Search results for "Facta"
showing 10 items of 400 documents
Thermodynamical aspects regarding the formation of self-assembly decylpolyglucoside structures
2005
In this study, we used a generalized form of a recently reported parametrization based on the differential geometry and the thermodynamics of dispersed systems to ascertain the capability of decylpolyglucoside alone or in association with cholesterol to form vesicle structures (niosomes). The theoretical calculation of the energy balance involved in the vesicles formation was carried out using values of the critical concentration of formation (ccf), surface tension and the molar surface area of the non-ionic surfactant. Furthermore, in order to confirm the theoretical results found in this work, we prepared and characterized vesicles made with decylpolyglucoside and cholesterol. The vesicle…
Modulation of retention and selectivity in oil-in-water microemulsion liquid chromatography: A review
2019
Microemulsions (MEs) are stable, isotropically clear solutions consisting of an oil and water stabilized by a surfactant and a co-surfactant. Oil-in-water microemuslion liquid chromatography (MELC) is a relatively new chromatographic mode, which uses an O/W ME as mobile phase. Retention, selectivity and efficiency can be modified by changing the concentration of the ME components and the ratio between the aqueous and oil phases. This work makes a critical survey on the information found in the literature about the mobile phase compositions that lead to the creation of successful O/W ME mobile phases, as well as the effect of pH for ionizable compounds and temperature. The viability of perfo…
Physicochemical Investigation of Nanostructures in Liquid Phases: Ytterbium Nitrate Ionic Clusters Confined in Ytterbium Bis(2-ethylhexyl) Sulfosucci…
2007
The confinement of finite amounts of ytterbium nitrate in the nanoscopic space of ytterbium bis(2-ethylhexyl)sulfosuccinate (Yb(DEHSS) 3 ) reversed micelles dispersed in n-heptane has been investigated by UV-vis-NIR, FT-IR, and SAXS. The analysis of the experimental data is consistent with the hypothesis that Yb(NO 3 ) 3 is distributed among reversed micelles as small size ionic clusters surrounded by the Yb 3+ surfactant counterions and anionic heads while the surfactant alkyl chains point toward the solvent medium. As a consequence of confinement and interfacial effects, the ionic clusters display photophysical properties different from those in the bulk state or isolated species. Moreove…
Physicochemical Investigation of the Solubilization of Ytterbium Nitrate in AOT Reverse Micelles and Liquid Crystals
2006
A wide investigation of the solubilization of the water-soluble salt Yb(NO3)(3) in sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles and AOT liquid crystals has been carried out. After saturation of water/AOT/organic solvent w/o microemulsions with pure Yb(NO3)(3), the Yb(NO3)(3)/AOT composites were prepared by complete evaporation under vacuum of the volatile components (water and organic solvent) of the salt-containing microemulsions. It was observed that these composites can be totally dissolved in pure n-heptane or CCl4, allowing the solubilization of a noticeable amount of Yb(NO3)(3) in quite dry apolar media. By UV-vis-NIR, FT-IR, and H-1 NMR spectroscopies, some informati…
Synthesis of Yb nanoparticles by laser ablation of ytterbium target in sodium bis(2-ethylhexyl)sulfosuccinate reverse micellar solution
2010
Abstract Surfactant-coated ytterbium nanoparticles were produced by Nd:YAG laser ablation of a Yb bulk target immersed in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/ n -heptane micellar solution. In our experimental conditions, as highlighted by IR spectroscopy, AOT molecules are not decomposed by the intense laser pulses but play a pivotal role in the stabilisation of Yb nanoparticles. The formation of Yb nanoparticles in the liquid phase was monitored by UV–Vis spectroscopy whereas the Yb/AOT composites obtained by evaporation of the organic solvent were characterised by XPS and TEM. Data analysis consistently shows the presence of surfactant-coated, nearly spherical and non-interacting…
Etude de la biodisponibilité d'oligosaccharides éliciteurs dans les tissus foliaires en vue de l'amélioration de leur efficacité contre le mildiou de…
2015
Etude de la biodisponibilité d'oligosaccharides éliciteurs dans les tissus foliaires en vue de l'amélioration de leur efficacité contre le mildiou de la vigne
Passive sampling in monitoring of nonylphenol ethoxylates and nonylphenol in aquatic environments
2012
The present practices for determining the concentration levels of various pollutants are in many respects insufficient and for this reason, there is an urgent need especially to develop more cost-effective sampling methods. In this study, a novel passive sampling tool (the Chemcatcher®) for monitoring nonylphenol ethoxylates (NPEOs) and nonylphenol (NP) in aqueous media was tested. These environmentally harmful substances have been widely used in different household and industrial applications and they affect aquatic ecosystems, for example, by acting as endocrine disrupting compounds. The highest accumulation of NPEOs and NP in laboratory-scale tests was obtained when using an SDB-XC (stan…
Oil-In-Water Microemulsion Liquid Chromatography
2018
Oil-in-water microemulsions (O/W MEs) are obtained spontaneously by mixing two immiscible liquids (water and oil) in the presence of a surfactant. A co-surfactant is also often needed for ME stabil...
Polymerizable and polymeric zwitterionic surfactants: 1. Synthesis and bulk properties
1991
Abstract The synthesis of a series of permanently zwitterionic surfactant monomers based on sulphobetaines and the preparation of their polymers is described. Solubilities, thermal properties and bulk structures of the zwitterionic polymers are studied with respect to their molecular architecture, and compared with cationic analogues. The various solubilities of the polymers can be correlated with their molecular geometry, enabling differentiation into distinct classes. This behaviour is paralleled by the observed bulk structures of the polymers where distinct classes of superstructures are present. However, independently of the molecular geometry, no thermal transition could be detected fo…
Acid—base properties of azo dyes in the presence of surfactants
1991
Abstract The changes in the acid—base properties of an azo dye produced by the presence of surfactants, at surfactant concentrations below and above the CMC, are quantitatively described using a simple model and spectrophotometric and potentiometric measurements. The azo dye formed by aniline and N -(1-naphthyl)-ethylenediamine, and the surfactants sodium dodecyl sulphate, Triton X-100 and N -cetylpyridinium chloride (NCPC) are used. The protonation constants of the free and surfactant-bound dye species, the binding constant of the protonated and unprotonated forms of the dye, and the average aggregation number of the dye—NCPC aggregates are evaluated.