Chemical effects of cationic surfactant and anionic surfactant used in organically modified montmorillonites on degradation and fire retardancy of polyamide 12 nanocomposites

Three kinds of organically modified Na+-montmorillonites (OMMTs), including two kinds of octadecylammonium modified montmorillonite with different contents of octadecylammonium and a kind of sodium dodecylsulfonate (SDSo) modified montmorillonite, were used to prepare polyamide 12 (PA12)/OMMT nanocomposites. Effects of the modifiers on degradation and fire retardancy of PA12/OMMT nanocomposites were investigated. Acid sites formed in cationic surfactant modified MMT via Hoffman decomposition could accelerate degradation of PA12 at high temperature. However, catalytic effect of the acid sites on carbonization of the degradation products promoted char barrier formation, which reduced heat release rate (HRR). Higher content of cationic surfactant in OMMT is beneficial to fire retardancy of PA12 nanocomposites and the dispersion states of OMMT have assistant effects. In contrast, Na+-montmorillonite (Na-MMT) and anionic surfactant modified MMT (a-MMT) could not form acid sites on the MMT layers; in this case, fire retardancy of PA12/Na-MMT appears to have no improvement and PA12/a-MMT appears to have limited improvement.

Electrochemistry and electrochemiluminescence of stable tris(2,2 '-bipyridyl)ruthenium(II) monolayer assembled on benzene sulfonic acid modified glassy carbon electrode

An electrochemically stable monolayer of tris(2,2'-bipyridyl)ruthenium(II) was obtained for the first time. It was based on the electrostatic attachment of Ru(bpy)(3)(2+) to the benzene sulfonic acid monolayer film, which was covalently bound onto glassy carbon electrode by the electrochemical reduction of diazobenzene sulfonic acid. The surface-confined Ru(bpy)(3)(2+) underwent reversible surface process, and reacted with the coreactant, tripropylamine, to produce electrochemiluminescence. In view of the stability of the electrode, the results strongly suggested that light was emitted from the surface-confined Ru(bpy)(3)(2+), not from the detached Ru(bpy)(3)(2+). The Ru(bpy)(3)(2+) modified electrode was used to the determination of tripropylamine. It showed good linearity in the concentration range from 5 muM to 1 muM with a detection limit of 1 muM (S/N = 4). The good stability of the Ru(bpy)(3)(2+) modified electrode also showed that the benzene sulfonic acid monolayer film prepared can be served as an excellent support to construct multilayers. (C) 2001 Elsevier Science B.V. All rights reserved.

The problem of purity in evaluating surfactant performance

Labeled surfactants have impurities in the form of un-reacted molecules or distributed products which is a constraint in evaluating its performance. This short review deals with the purity issue of surfactants and is divided into two parts. The first part deals with the methods of purification employed for obtaining a surface chemically pure surfactant for evaluation. In the second part the use of surface chemically impure surfactant in application areas of formulations is presented to highlight the impending impact on reproducibility of results.

An infrared study of adsorption of paranitrophenol on mono, di and trialkyl surfactant intercalated organoclays

Infrared spectroscopy has been used to study the adsorption of paranitrophenol on mono, di and tri alkyl surfactant intercalated montmorillonite. Organoclays were obtained by the cationic exchange of mono, di and tri alkyl chain surfactants for sodium ions [hexadecyltrimethylammonium bromide (HDTMAB), dimethyldioctadecylammonium bromide (DDOAB), methyltrioctadecylammonium bromide (MTOAB)] in an aqueous solution with Na-montmorillonite. Upon formation of the organoclay, the properties change from strongly hydrophilic to strongly hydrophobic. This change in surface properties is observed by a decrease in intensity of the OH stretching vibrations assigned to water in the cation hydration sphere of the montmorillonite. As the cation is replaced by the surfactant molecules the paranitrophenol replaces the surfactant molecules in the clay interlayer. Bands attributed to CH stretching and bending vibrations change for the surfactant intercalated montmorillonite. Strong changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surface. This study demonstrates that paranitrophenol will penetrate into the untreated clay interlayer and replace the intercalated surfactant in surfactant modified clay, resulting in the change of the arrangement of the intercalated surfactant.

