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Acid Medium (acid + medium)
Kinds of Acid Medium Selected AbstractsTransformations of Spirocyclodimers of 1,3-Bis(ferrocenylmethylidene)-2-methylidenecycloalkanes in Acid Medium.CHEMINFORM, Issue 41 2002E. I. Klimova Abstract For Abstract see ChemInform Abstract in Full Text. [source] Effect of phosphonate additive on crystallization of gypsum in phosphoric and sulfuric acid mediumCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2002H. El-Shall Abstract Understanding the mechanisms of growth and inhibition during crystallization of calcium sulfate is of primary importance for many industrial applications. For instance, inhibition of the crystallization process may be required to prevent scale formation in pipes, boilers, heat exchangers, reactors, reverse osmosis membrane surfaces, cooling water systems, secondary oil recovery utilizing water flooding techniques and desalination evaporators, etc. On the other hand, control growth and morphology of gypsum crystals is desired in achieving higher filtration rate and higher productivity of phosphoric acid from phosphate rocks. In this regard, this basic study is carried out to understand effect of Aminotris (methylenephosphonic acid (ATMP) on calcium sulfate dihydrate (gypsum) crystallization. The time elapsed between the achievement of supersaturation and the appearance of a solid phase (termed as induction time) is measured under different supersaturation ratios ranging from 1.018 to 1.979. The data are used to calculate the surface energy, critical nucleus size, and crystal growth rates of gypsum under different conditions. The results show that, the induction time decreases exponentially with increasing the supersaturation ratio. In addition, the surface energy decreases with ATMP compared to the baseline (without ATMP). Interestingly, with addition of the ATMP, the crystals mean and median diameters are found to decrease. The inhibition efficiency ranges from 16% to 59% depending on supersaturation ratio. [source] Development and validation of fixed-time method for the determination of isoxsuprine hydrochloride in commercial dosages formsDRUG TESTING AND ANALYSIS, Issue 9 2010Dr Nafisur Rahman Abstract The main aim of this work was to develop a kinetic spectrophotometric method for the quantitative analysis of isoxsuprine hydrochloride in commercial tablets. The method is based on the reaction of isoxsuprine hydrochloride (ISx) with hydroxylamine hydrochloride and ammonium cerium (IV) nitrate in sulphuric acid medium at room temperature which resulted in the formation of yellow-coloured product peaking at 380 nm. The reaction is followed spectrophotometrically by measuring the absorbance as a function of time. Fixed time method (,A = A4,A2, where A2 and A4 refer to absorbance measurements taken at 2 and 4 min, respectively) was adopted for constructing the calibration curve which was found to be linear over the concentration range of 30,80 µgmL,1 with molar absorptivity of 5.95 × 103 L mol,1 cm,1. The method has been applied successfully to the determination of isoxsuprine hydrochloride in tablets. Statistical comparison (point and interval hypothesis tests) of the results showed that there is no significant difference between the proposed method and reference method. Copyright © 2010 John Wiley & Sons, Ltd. [source] Novel Thorium Membrane Sensors with Anionic Response Based on Trioctylphosphine Oxide and Toluate IonophoresELECTROANALYSIS, Issue 19 2008Abstract Two novel potentiometric polymeric membrane sensors for rapid and accurate determination of thorium are described. These are based on the use of trioctylphosphine oxide (TOPO) and thorium toluate (Th-TA) as ionophores dispersed in poly(vinyl chloride) matrix membranes plasticized with nitrophenyloctyl ether. In strong nitric acid medium, Th(IV) nitrate is converted into [Th(NO3)6]2, complex and sensed as anionic divalent ion which exclude most cationic effect. Validation of the assay methods using the quality assurance standards (linearity range, accuracy, precision, within-day variability, between-day-repeatability, lower detection limit and sensitivity) reveals excellent performance characteristics of both sensors. The sensors exhibit near-Nernstian response for 1.0×10,6,1.0×10,1 M Th over the pH range 2.5,4.5. Calibration slopes of ,32.3±0.3 and ,27.2±0.2,mV/decade, precision of ±0.5 and ±0.8% and accuracy of 98.8±0.9 and 97.9±0.7% are obtained with TOPO and Th-TA based sensors, respectively. Negligible