The aggregation of the sodium dodecyl sulfate –n - octanol–water system at low concentration

Micelle formation in sodium dodecyl sulfate (SDS)–n-octanol mixtures was studied by several techniques and the results were interpreted using regular solution theory for mixed-micelle formation. Octanol was considered as a nonionic surfactant. The composition of micelles at the critical micelle concentration (cmc) was computed together with the interaction parameter and the activity coefficient of the components of the micelles. The fluorescence quenching technique with pyrene was employed to obtain the SDS and octanol aggregation numbers at the cmc. The results were in agreement with similar studies on other alcohol–SDS systems. At the cmc spherical, almost fully ionized micelles formed, while at a higher concentration there was a transition to anisometric (probably rodlike) micelles which pushed sodium counterions into their Stern double layer. Mixed anisometric micelles were more ionized than pure SDS micelles. When the octanol:SDS total ratio exceeded 0.85:1, an emulsion of octanol appeared in equilibrium with the micelles. Received: 23 December 1998 Accepted in revised form: 3 March 1999     

Exploring the Limits of Emulsion Polymerization of Styrene for the Synthesis of Polymer Nanoparticles

Summary. Suspensions of polymer nanoparticles in water (latices) with average particle diameters between 20 and 80 nm were synthesized by batch emulsion polymerization of styrene using sodium dodecyl sulphate (SDS) as surfactant and potassium persulphate (KPS) as initiator. The influence of surfactant concentration, initiator concentration, monomer concentration, and reaction temperature on the final average particle diameters and size distributions of the latices were studied. The number of particles generated was proportional to the 0.56 power of the emulsifier concentration and to the 0.37 power of the initiator concentration in the whole concentration range which was observed. Furthermore, the final number of particles was dependant on the reaction temperature to the 2.06 power. With these correlations the average particle number as well as the average particle size could be estimated, and the results were in good agreement (±6%) with the experimental values. A reduction of the monomer/water ratio from 1:5 to 1:20 yielded smaller particle diameters, while leaving the particle number unaffected. The lower particle size limits for monomer ratios of 1:10 and 1:15 were estimated with diameters of about 18 and 16 nm.     

表面活性剂对PVDF-SiO_2超滤膜的性能与结构的影响

在PVDF-SiO_2共混膜中添加不同种类的表面活性剂以及两种复配的表面活性剂,通过相转化法制备了一系列的改性膜。实验通过测定未改性膜及改性膜的纯水通量、牛血清白蛋白的截留率、接触角大小、拉伸强度来表征表面活性剂对膜性能的影响,同时通过测试改性膜的通量恢复率来表征膜的抗污染能力。采用扫描电镜(SEM)、X射线衍射(XRD)及热分析(DSC)对膜的微观形貌和晶体结构进行了表征。结果表明,添加单一表面活性剂及复配表面活性剂均可使膜的渗透性能提高,能够改善膜的机械性能、亲水性,对膜的结晶度没有明显的影响,微观结构观察得到改性膜呈现出优化的表面及断面结构,微孔数目变多,孔间的连通性趋好,纳米颗粒在表面分散的更加均匀,改性膜的抗污染性能得到改善。     

Determination of fluorinated surfactants and their metabolites in sewage sludge samples by liquid chromatography with mass spectrometry and tandem mass spectrometry after pressurised liquid extraction and separation on fluorine-modified reversed-phase sorbents

An analytical method was elaborated for simultaneous extraction and determination of fluorinated anionic and non-ionic surfactants in sewage sludge. Surfactant compounds were determined by liquid chromatography-mass spectrometry (LC-MS) after Soxhlet extraction, hot steam extraction and pressurised liquid extraction (PLE) using spiked sludge samples. PLE in a multiple-step procedure consisting of sequential use of ethyl acetate-dimethylformamide and methanol-phosphoric acid resulted in the most efficient extraction procedure. Quantitative analyses of the fluorinated anionic perfluorooctanesulfonate (PFOS) and the partly fluorinated non-ionic alkylpolyglycol ether (FAEO) surfactants were performed by selected ion monitoring LC-MS. Electrospray ionisation or atmospheric pressure chemical ionisation in negative or positive mode was performed. Recoveries between 105 and 120% could be reached. No PFOS and non-ionic FAEO surfactants in concentrations higher than 6 or 10 mg kg(-1) dry matter were observed in real environmental samples. Therefore aerobic and anaerobic biodegradation was performed to investigate the fate of fluorinated surfactants reaching wastewaters. Biological wastewater treatment in laboratory scale under aerobic or anaerobic conditions led to an elimination by biodegradation.     

