Fundamental studies of mixed-gas inductively coupled plasmas

The effects of adding foreign gases to the central-gas flow or the intermediate-gas flow of an argon inductively coupled plasma are presented. In particular, the influence of up to 16.7% added helium, nitrogen or hydrogen on radially-resolved electron number density, electron temperature, gas-kinetic temperature and calcium ion emission profiles is examined. It is shown that these gases affect not only the fundamental parameters and bulk properties of the plasma, but also how energy is coupled and transported through the discharge and how that energy interacts with the sample. For example, added helium causes an increase in the gas-kinetic temperature, most likely due to the higher thermal conductivity of helium compared to argon but, in general, does not appear to affect significantly either the electron temperature or electron concentration. The shift in the calcium ion emission profile towards lower regions in the discharge with added helium may be attributable to higher droplet desolvation and particle vaporization rates. In contrast, the addition of nitrogen or hydrogen to an Inductively Coupled Argon Plasma (Ar ICP) results in dramatic changes in all three fundamental plasma parameters: electron number density, electron temperature, and gas-kinetic temperature. The net effect of these molecular gases (N₂ or H₂) on calcium ion emission and on the fundamental plasma parameters is shown to be dependent on the amount of gas added to the plasma and whether the gas is introduced as part of the central- or intermediate-gas flow. In general, nitrogen added to the central-gas flow causes a significant reduction in the number of electrons throughout most of the discharge (over an order of magnitude in certain regions), mainly in the central and upper zones of the ICP. A drop of 3000–5000 K in the central channel electron temperature and a smaller drop in the gas-kinetic temperature are also observed when N₂ is added to the central-gas flow. In contrast, the introduction of nitrogen in the intermediate flow causes about a 1 × 10¹⁵ electrons cm⁻³ increase in the electron concentration in the low, toroidal regions of the plasma and an increase in the gas-kinetic temperature of around 1000 K throughout most of the discharge. As seen with the addition of nitrogen to the central-gas flow, the electron temperature is found to increase in the toroidal zones of the plasma when N₂ is added to the intermediate flow. These combined effects cause a 20-fold depression in the calcium ion emission intensity only a 1.7-fold depression when N₂ is added to the central- or intermediate-gas flows, respectively. On the other hand, hydrogen causes a depression in the electron concentration in the upper areas of the plasma when this gas is added to the central flow but increases the number of electrons in the same region when added to the intermediate flow. Hydrogen also causes a dramatic effect on the electron and gas-kinetic temperatures, significantly increasing both of these parameters throughout the discharge. An increase in the calcium ion emission intensity, accompanied by a downward shift, elongation and broadening of the calcium ion emission profile is also observed with H₂ addition.     

Physico-chemical forms of radiostrontium in simulated freshwaters

A method for the analysis of the physico-chemical forms of radiostrontium in waters is described and applied to the simulated lake and groundwaters to which were later added clay minerals and humus substances. The simulated water samples were fractionated using filtration and ultrafiltration: particulates, colloids and dissolved species. The dissolved species were further separated into three fractions using ion exchange: cations, anions and non-ionic species. The physico-chemical forms of radiostrontium do not appreciable change when humus substances or clay mineral or both are added to the water samples. Only about 1–6% of added radiostrontium was found in particulate and colloid fractions. The greatest amount of⁸⁵Sr was always found in the dissolved fraction, cations (>87%). Radiostrontium was never found in the dissolved fraction, anions or non-ionic species.     

Gamma Radiation-Induced Template Polymerization of Acrylic Acid in the Presence of Polyactrylamide

Abstract

Poly(acrylamide-acrylic acid) resin p(AM-AA) was prepared by gamma radiation-induced polymerization of acrylic acid in the presence of polyacrylamide as a template polymer. The polymerization was studied by a free radical mechanism at different experimental conditions such as: absorbed dose, monomer concentration, polymer/monomer molar ratio and the weight-average molecular weight or the swelling degree of added polymer. The resin was obtained at dose > 10 KGy and there is no significant change in the swelling degree of the resin. The results showed that the capacity of the resin increases by increasing the monomer concentration, the weight-average molecular weight of the added polymer and decreases by increasing polymer/monomer molar ratio and the swelling degree of the added polymer. It was also found that the capacity of the resin depends on the radiation dose.     