interferences are caused by most interfering mono-, di-, tri-, tetra-, penta-, and hexa-valent elements commonly associated with thorium in naturally occurring minerals and ores. High concentrations of Cl,, F,, SO42,, and NO3, ions have no diverse effect. Complete removal of the effect of the interferents in complex matrices is achieved by retention of [Th(NO3)6]2, complex from 5,M nitric acid/methanol mixture (1,:,9,v/v) on a strong anion exchanger, washing out the cationic interferents followed by stripping off thorium anion complex and measurements. Both sensors are used for determining thorium in certified thorium ore samples (20,120,mg Th/kg) and some naturally occurring ores (200,600,mg Th/kg). The results obtained agree fairly well with the certified labeled values or the data obtained using X-ray fluorescence spectrometry [source] Kinetics and mechanism of the dehydration reaction of sarcosine to a bislactame through diacyclperoxide intermediate in strong acidic mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2009Homayoon Bahrami The influence of substitution on the amine functional group of glycine in the permanganic oxidation of such an ,-amino acid in moderately concentrated sulfuric acid medium has been investigated. Reaction products analysis has revealed that contrary to the usual ,-amino acid oxidation product, which is an aldehyde species, a valuable compound, namely 1,4-dimethylpiperazine-2,5-dione, has been obtained as the main product via a cheap, simple, efficient, and novel method. Sarcosine has been chosen as a substituted derivative of glycine, and the kinetics and mechanism of its permanganic oxidation have been investigated using a spectrophotometric technique. Conclusive evidence has proven delayed autocatalytic activity for Mn(II) in this reaction, analogous to some ,-amino acids. It has been revealed that such activity can show up when a certain concentration ratio of Mn(II) to sarcosine is built up in the medium, which we call the "critical ratio." The magnitude of the latter ratio depends on the sulfuric acid concentration. Considering the "delayed autocatalytic behavior" of Mn(II) ions, rate equations satisfying observations for both catalytic and noncatalytic routes have been presented. The reaction shows first-order dependence on permanganate ions and sarcosine concentrations in both catalytic and noncatalytic pathways, and apparent first-order dependence on Mn2+ ions in catalytic pathways. The correspondence of pseudo-order rate constants of the catalytic and noncatalytic pathways to Arrhenius and Eyring laws has verified "critical ratio" as well as "delayed autocatalytic behavior" concepts. The activation parameters associated with both pathways have been computed and discussed. Mechanisms for both catalytic and noncatalytic routes involving radical intermediates as well as a product having a diketopiperazine skeleton have been reported for the first time. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 689,703, 2009 [source] Mechanism of oxidation of alanine by chloroaurate(III) complexes in acid medium: Kinetics of the rate processesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2009Pratik K. Sen The kinetics of the oxidation of alanine by chloroaurate(III) complexes in acetate buffer medium has been investigated. The major oxidation product of alanine has been identified as acetaldehyde by 1H NMR spectroscopy. Under the experimental conditions, AuCl and AuCl3(OH), are the effective oxidizing species of gold(III). The reaction is first order with respect to Au(III) as well as alanine. The effects of H+ and Cl, on the second-order rate constant k2, have been analyzed, and accordingly the rate law has been deduced: k2, = (k1[H+][Cl,] + k3K4K5)/(K4K5 + [H+][Cl,]). Increasing dielectric constant of the medium has an accelerating effect on the reaction rate. Activation parameters associated with the overall reaction have been calculated. A mechanism involving the two effective oxidizing species of gold(III) and zwitterionic species of alanine, consistent with the rate law, has been proposed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 473,482, 2009 [source] Effect of surfactant micelles on the kinetics of oxidation of D -fructose by cerium(IV) in sulfuric acid mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2006Kabir-ud-Din Kinetics of the oxidation of D -fructose by cerium(IV) has been investigated both in the absence and presence of surfactants (cetyltrimethylammonium