Reduction of functionalized graphite oxides by trioctylphosphine in non-polar organic solvents

Graphene, functionalized with oleylamine (OA) and soluble in non-polar organic solvents, was produced on a large scale with a high yield by combining the Hummers process for graphite oxidation, an amine-coupling process to make OA-functionalized graphite oxide (OA-GO), and a novel reduction process using trioctylphosphine (TOP). TOP acts as both a reducing agent and an aggregation-prevention surfactant in the reduction of OA-GO in 1,2-dichlorobenzene (DCB). The reduction of OA-GO is confirmed by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and Raman spectroscopy. The exfoliation of GO, OA GO, and OA-functionalized graphene (OA-G) is verified by atomic force microscopy. The conductivity of TOP-reduced OA G, which is deduced from the current–voltage characteristics of a vacuum-filtered thin film, shows that the reduction of functionalized GO by TOP is as effective as the reduction of GO by hydrazine.

Comparison of nanostructures obtained from galvanic replacement in water and an ionic liquid for applications in electrocatalysis and SERS

We demonstrate potential applications for unusual dendrite like Au–Ag alloy nanoparticles formed via a galvanic replacement reaction in the ionic liquid [BMIM][BF4]. In comparison to Au–Ag alloy nanoshells synthesised via a similar reaction in water, the unusual branched structure of the dendritic materials led to increased electrocatalytic activity for the oxidation of both formaldehyde and hydrazine, and increased sensitivity and spectral resolution for the surface enhanced Raman scattering (SERS) of 4,4-bipyridal.

Insoluble anode of porous lead dioxide for electrosynthesis: preparation and characterization

Preparation of a novel type of titanium-substrate lead dioxide anode with enhanced electrocatalytic activity for electrosynthesis is described. It has been demonstrated that in the presence of a suitable surfactant in the coating solution, an adherent and mainly tetragonal form of lead dioxide is deposited on a platinized titanium surface such that the solution side of the coating is porous while the substrate side is compact. By an analysis of anodic charging curves and steady-state Tafel plots with such porous electrodes in contact with sodium sulphate solution, it has been proved that the electrochemically active area of these anodes is higher by more than an order of magnitude when compared to the area of conventional titanium-substrate lead dioxide anodes. The electrocatalytic activity is also thereby enhanced to a significant degree.

Enhancing the mesoporosity of pillared clay catalyst - a study of pillar aggregates and deactivation in alkylation reaction

A sample of montmorillonite was pillared with aluminium polyoxycations in presence of different amounts of tween-80, a nonionic surfactant, ranging from 0.01 to 0.20 mmol/meq of clay. The amount of aluminium sorbed was found to vary with the amount of surfactant added during pillaring. Vapour phase catalytic activity of the samples for alkylation of toluene with methanol in a fixed bed down flow reactor showed that the rate of deactivation, in general, increased with decrease in the pillar density. The samples treated with 0.06 to 0.08 mmol/meq of surfactant showed the lowest deactivation and also an enhancement in the mesopores which did not change on calcining to 540°C. Suppression of deactivation is attributed to the distribution of pillars by the surfactant in such a way as to decrease the coke formation.

Contrast in luminescence characteristics (intense UV to bright visible light) of ZnO nanostructures with the variation in microstructure

We report the controlled variation of luminescence of ZnO nanostructures from intense ultraviolet to bright visible light. Deliberate addition of surfactants in the reaction medium not only leads to growth anisotropy of ZnO, but also alters the luminescence property. ZnO nanoclusters comprising of very fine particles with crystallite sizes approximate to 15-22nm were prepared in a non-aqueous medium, either from a single alcohol or from their mixtures. Introduction of the aqueous solution of the surfactant helps in altering the microstructure of ZnO nanostructure to nanorods, nanodumb-bells as well as the luminescence property. The as-prepared powder material is found to be well crystallized. Defects introduced by the surfactant in aqueous medium play an important role in substantial transition in the optical luminescence. Chromaticity coordinates were found to lie in the yellow region of color space. This gives an impression of white light emission from ZnO nanocrystals, when excited by a blue laser. Oxygen vacancy is described as the major defect responsible for visible light emission as quantified by X-ray photoelectron spectroscopy and Raman analysis.