Effect of sodium metasilicate on natural flotability of coal

The effect of the quantity of sodium metasilicate and conditioning time in one set of experiments, and the effect of the solution concentration of sodium metasilicate, added at the same dosage and conditioning time to coal slurry, on flotability of a typical Indian coal in another set of experiments are studied. Two sets of 3² full factorial experiments are carried out to assess the effects of the aforementioned variables. The generated data are analyzed quantitatively and explained qualitatively. At 0.1% (w/v) solution concentration of solution added (0.02 g/kg) and 8 min conditioning time, sodium metasilicate acted as activator for kaolinite, whereas at 1.0% (w/v) solution concentration (0.2 g/kg), it acted as dispersant. The best observed condition of depressant is obtained at an added concentration of 10.0% (w/v, 0.2 g/kg) and 8 min conditioning time. The desired effect of the sodium metasilicate can be achieved by controlling its quantity, solution concentration added, and conditioning time.     

Chloroplatinic acid catalyzed additions of silanes to isoprene

The chloroplatinic acid catalyzed hydrosilylation of isoprene with trichlorodichloromethyl-, and trimethylsilane has been reinvestigated with the purpose of establishing the mode of addition to the substrate. This was accomplished by identifying the structures of the $\text{1}\text{1}$ adducts, their methylated derivatives and the saturated analogs of the latter. Trichlorosilane added 1,4 to the less hindered side of isoprene; dichloromethylsilane added both 1,2 and 1,4 to the less hindered side and trimethylsilane added 1,2 and 1,4 to both sides of isoprene. These results are contrary to those previously reported in the literature.     

Inorganic Salts Trapped in Neutral Carrier Ion-Selective Electrode Membranes form Ion-Exchange Sites

Abstract

Deliberately added hydrophilic salt contaminations behave as ion-exchange sites in the plasticized PVC membrane of a neutral carrier ion-selective electrode. The added salt does not influence the potenticmetric performance of the membrane. Since the membrane without added salt is itself an ion-exchanger, its ion-exchange capacity may be linked to ionizable hydrophilic impurities.     

Graft Copolymerization of Vinyl Monomers onto Silk Fibers

Modification of the properties of textile fibers in order to get a fiber of improved textile performance is the subject of study of several groups of scientists and technologists [1–4]. Of the several methods available, grafting promises to be a potentially effective means of altering the fiber properties through the added polymer formed in situ without destroying the basic properties of the parent fiber. Copolymerization is attractive to chemists as a means of modifying macromolecules since, in general, degradation can be minimized. The desirable properties of the polymer are retained and copolymerization provides additional properties through the added polymer. The added polymer may be formed in situ by polymerization of a monomer or monomers, by condensation of reactants, or by the deposition of preformed polymer.     

Structural transformations in macromolecules of synthetic nonionogenic polymers and DNA in salt-containing aqueous solutions

The influence of salt additives on structural transformations in macromolecules of synthetic polymers free of ionogenic groups and DNA molecules has been determined with the use of the nanosecond dynamics luminescent method. When polyvalent metal salts are added, a coil-globule transition is observed in macromolecules of poly(N-n-propylmethacrylamide), while structural transformations occur in DNA macromolecules in aqueous solutions, processes that are accompanied by the passage of low-molecular-mass organic cations intercalated into DNA into solution. These transformations make themselves evident when polyvalent metal ions are added in an amount of one Mt³⁺ ion per ten phosphate groups of DNA. The same effect takes place when salts of polycations are added to solutions of DNA-polycation interpolyelectrolyte complexes.     

