial concentrations close to the microemulsion,emulsion phase boundary demonstrate relatively fast consumption of monomer droplets and produce smaller particles. Because of their high surfactant concentrations, none of the emulsion polymerizations examined demonstrate the classical Smith,Ewart kinetics usually associated with emulsion polymerization. Instead these emulsion polymerizations have a long period of particle nucleation that subsides only after the disappearance of monomer droplets. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5253,5261, 2004 [source] An initial assessment of the use of gradient elution in microemulsion and micellar liquid chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17-18 2004Simon M. Bryant Abstract Novel microemulsion and micellar HPLC separations have been achieved using gradient elution and columns packed with reverse phase material. Initial attempts at gradient microemulsion liquid chromatography proved impossible on use of a microemulsion successfully used in capillary electrophoresis. Optimisation of the microemulsion composition allowed the generation of stable microemulsions to achieve separations in HPLC. The novel use of organic-solvent micellar chromatography in gradient elution mode was shown to give efficient separations. A range of efficient separations of pharmaceuticals and related impurities were obtained. Acidic, basic, and neutral solutes were resolved covering a wide range of water solubilities and polarities. Elution times were in the order of 4,15 minutes. Separations were briefly compared to those accomplished with a micellar HPLC system. It is proposed that gradient elution in both microemulsion and micellar HPLC can be regarded as a highly successful means of achieving resolution of complex mixtures and should be considered for routine analysis and further investigation. [source] Photoluminescent Properties of SrTiO3:Pr, Al Nanophosphors Synthesized by Microemulsion,Microwave HeatingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Qi Pang A novel approach for the preparation of SrTiO3:Pr, Al nanophosphors by microemulsion,microwave heating is reported in this paper. In comparison with the conventional solid-state sintering processes, this novel method provides a limited small space in a micelle for the formation of nanosized precursors and requires a very short heating time, thus reducing the energy consumption. As a result, small-sized particles with a narrow size distribution and high purity were produced. Transmission electron microscopy characterizations indicated that the synthesized particles were almost spherical with an averaging diameter of ,24 nm and agglomerates slightly. The X-ray diffraction analysis revealed the perovskite cubic structure of SrTiO3:Pr3+ nanoparticles. The luminescent of SrTiO3:Pr, Al phosphors were investigated by photoluminescence. Under 350 nm excitation, SrTiO3:Pr, Al showed a strong red emission, peaking at around 615 nm. The photoluminescence excitation intensity was enhanced by the addition of Al3+ ions. [source] 12-month follow-up analysis of a multicenter, randomized, prospective trial in de novo liver transplant recipients (LIS2T) comparing cyclosporine microemulsion (C2 monitoring) and tacrolimus,,LIVER TRANSPLANTATION, Issue 10 2006Gary Levy The LIS2T study was an open-label, multicenter study in which recipients of a primary liver transplant were randomized to cyclosporine microemulsion (CsA-ME) (Neoral) (n = 250) (monitoring of blood concentration at 2 hours postdose) C2 or tacrolimus (n = 245) (monitoring of trough drug blood level [predose]) C0 to compare efficacy and safety at 3 and 6 months and to evaluate patient status at 12 months. All patients received steroids with or without azathioprine. At 12 months, 85% of CsA-ME patients and 86% of tacrolimus patients survived with a functioning graft (P not significant). Efficacy was similar in deceased- and living-donor recipients. Significantly fewer hepatitis C,positive patients died or lost their graft by 12 months with CsA-ME (5/88, 6%) than with tacrolimus (14/85, 16%) (P < 0.03). Recurrence of hepatitis C virus in liver grafts was similar in each group. Based on biopsies driven by clinical events, the mean time to histological diagnosis of hepatitis C virus recurrence was significantly longer with CsA-ME (100 ± 50 days) than with tacrolimus (70 ± 40 days) (P < 0.05). Median serum creatinine at 12 months was 106 ,mol/L with CsA-ME and with tacrolimus. More patients who were nondiabetic at baseline received antihyperglycemic therapy in the tacrolimus group