Vertical variation in dissolved alkaline phosphatase activity in a shallow eutrophic lake determined in reverse micelles

We evaluated the feasibility of microencapsulating dissolved alkaline phosphatase of a water body into reverse micelle systems prepared by hexadecyltrimethylammonium bromide as a surfactant in cyclohexane and 1-butanol as co-surfactant. The dissolved alkaline phosphatase activity within the micelle was described, including its kinetic parameters and the effects of pH and temperature on catalytic activity in surface, overlying and interstitial water of Lake Donghu. We found the similarities on the behavior of dissolved alkaline phosphatase of surface and interstitial water in reverse micelles, which was distinctly different from its behavior in the overlying water. This difference likely reflected the different origins of the dissolved alkaline phosphatase in the vertical profile of the lake. This system provides a novel tool with which to study the diversity and ecological significance of extracellular enzymes in aquatic environments.

Micelle-assisted synthesis of polyaniline/magnetite nanorods by in situ self-assembly process

Polyaniline/magnetite nanocomposites consisting of polyaniline (PANI) nanorods surrounded by magnetite nanoparticles were prepared via an in situ self-assembly process in the presence of PANI nanorods. The synthesis is based on the well-known chemical oxidative polymerization of aniline in an acidic environment, with ammonium persulfate (APS) as the oxidant. An organic acid (dodecylbenzenesulfonic acid, DBSA) was used to replace the conventional strong acidic (1 M HCl) environment. Here, dodecylbenzenesulfonic acid is used not only as dopant, but also as surfactant in our reaction system.

Dissolved Argon Changes the Rate of Diffusion in Room Temperature Ionic Liquids: Effect of the Presence and Absence of Argon and Nitrogen on the Voltammetry of Ferrocene

This work explores the effects of argon and nitrogen, two electrochemically and chemically inert gases frequently used in sample preparation of room temperature ionic liquid (RTIL) solutions, on the eelectrochemical characterization of ferrocene (Fc) dissolved in the RTIL 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C(2)mim][NTf2]). Remarkably, chronoamperometrically determined diffusion coefficients of Fc in [C(2)mim][NTf2] are found to increase from 4.8 (+/- 0.2) x 10(-11) m(2) s(-1) under vacuum conditions to 6.6 (+/- 0.5) x 10(-11) m(2) s(-1) in an atmosphere of 1 atm Ar. In contrast, exposing a vacuum-purified sample to an atmosphere of 1 atm N-2 resulted in no significant change in the measured diffusion coefficient of Fc. The effect of dissolved argon on diffusion transport is unexpected and has implications in electrochemistry and elsewhere. Fc was found to volatilize under vacuum conditions. We propose, however, that evacuation of the cell by vacuum prior to electrochemical measurements being carried out is the only way to ensure that no contamination of the sample occurs, and use of an in situ method of determining the diffusion coefficient and concentration of Fc dispells,any ambiguity associated with Fc depletion by vacuum.

Pressure-dependent product distribution of citral hydrogenation over micelle-hosted Pd and Ru nanoparticles in supercritical carbon dioxide

In situ synthesis and testing of Ru and Pd nanoparticles as catalysts in the presence of ammonium perfluorohydrocarbo-carboxylate surfactant in supercritical carbon dioxide were carried out in a stainless steel batch reactor at 40 degrees C over a pressure range of 80-150 bar CO2/H-2. Direct Visualization of the formation of a supercritical phase at above 80 bar, followed by the formation of homogeneous microemulsions containing dispersed Ru nanoparticles and Pd nanoparticles in scCO(2) at above 95-100 bar, were conducted through a sapphire window reactor using a W-0 (molar water to surfactant ratio) of 30. The synthesised RU and Pd nanoparticles showed interesting product distributions in the selective hydrogenation of organic molecules, depending critically oil the density and polarity of the fluid (which ill turn depends on the pressure applied). Thus, selective hydrogenation of the citral molecule, which contains three reducible groups (aldehydes and double bonds at the 23 and 6,7 positions), is feasible Lis a chemical probe. (c) 2005 Elsevier Inc. All rights reserved.