Preparation of TiO2 Sol Using TiCl4 as a Precursor

A titanium dioxide sol with narrow particle size distribution was synthesized using TiCl₄ as the starting material. The sol was prepared by a process where HCl was added to a gel of hydrated titanium oxide to dissolve it. The resulting aqueous titanic acid solution was heated to form titanium dioxide sol. The effects of preparation parameters were investigated. TiCl₄ was slowly added to distilled water at 5°C. Aqueous solution of sodium hydroxide was added to adjust the pH of the system to 8–12. After aging for a period of time, the peptized sol was filtered and sufficiently washed. The filtered cake was repulped in water. Hydrochloric acid was slowly added to the solution with stirring. After condensation reaction and crystallization, a transparent sol with suspended TiO₂ was formed. XRD results show that the crystalline phase was anatase. The suspended TiO₂ particles were rhombus primary particles with the major axis ca. 20 nm and the minor axis ca. 5 nm. The TiO₂ particles prepared at pH 8 had the largest surface area of 141 cm³/g and it was microporous. The compositions of the solution which yielded the smallest suspended TiO₂ particles were TiO₂:HCl (35% HCl) = 1:1 (molar ratio), concentration of TiO₂ = 10%. Hydroxypropyl cellulose with viscosity of 150–400 cps was added as a dispersant. The sol was excellent in dispersibility and long-term stability. Transparent thin films could be obtained through dip-coating glass substrate in the sol. The dip-coating on glass can be less than three times to have one monolayer TiO₂. The transparent TiO₂ thin film had strong hydrophilicity after being illuminated by UV light.     

A comparison between the SBR vulcanizates reinforced by magnesium methacrylate added directly or prepared in situ

The styrene-butadiene rubber (SBR) cured by dicumyl peroxide was reinforced by magnesium methacrylate [Mg(MAA)₂], which was added into SBR directly or prepared in situ in SBR through the neutralization of magnesium oxide (MgO) and methacrylic acid (MAA). The experimental results show that the SBR vulcanizates reinforced by Mg(MAA)₂ prepared in situ have better mechanical properties than those reinforced by Mg(MAA)₂ added directly. The SBR vulcanizates with Mg(MAA)₂ prepared in situ are semi-transparent, but those with Mg(MAA)₂ added directly are opaque. The Fourier transform infrared analysis shows that the polymerization conversion of Mg(MAA)₂ in the SBR vulcanizates with Mg(MAA)₂ prepared in situ is much higher than that in the SBR vulcanizates with Mg(MAA)₂ added directly. The scan probe microscopy photographs show that the particles in the SBR vulcanizates with Mg(MAA)₂ prepared in situ are much finer and disperse more evenly than that in the SBR vulcanizates with Mg(MAA)₂ added directly.     

Kinetic aspects of styrene minisuspension polymerization using a mixture PVA-SDS as stabilizer: Effect of the time of addition of SDS

The styrene minisuspension polymerization at 70 °C using AIBN as initiator and Polyvinil alcohol (PVA) and mixture PVA-sodium dodecil sulfate (SDS) as stabilizers was studied focusing on the kinetic behavior of the process after the SDS was added (PVA is present from the beginning and SDS is added at a given time t_SDS). It was confirmed that the addition of SDS to the system initially stabilized with PVA highly enhances the colloidal stability of the polymer particles because of the association formed between SDS and PVA molecules. It was observed that when SDS is added the rate of polymerization, the average molecular weight and final latex viscosity increase. The earlier the addition of SDS the more marked these increments. This behavior is explained in terms of the colloidal stability of the particles formed via emulsion polymerization and its effect on kinetic aspects such as the evolution of molecular weight and particle size distributions during the minisuspension polymerization.     