bromide, CTAB, and sodium dodecyl sulfate, SDS) in sulfuric acid medium. The reaction exhibits first-order kinetics each in [cerium(IV)] and [D -fructose] and inverse first order in [H2SO4]. The Arrhenius equation is found to be valid for the reaction between 30,50°C. A detailed mechanism with the associated reaction kinetics is presented and discussed. While SDS has no effect, CTAB increases the reaction rate with the same kinetic behavior in its presence. The catalytic role of CTAB micelles is discussed in terms of the pseudophase model proposed by Menger and Portnoy. The association constant Ks that equals to 286 mol,1 dm3 is found for the association of cerium(IV) with the positive head group of CTAB micelles. The effect of inorganic electrolytes (Na2SO4, NaNO3, NaCl) has also been studied and discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 18,25, 2006 [source] Kinetic study of the nitrosation of 1,3-dialkylureas in aqueous-perchloric acid mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2004Guillermo González-Alatorre The kinetics of the nitrosation of 1,3-dimethyl (DMU), 1,3-diethyl (DEU), 1,3-dipropylurea (DPU), 1,3-dibuthyl (DBU), and 1,3-diallylurea (DAU) were studied in a conventional UV/vis spectrophotometer in aqueous-perchloric acid media. The kinetic study was carried out using the initial rate method. The reaction rate observed was where Ka is the acidity constant of nitrous acid. The diureas exhibited the reactivity order DMU , DEU > DPU > DAU, which can be interpreted as a function of the steric impediment generated by the R alkyl group in the rate controlling step. A probable relationship between both the chemical reactivity and structure of the nitrosable substrate with the biological activity of the N-nitroso compounds generated is proposed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 273,279, 2004 [source] Kinetics and mechanism of oxidation of antimony(III) by keggin-type 12-tungstocobaltate(III) in aqueous hydrochloric acid mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2003B. D. Bhosale The reaction between Sb(III) and [CoIIIW12O40]5, proceeds with two, one-electron steps; formation of unstable Sb(IV) is the slow first step followed by its reaction with another oxidant in a fast step. The reaction rate is unaffected by the [H+] as there are no protonation equlibria involved with both the reactants, whereas the accelerating effect of chloride ion is due to the formation of an active chlorocomplex of the reductant, SbCl63,. Increase in the ionic strength and decrease in the relative permittivity of the medium increases the rate of the reaction, which is attributed to the formation of an outer-sphere complex between the reactants. The activation parameters were also determined and these values support the proposed mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 9,14, 2003 [source] Oxidative behavior and relative reactivities of some unsaturated compounds towards hexachloroiridate(IV) in perchloric acid mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2002Kalyan K. Sen Gupta The kinetics of the oxidation of styrene, cinnamic acid, and some of their substituted derivatives by hexachloroiridate(IV) in dimethyl formamide,water mixtures and in the presence of perchloric acid have been investigated. The reactions appear to proceed via the formation of an unstable intermediate 1:1 complex between iridium(IV) and the substrate, followed by the decomposition of the complex in the rate-determining step. Correlation with , yielded , values of ,4.0 and ,3.5 which suggests the formation of a cationic intermediate in the rate-determining step of the reaction. Subsequent cleavage of the carbon,carbon bond yielded the product aldehydes. Thermodynamic and activation parameters associated with the equilibrium and the rate-determining steps were also evaluated. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 411,417, 2002 [source] Synthesis and characterization of polyaniline films using Fenton reagentJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008M. M. Ayad Abstract The chemical oxidation of aniline to form polyaniline (PANI) films and powder samples was made using Fenton reagent as an oxidizing agent in aqueous sulfuric acid medium. The PANI films were monitored by using the quartz crystal microbalance and the electronic absorption techniques. The optimum concentration was determined and the results were justified by measuring the UV,vis absorption spectra for the in situ PANI films. The conductivity for the PANI films and powder samples, prepared in different conditions, was measured. Also, the IR spectra, X-ray and the thermogravimetric analysis for the PANI powder formed in the bulk were measured and compared with the polymer prepared using ammonium peroxydisulfate. A preliminary investigation to the dielectric properties of the polymer powder was measured and discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Amine functional chloroaniline acetaldehyde condensate-modified epoxy networksJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008T. Maity Abstract An investigation was carried out to modify the fracture toughness of cured diglycidyl ether of bisphenol-A (DGEBA) resin networks with amine functional chloroaniline acetaldehyde condensate (AFCAC) as toughening agent. The resulting networks displayed significantly improved fracture toughness. The AFCAC was synthesized by the condensation reaction of chloroaniline and acetaldehyde in the acid medium (pH-4) and characterized by FTIR and NMR spectroscopy, elemental analysis, viscosity measurements, and mole of primary and secondary amine analysis. The DGEBA and AFCAC were molecularly miscible but developed a two-phase microstructure upon network formation. Epoxy/AFCAC compositions were systematically varied to study the effect of concentration on the impact, adhesive, tensile, and flexural properties of modified networks. The dynamic mechanical analysis and scanning electron microscopy studies showed two-phase morphology in the cured networks where AFCAC particles were dispersed. The AFCAC-modified epoxy network was thermally stable up to around 338°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Comparison of the corrosion protection of mild steel by polypyrrole,phosphate and polypyrrole,tungstenate coatingsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008M. G. Hosseini Abstract The electrodeposition of polypyrrole,phosphate (PPy,P) and polypyrrole,tungstenate (PPy,W) on mild steel (MS) were achieved in an oxalic acid medium with cyclic voltammetry techniques. Adherent and homogeneous PPy,P and PPy,W films were obtained. The corrosion behavior of mild steel with phosphate (PPy,P) and tungstenate (PPy,W) composite coatings in 3.5% NaCl solutions were investigated through a potentiodynamic polarization technique, open-circuit potential,time curves, and electrochemical impedance spectroscopy (EIS). On the basis of a physical model for corrosion of mild steel composites, Zview (II) software was applied to the EIS to estimate the parameters of the proposed equivalent circuit. It was found that the PPy,W coatings could provide much better protection than the PPy,P and polypyrrole coatings. The effects of the phosphate and tungstenate process parameters on the morphology and structure of the passive films were investigated by scanning electron microscopy and electron dispersion X-ray analyses. The results reveal that the PPy,P and PPy,W coated electrodes offered a noticeable enhancement in protection against corrosion processes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Synthesis and evaluation of ampicillin-conjugated gum arabic microspheres for sustained releaseJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 4 2007K. K. Nishi Ampicillin was conjugated to periodate-oxidized gum arabic (GA), a branched polysaccharide, to form the imino conjugate of the drug and the polysaccharide. The water-soluble conjugate was dispersed by sonication in a mixture of toluene and liquid paraffin in the presence of a non-ionic surfactant as droplet stabilizer and fabricated into microspheres by heat denaturation at 80°C to obtain spheres less than 2 ,m in diameter. These microspheres did not undergo dissolution in water on prolonged incubation. In-vitro release of ampicillin into phosphate buffer from the microspheres was slow and sustained with a cumulative release between 10 and 25% of the drug content in 10 days depending on the degree of oxidation of GA and the drug payload. Release into simulated gastric fluid was faster due to faster hydrolysis of the drug-GA bond in the acid medium, but when the medium was changed to intestinal fluid, the release was slowed down. Ampicillin released was functionally active and inhibited the growth of S. aureus and E. coli in cultures, although not as actively as free ampicillin. The microspheres underwent slow biodegradation on prolonged incubation in aqueous media. These studies show that ampicillin conjugated with oxidized GA and fabricated into