at 12 months (13% vs. 5%, P < 0.01). Of patients who were diabetic at baseline, more tacrolimus-treated individuals required anti-diabetic treatment at 12 months (70% vs. 49%, P = 0.02). Treatment for de novo or preexisting hypertension or hyperlipidemia was similar in both groups. In conclusion, the efficacy of CsA-ME monitored by blood concentration at 2 hours postdose and tacrolimus in liver transplant patients is equivalent to 12 months, and renal function is similar. More patients required antidiabetic therapy with tacrolimus regardless of diabetic status at baseline. Liver Transpl 12:1464,1472, 2006. © 2006 AASLD. [source] Cyclosporine exposure and calcineurin phosphatase activity in living-donor liver transplant patients: Twice daily vs. once daily dosingLIVER TRANSPLANTATION, Issue 2 2006Masahide Fukudo We have compared the pharmacokinetics and pharmacodynamics of cyclosporine between once- and twice-daily dosing regimens in de novo patients of living-donor liver transplantation (LDLT). A total of 14 patients were enrolled in this study, who had received cyclosporine microemulsion (Neoral) twice a day (BID, n = 5) or once daily in the morning (QD, n = 9) after transplantation. On postoperative day (POD) 6, the QD regimen significantly increased cyclosporine exposure; the blood concentration at 2 hours postdose (C2) and area under the concentration-time curve (AUC) for 4 hours (AUC0,4), compared with the BID regimen. Moreover, the area under the calcineurin (CaN) activity in peripheral blood mononuclear cells time-curve (AUA) for 12 hours (AUA0,12) and 24 hours (AUA0,24) were decreased by approximately 42 and 25% with the QD regimen relative to the BID regimen, respectively. The C2 level was significantly correlated with the AUC0,4 (r2 = 0.95), which was negatively related to the AUA0,12 with a large interindividual variability (r2 = 0.59). However, a significant correlation was found between the AUA0,12 or AUA0,24 and CaN activity at trough time points. According to a maximum inhibitory effect attributable to the drug (Emax) model, the mean estimates of Emax and the Cb value that gives a half-maximal effect (EC50) for CaN inhibition were not significantly different between the 2 groups, respectively. These findings suggest that a once daily morning administration of cyclosporine may improve oral absorption and help to provide an effective CaN inhibition early after LDLT. Furthermore, CaN activity at trough time points would be a single surrogate predictor for the overall CaN activity throughout dosing intervals following cyclosporine administration. Liver Transpl 12:292,300, 2006. © 2006 AASLD. [source] Phase behaviour of microemulsions with lubricant base oil as the oil phaseLUBRICATION SCIENCE, Issue 7 2009Ya Lu Abstract Appropriate surfactants and co-surfactants were chosen to prepare a microemulsion system with lubricant base oil as the oil phase. The phase behaviour of the microemulsion at different temperatures and at different oil/water mass ratios was assessed on the basis of conductivity measurements. Microemulsions and a bi-continuous microstructure were obtained when the oil/water mass ratio was below 0.33. An analysis of the conductivity behaviour of the microemulsions revealed that different conductive mechanisms are operative at different water contents. Activation energies (,E) were determined. The results showed that ,E increases with increasing water content. The data and the derived relationship provided a basis for preparing metalworking microemulsions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Surface Area Effects in Hydroxyapatite/Poly(, -caprolactone) NanocompositesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2009Jasmeet Kaur Abstract In order to understand the contribution of nanoparticle surface area to the properties of nanocomposite materials, hydroxyapatite nanoparticles with different specific surface areas (60 m2,·,g,1 and 111 m2,·,g,1) were synthesized using reverse microemulsion and processed into nanocomposites. Experimental results indicated that the thermomechanical reinforcement did show a dependence on nanoparticle surface area, although the transition temperatures did not. The reinforcement trends were dependent on temperature, suggesting that the nanoparticles had a greater impact on the amorphous polymer chains. The reinforcement above Tg may be plotted against nanoparticle surface area to obtain a single reinforcement trend, suggesting that surface area is a general parameter for nanocomposite property control. 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