Swelling of Water/Nonionic Surfactant Lamellar Liquid Crystals: A Model

A model is presented to provide quantitative measures to estimate the trends of the change in the penetration of the added component into the polar part of the amphiphile layer in lamellar liquid crystals of water and ethoxylated surfactants with added water (or polar solvents). The total thickness of the bi‐layer is treated as composed of an aqueous layer, of a layer of the polar groups from the surfactant and of the hydrocarbon chains of the latter. A fraction α of the added water is assumed penetrating the polar group layer leading to its expansion. The evaluation is built on the fact that experimental determinations of the interlayer spacing in the overwhelming majority of cases show a first order linear dependence on the ratio of added water. In the model this linearity is obtained by variation of the degree of penetration of water. The model indicated a reduction in the degree of penetration with added water, which is a rational trend. The model demonstrates the earlier interpretation of a structure, whose interlayer spacing is invariant with water contents as nonswelling; for example, in which all added water penetrates the amhiphile layer, is not appropriate. The model demonstrates the constancy of the interlayer spacing to be a consequence of a balance between the expansion of the amphiphile layer and the increase of a “free water” layer.     

Determination of some organic thio-compounds by precipitation of mercuric sulphide from mercury(II) ammine complexes-I Determination of thioacetamide and thioacetanilide

A gravimetric method based on precipitation of mercuric sulphide has been developed for determining thioacetamide and thioacetanilide. Concentrated nitric acid is added to 0.1M mercuric nitrate, the solution is made alkaline with concentrated ammonia solution, and thioacetamide (dissolved in water) or thioacetanilide (dissolved in alcohol) is added, and the mixture is boiled. The method has good accuracy, and takes about 40 min.     

Improved Hiyama cross-coupling reactions using HOMSi® reagents: a novel application of a palladacycle

Various parameters in the Hiyama cross-coupling reaction of HOMSi® reagents with ethyl bromobenzoate were studied. These included solvent, ligand, palladium source, and added water. DMF and THF were found to be excellent solvents. Palladium chloride was found to be the best palladium source and no added water was required. The use of tri-o-tolylphosphine as the ligand proved to be particularly effective.     

Effect of Added Pyridine Bases on the Electron Transfer Reaction of Chromium(VI) with Organic Sulfides. Spectral Evidence for the Formation of a Chromium(V) Intermediate

The electron transfer reaction of Cr(VI) with organic sulfides is facilitated by added pyridine bases 2,2′-bipyridine, 1,10-phenanthroline, picolinic acid and pyridine 2,6-dicarboxylic acid. The added base forms a Cr(VI)-base adduct carrying positive charge which acts as a more reactive oxidant compared to Cr(VI). UV–Visible spectrophotometric study provides evidence for the formation of Cr(V) as the intermediate. The reactions in the absence and presence of pyridine bases follow the reactivity–selectivity principle.     

Recent advances of use of the supercritical carbon dioxide for the biomass pre-treatment and extraction: A mini-review

Biomass is considered as the most sustainable and renewable resource for the synthesis of value added potential platform chemicals. Various techniques are utilized to extract or to pre-treat or to isolate various value added chemicals from biomass. Pre-treatment of the biomass is a very essential aspect to enhance the biomass processing yield which is attributed to reduced lignin content/delignification, cellulose crystallinity and hemi-cellulose hydration. In search of efficient extraction and processing for biomass treatment, supercritical fluid (SCF) has been considered as the green technique to obtain the value added chemicals with higher efficiency than conventional technique. The use of the supercritical carbon dioxide (SC–CO₂) pre-treatment on biomass not only enhances glucose yield effectively but also delignify, hydrolyse hemi-cellulose component and allows extraction of various compounds from the biomass. However, very limited research articles are available for the use of SC-CO₂ for biomass processing to obtain value-added chemicals. In view of this, the present review article focus on the recent advances of applications of SC-CO₂ in (i) extraction of value added chemicals from biomass processing, (ii) biomass pre-treatment, (iii) factors affecting SC-CO₂ processing efficiency, (iv) scale-up scenario (v) challenges and opportunities in this field.     