Recovery of lactoferrin and lactoperoxidase from sweet whey using colloidal gas aphrons (CGAs) generated from an anionic surfactant, AOT

The recovery of lactoferrin and lactoperoxidase from sweet whey was studied using colloidal gas aphrons (CGAs), which are surfactant-stabilized microbubbles (10-100 mum). CGAs are generated by intense stirring (8000 rpm for 10 min) of the anionic surfactant AOT (sodium bis-2-ethylhexyl sulfosuccinate). A volume of CGAs (10-30 mL) is mixed with a given volume of whey (1 - 10 mL), and the mixture is allowed to separate into two phases: the aphron (top) phase and the liquid (bottom) phase. Each of the phases is analyzed by SDS-PAGE and surfactant colorimetric assay. A statistical experimental design has been developed to assess the effect of different process parameters including pH, ionic strength, the concentration of surfactant in the CGAs generating solution, the volume of CGAs and the volume of whey on separation efficiency. As expected pH, ionic strength and the volume of whey (i.e. the amount of total protein in the starting material) are the main factors influencing the partitioning of the Lf(.)Lp fraction into the aphron phase. Moreover, it has been demonstrated that best separation performance was achieved at pH = 4 and ionic strength = 0.1 mol/L i.e., with conditions favoring electrostatic interactions between target proteins and CGAs (recovery was 90% and the concentration of lactoferrin and lactoperoxidase in the aphron phase was 25 times higher than that in the liquid phase), whereas conditions favoring hydrophobic interactions (pH close to pI and high ionic strength) led to lower performance. However, under these conditions, as confirmed by zeta potential measurements, the adsorption of both target proteins and contaminant proteins is favored. Thus, low selectivity is achieved at all of the studied conditions. These results confirm the initial hypothesis that CGAs act as ion exchangers and that the selectivity of the process can be manipulated by changing main operating parameters such as type of surfactant, pH and ionic strength.

Interaction of giant extracellular Glossoscolex paulistus hemoglobin (HbGp) with zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS): Effects of oligomeric dissociation

The present work focuses on the interaction between the zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp). Electronic optical absorption, fluorescence emission and circular dichroism spectroscopy techniques, together with Gel-filtration chromatography, were used in order to evaluate the oligomeric dissociation as well as the autoxidation of HbGp as a function of the interaction with HPS. A peculiar behavior was observed for the HPS-HbGp interaction: a complex ferric species formation equilibrium was promoted, as a consequence of the autoxidation and oligomeric dissociation processes. At pH 7.0, HPS is more effective up to 1 mM while at pH 9.0 the surfactant effect is more intense above 1 mM. Furthermore, the interaction of HPS with HbGp was clearly less intense than the interaction of this hemoglobin with cationic (CTAC) and anionic (SDS) surfactants. Probably, this lower interaction with HPS is due to two factors: (i) the lower electrostatic attraction between the HPS surfactant and the protein surface ionic sites when compared to the electrostatic interaction between HbGp and cationic and anionic surfactants, and (ii) the low cmc of HPS, which probably reduces the interaction of the surfactant in the monomeric form with the protein. The present work emphasizes the importance of the electrostatic contribution in the interaction between ionic surfactants and HbGp. Furthermore, in the whole HPS concentration range used in this study, no folding and autoxidation decrease induced by this surfactant were observed. This is quite different from the literature data on the interaction between surfactants and tetrameric hemoglobins, that supports the occurrence of this behavior for the intracellular hemoglobins at low surfactant concentration range. Spectroscopic data are discussed and compared with the literature in order to improve the understanding of hemoglobin-surfactant interaction as well as the acid isoelectric point (pI) influence of the giant extracellular hemoglobins on their structure-activity relationship. (c) 2007 Elsevier B.V. All rights reserved.