microspheres possesses sustained-release characteristics for prolonged periods. [source] Kinetics and mechanism of oxidation of apple pectin by CrVI in aqueous acid medium,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2008Sebastián E. Bellú Abstract Selective oxidation of galacturonic acid residues of apple pectin by CrVI affords CO2/HCO2H, oxidized pectin, and CrIII as final redox products. The reaction shows first-order kinetics in [pectin], [CrVI], and [H+], at fixed ionic strength and temperature. Kinetic studies show that the redox reaction proceeds through a mechanism combining CrVI,,,CrIV,,,CrII and CrVI,,,CrIV,,,CrIII pathways. The mechanism is supported by the observation of free radicals, CrO (the formation of which implies involvement of CrII and CrIV) and CrV (formed in monoelectronic redox processes) as reaction intermediates. The reduction of CrIV and CrV by pectin was independently studied and found to occur more than 103 times faster than pectin,+,CrVI reaction, in acid medium. At pH 3,5, apple pectin,+,CrVI redox reaction is slow, oxo-chromate(V),pectin species stabilize and remain in solution during several hours. The present results show that these abundant and ubiquitous components of the cell walls of all land plants are able to reduce CrIV,VI or stabilize high-valent chromium depending on pH. Copyright © 2008 John Wiley & Sons, Ltd. [source] Impedance measurements on oxide films on aluminium obtained by pulsed tensionsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2003K. Belmokre Anodisation; Elektrochemische Impedanzspektroskopie (EIS); pulsierende Spannung; Alterung von Oxidfilmen Abstract We have performed this study on oxide films sealed or not in boiling water. The films are first obtained on type 1050 A aluminium substrat by pulsed tensions anodizing technique, in a sulfuric acid solution. Afterwards the, Electrochemical Impedance Spectroscopy (EIS) is employed to appreciate the films behaviour in a neutral solution of 3.5% K2SO4, in which the interface processes interest only the ageing phenomenon of the oxide films and not their corrosion. We have also attempted a correlation between pulse parameters of anodization and the electrical parameters characterizing these films. The sealing influence on ageing has been studied as well. For all films, ageing is appreciated using impedance diagrams evolution versus time. The results show: , the existence of two capacitive loops confirming the presence of two oxide layers characteristic of oxide films obtained in a sulfuric acid medium. The first loop, at high frequencies, is related to the external porous layer and the second one, at lower freqencies, is related to the internal barrier layer. , the thickness of the barrier layer varies between 25 and 40 nm in relation with the electrical pulse parameters. , the sealing acts favorably against anodic oxide films ageing. Impedanzmessungen an durch pulsierende Spannung erzeugten Oxidfilmen auf Aluminium Die vorliegenden Untersuchungen wurden an versiegelten und nicht versiegelten Oxidfilmen in kochendem Wasser durchgeführt. Die Filme wurden zuerst auf Aluminiumsubstrat des Typs 1050A durch anodische Technik mit pulsierender Spannung in einer Schwefelsäurelösung erzeugt. Anschließend wurde die elektrochemische Impedanzspektroskopie eingesetzt, um das Filmverhalten in einer neutralen 3,5% K2SO4 -Lösung zu beurteilen, wobei bezüglich der Grenzflächenprozesse nur das Alterungsphänomen der Oxidfilme und nicht ihr Korrosionsverhalten interessierte. Es wurde versucht, eine Korrelation zwischen den Pulsparametern der Anodisierung und den elektrischen Parametern, die diese Filme charakterisieren, zu finden. Ebenfalls wurde der Versiegelungseinfluss auf die Alterung untersucht. Für alle Filme wurde die Alterung mit Hilfe der Entwicklung von Impedanzdiagrammen über die Zeit beurteilt. Die Ergebnisse zeigen: , die Existenz von zwei kapazitiven Schleifen, die die Anwesenheit von zwei Oxidschichten bestätigen, was charakteristisch ist für Oxidfilme, die in einer Schwefelsäurelösung erzeugt wurden. Die erste Schleife, bei hohen Frequenzen, bezieht sich auf die äußere poröse Schicht und die zweite, bei niedrigeren Frequenzen, bezieht sich auf die innere Barriereschicht , die Dicke der Barriereschicht variiert zwischen 25 und 40 nm, abhängig von den elektrischen Pulsparametern , die Versiegelung wirkt günstig gegenüber der Alterung des anodischen Oxidfilms. [source] Surface passivation of GaInAsSb photodiodes with thioacetamidePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2007A. Salesse Abstract AlGaAsSb/GaInAsSb heterojunction mesa photodiodes having 2.2 µm cutoff wavelength, grown by MBE on (p) GaSb substrates, have been passivated using thioacetamide CH4CSNH2 and ammonium sulphide (NH4)2S. Superior characteristics were obtained from devices processed with thioacetamide in acid medium (pH = 2.4). At room temperature the surface leakage currents were suppressed, and the photodiodes showed R0A product as high as 16 ,cm2 and detectivity D* (2 µm, 0 V) , 1010 cm Hz1/2 W,1. A model explaining sulfuration mechanisms with thioacetamide and (NH4)2S is proposed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High salt-treatment-induced Na+ extrusion and low salt-treatment-induced Na+ accumulation in suspension-cultured cells of the mangrove plant, Bruguiera sexangulaPLANT CELL & ENVIRONMENT, Issue 10 2001M. Kura-Hotta Abstract A suspension-cultured cell strain of the mangrove plant (Bruguiera sexangula) was established from a callus culture and maintained in an amino acid medium in the absence of NaCl. NaCl non-adapted cells were transferred to media containing 0,200 mm NaCl. The initial growth rate decreased gradually with increasing salt concentrations. However, at up to 150 mm NaCl, cell number growth at the highest point was almost the same as that at lower salt concentrations. Cells even continued to grow in the presence of 200 mm NaCl. Cells incubated in a medium containing 50 mm NaCl for 3 weeks accumulated Na+, while those incubated in 150 mm NaCl for 2 d showed only a transient increase in Na+ and Cl, concentrations. In the latter treatment, the intracellular concentration of Na+ returned to the original low level within 2 weeks. It took a longer time for Cl, to return to its original level. As a result, the Na+ and Cl, concentrations in cells cultured with 50 mm NaCl were much larger than those in cells cultured with 150 mm NaCl. The intracellular distribution of ions after transfer to the medium containing 150 mm NaCl was analysed by isolating the vacuoles. Treatment with amiloride, an inhibitor of the Na+/H+ antiporter, suppressed the recovery of Na+ to the original level in the cells. Treatment with 150 mm NaCl for 3 d stimulated the activities of both the vanadate-dependent H+ -ATPase and the Na+/H+ antiporter in the plasma membrane fraction. [source] Nanocomposites of silver nanoparticle and dinonylnaphthalene disulfonic acid-doped thermoreversible polyaniline gelPOLYMER ENGINEERING & SCIENCE, Issue 3 2010Ashesh Garai Silver/polyaniline-dinonylnaphthalene disulfonic acid (PANI-DNNDSA) gel nanocomposites are prepared from the reduction of silver salt by polyaniline in formic acid medium. Scanning electron micrographs (SEM) indicate the presence of three-dimensional fibrillar network structure and the silver nanoparticles remain dispersed within the PANI-DNNDSA fibrillar network. Differential scanning calorimetric (DSC) study shows reversible first-order phase transition characterizing the composite to behave as a thermoreversible gel. Transmission electron micrographs (TEM) show a decrease of nanoparticle size with increasing AgNO3 concentration. Wide angle X-ray scattering (WAXS) patterns show lamellar structure in the gel as well as in the gel metal nanocomposites (GMNCs) and the two melting peaks in the DSC patterns correspond to the melting of monolayer and bilayer crystals produced from the interdigitation of DNNDSA tails anchored from PANI chains within the PANI lamella. The above melting points are greater in the GMNCs than that of pure gel indicating the formation of complex melting thermogram with crystallites produced from the anchored surfactants tails at the surface of Ag nanoparticles. The GMNCs show a higher thermal stability than that of pure PANI-DNNDSA gel. PANI-DNNDSA gel has an emission peak at 354 nm but fluorescence quenching occurs in the GMNCs and the emission peak becomes red shifted. Also in the UV,vis spectra the , band-polaron band transition peak shows a red shift and the DC conductivity increases with increasing Ag nanoparticle concentration in the GMNCs. The current (I),voltage (V) characteristic curves indicate Ohmic nature of conductivity of the gel and the current at the same voltage increases appreciably with increasing Ag nanoparticle concentration. These GMNCs are easily processible due to its thermoreversible nature. So, an easily processible, thermally stable and highly conducting DNNDSA-doped PANI-Ag gel nanocomposite with interesting photoluminescent property has been successfully developed suitable for optoelectronic applications. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] Aqueous polymerization of ethyl acrylate initiated by ceric ion-reducing agent systems in nitric acid mediumPOLYMER INTERNATIONAL, Issue 3 2001V Ramana Reddy Abstract Kinetic study of aqueous polymerization of ethyl acrylate (EA) was carried out at 30,°C in dilute nitric acid medium by employing ammonium ceric nitrate (ACN),methyl cellosolve (MC) and ACN,ethyl cellosolve (EC) as redox initiator systems. The ceric ion consumption was found to be first order with respect to ceric ion concentration with both initiator systems. The formation of complexes between Ce(IV) and reducing agents (RA) was observed. The order with respect to Ce(IV), reducing agents and monomer was evaluated for aqueous polymerization of EA by Ce(IV),MC and Ce(IV),EC redox initiator systems. The overall activation energy, Eoverall, for aqueous polymerization of EA was evaluated in the temperature region of 27,40,°C with both initiator systems. A kinetic mechanism for aqueous polymerization of EA initiated by redox initiator systems is presented. © 2001 Society of Chemical Industry [source] Facile High-Yield Synthesis of Polyaniline Nanosticks with Intrinsic Stability and Electrical ConductivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2008Xin-Gui Li Prof. Abstract Chemical oxidative polymerization at 15,°C was used for the simple and productive synthesis of polyaniline (PAN) nanosticks. The effect of polymerization media on the yield, size, stability, and electrical conductivity of the PAN nanosticks was studied by changing the concentration and nature of the acid medium and oxidant and by introducing organic solvent. Molecular and supramolecular structure, size, and size distribution of the PAN nanosticks were characterized by UV/Vis and IR spectroscopy, X-ray diffraction, laser particle-size analysis, and transmission electron microscopy. Introduction of organic solvent is advantageous for enhancing the yield of PAN nanosticks but disadvantageous for formation of PAN nanosticks with small size and high conductivity. The concentration and nature of the acid medium have a major influence on the polymerization yield and conductivity of the nanosized PAN. The average diameter and length of PAN nanosticks produced with 2,M HNO3 and 0.5,M H2SO4 as acid media are about 40 and 300,nm, respectively. The PAN nanosticks obtained in an optimal medium (i.e., 2,M HNO3) exhibit the highest conductivity of 2.23,S,cm,1 and the highest yield of 80.7,%. A mechanism of formation of nanosticks instead of nanoparticles is proposed. Nanocomposite films of the PAN nanosticks with poly(vinyl alcohol) show a low percolation threshold of 0.2,wt,%, at which the film retains almost the same transparency and strength as pure poly(vinyl alcohol) but 262,000 times the conductivity of pure poly(vinyl alcohol) film. The present synthesis of PAN nanosticks requires no external stabilizer and provides a facile and direct route for fabrication of PAN nanosticks with high yield, controllable size, intrinsic self-stability, strong redispersibility, high purity, and optimizable conductivity. [source] Synthesis and characterization of amphiphilic block copolymer of polyphosphoester and poly(L -lactic acid)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2008Xian-Zhu Yang Abstract Aliphatic polyesters and polyphosphoesters (PPEs) have received much interest in medical applications due to their favorable biocompatibility and biodegradability. In this work, novel amphiphilic triblock copolymers of PPE and poly(L -lactic acid) (PLLA) with various compositions were synthesized and characterized. The blocky structure was confirmed by GPC analyses. These triblock copolymers formed micelles composed of hydrophobic PLLA core and hydrophilic PPE shell in aqueous solution. Critical micellization concentrations of these triblock copolymers were related to the polymer compositions. Incubation of micelles at neutral pH followed by GPC analyses revealed that these polymer micelles were hydrolysized and resulted in decreased molecular weights and small oligomers, whereas its degradation in basic and acid mediums was accelerated. MTT assay also demonstrated the biocompatibility against HEK293 cells. These biodegradable polymers are potential as drug carriers for biomedical application. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6425,6434, 2008 [source] | |||||||||||||||||||