Effect of alcohols on the micellar properties in aqueous solution of alkyltrimethylammonium bromides

The effect ofn-butanol,n-propanol, andn-hexanol on the critical micelle concentration (CMC) and degree of ionisation of the micelles of dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromides in aqueous solution has been determined by conductimetric techniques. Increase of the molality of added alcohol over the concentration ranges examined (up to 0.3 mol kg^–1 butanol, 0.07 mol kg^–1 pentanol and 0.025 mol kg^–1 hexanol) caused a progressive decrease of CMC and increase of the degree of ionisation for each surfactant-alcohol system. At a constant molality of added alcohol the degree of ionisation increased with a) an increase of the chain length of the surfactant for each alcohol and b) an increase of the chain length of the alcohol for each surfactant. The distribution of each alcohol between the aqueous and micellar phases and the free energy of solubilization were determined from the change of CMC with molality of added alcohol.     

Shift of reaction pathway by added chloride ions in the oxidation of aromatic ketones by dichloroisocyanuric acid—A kinetic study

Role of added chloride ions on the shift of reaction pathway of oxidation of aromatic ketones (acetophenone, desoxybenzoin) by dichloroisocyanuric acid (DCICA) was studied in aqueous acetic acid—perchloric acid medium. Participation of enolic and protonated forms of ketones in the rate determining steps is manifested from zero and first orders with respect to the oxidant in absence and presence of added chloride ions, respectively. Positive and negative effects of acid and dielectric constant on the reaction rate were observed. The observations deduce plausible mechanisms involving (i) rate-determining formation of enol from the conjugate acid of the ketone (SH⁺) in the absence of added chloride ions and (ii) rapid formation of molecular chlorine species from HOCl (hydrolytic species of DCICA) in the presence of added chloride ions, which then interacts with SH⁺ in a rate-determining step prior to the rapid steps of product formation. The order of Arrhenius parameters substantiate the proposed plausible mechanisms based on order of reactants both in presence and absence of added chloride ions.     

Quenching of fluorescence from pyrene in micellar solutions by cationic quenchers

The fluorescence from the S₁ state of pyrene solubilized within the hydrophobic region of sodium dodecyl sulfate micelles has been studied as a function of concentration of some cationic additives to the aqueous phase. At concentrations of added quencher below ca. 10^?3 mol dm^?3 the fluorescence decay follows a complex rate law; at long time, the decay is exponential with the same time constant as that of pyrene (S₁) without added quencher. The initial slope of the decay curve depends linearly on the concentration of added cation. These results are discussed in terms of the recently proposed model which requires the water-hydrocarbon interface to penetrate the micelle in the region of the probe. An analytical treatment is presented which, on the premises stated, serves to explain the observed kinetic features.     

Influence of free protein on flocculation stability of beta-lactoglobulin stabilized oil-in-water emulsions at neutral pH and ambient temperature

The influence of protein concentration and order of addition relative to homogenization (before or after) on the extent of droplet flocculation in oil-in-water emulsions stabilized by a globular protein was examined using laser diffraction. n-Hexadecane (10 wt%) oil-in-water emulsions (pH 7, 150 mM NaCl) stabilized by beta-lactoglobulin (beta-Lg) were prepared by three methods: (1) 4 mg/mL beta-Lg added before homogenization; (2)10 mg/mL beta-Lg added before homogenization; (3) 4 mg/mL beta-Lg added before homogenization and 6 mg/mL beta-Lg added after homogenization. Emulsion 1 contained little nonadsorbed protein (<3%) and underwent extremely rapid and extensive droplet flocculation immediately after homogenization. Emulsion 2 contained a significant fraction of nonadsorbed beta-Lg and exhibited relatively slow droplet flocculation for some hours after homogenization. Measurements on Emulsion 3 showed that the extremely rapid particle growth observed in Emulsion 1 could be arrested by adding native beta-Lg immediately after homogenization. The extent of particle growth in the three types of emulsions was highly dependent on the time that the salt was added to the emulsions, i.e., after 0 or 24 h aging. We postulate that the observed differences are due to changes in droplet surface hydrophobicity caused by differences in the packing or conformation of adsorbed proteins. Our data suggest that history effects have a strong influence on the flocculation stability of protein-stabilized emulsions, which has important implications for the formulation and production of protein stabilized oil-in-water emulsions.