Morphological evolution and visible light-induced degradation of Rhodamine 6G by nanocrystalline bismuth tungstate prepared using a template-based approach

The cleaning of water contaminated with organic dyes is a crucial problem nowadays. The search for good catalysts is intense, and bismuth tungstates have attracted a lot of attention because of their catalytic properties which are related to their crystal structure and morphology. In this study, we show that Bi₂WO₆ (BWO) crystals synthesized by the surfactant-assisted hydrothermal method create a different morphology than non-assisted crystals. With the assistance of the PVP surfactant, even the BWO crystalline structure could change, crystallizing into a high-symmetry metastable phase. These changes in morphology imply a decrease in BWO catalytic activity, which shows that insightful control of BWO synthesis is necessary to improve the BWO properties.     

Multicanonical Monte Carlo simulations on intramolecular micelle formation in copolymers

The formation of intramolecular micelles in copolymers with periodic sequence, where hydrophobic units (stickers) are periodically placed along the chain, is studied by using multicanonical Monte Carlo computer simulations for an off-lattice bead-rod model in three dimensions. With decreasing the temperature, a transition from random-coil conformations to micelles occurs and flower-type micelles are formed via the transition. The number of stickers forming a micelle core is limited by the excluded-volume effect of loop chains around micelle cores. By this effect, two intramolecular micelles are formed for long polymer chains with 60 bonds via the coil-to-micelle transition. By further decreasing the temperature, we find that another transition, i.e., a micelle-to-micelle transition, takes place. At this transition point, the two intramolecular micelles merge into one micelle. Furthermore, we extend the multicanonical MC method to study elastic properties of single polymer chains with strong attractive interactions under external force fields, and study how the intramolecular micellization affects the elastic property of single polymer chains.     

Analytical applications of organized assemblies for on-line spectrometric determinations: present and future

An amphiphile (surfactant) spread on water can lead to the formation of different aggregates: vesicles, miscelles, emulsions or microemulsions; depending on its concentration; its molecular structure and/or the experimental conditions. Such aggregates, (a) may concentrate products, reactants or analytes and so improve the analytical sensitivity and (b) may solubilize such substances and so favorably change the analytical selectivity. Bilayer membrane vesicles for instance, apart from their wide applications in cosmetic and pharmaceutical industries, have a great analytical potential due to their ability to (i) reversibly sequester metal ions avoiding matrix interference and (ii) improve cold vapor (Hg and Cd) and hydride (As, Se, Pb) chemical generation. Micellar solutions have also found wide applications in different areas of analytical chemistry, showing their capacity to concentrate and separate a significant variety of analytes. Among the numerous micelle-based separation techniques, cloud point extraction offers an excellent enrichment factor for metal ions, allowing their quantification at microgram/litre levels. Also agitating a mixture of water, oil and one or more surfactants under controlled experimental conditions, a cloudy mixture (emulsion) or a transparent solution (microemulsion) can be formed. Adequate formulation is necessary in order to obtain a stable organized media. To fulfill this requirement, a major effort is necessary in order to shorten the gap between the current knowledge on this topic and the promising field of applications that await development. Recent publications show that self-assembly structures from highly viscous samples can be accomplished on-line with the advantages of drastically reducing the time of analysis and assuring the absolute control over the stability of the aggregate. Flow systems allow effective mixing of samples with added surfactant and provide continuous pumping of the resulting mixture to sensitive detectors for the on-line determination of different analytes in complex samples.     

An experimental study of a turbulent shear layer at a clean and contaminated free-surface

An experimental study was performed to measure the flow properties of a vertically-orientated shear layer in the vicinity of a free-surface. The effect of surface contamination on the near surface flow field was also determined. Digital Particle Image Velocimetry was used to measure instantaneous and averaged velocity, vorticity, and Reynolds stresses. Results show that the presence of surfactants can cause directional shifts of the shear layer, as well as an overall damping of the turbulence in the vicinity of the free-surface, except in the vicinity of a Reynolds ridge where an increase in Reynolds stress was observed.     

Synergistic effects in mixed wormlike micelles of dimeric and single-chain cationic surfactants at high ionic strength

The mixed micellization between the cationic gemini surfactant [ C₁₂H₂₅( CH₃)₂N⁺( C₂H₄) N⁺( CH₃)₂ C₁₂H₂₅•2Br^-] and the cationic cetyltrimethylammonium bromide (CTAB) in 150 mM KBr solutions has been investigated. The variation of the cmc of the mixtures, measured by surface tension experiments, with composition revealed synergism in micelle formation. T-Jump and light scattering experiments performed in the vicinity of the crossover volume fraction showed the existence of two micellar populations, possibly linear and toroidal micelles. Rheological and dynamic light scattering experiments allowed to fully characterize the linear viscoelasticity of the mixtures. These measurements revealed synergistic gains in viscoelastic properties with a maximum of the stress-relaxation time around the equimolar composition. These effects are ascribed to a progressive intermicellar crosslinking resulting from a continuous increase of the end-cap energy with the 12-2-12 content in the mixture. Received: 18 November 2002 / Accepted: 8 April 2003 / Published online: 27 May 2003 RID="a" ID="a"e-mail: candau@fresnel.u-strasbg.fr     

Study on the lifetime and attenuation properties of microbubbles coated with carboxylic acid salts

Four kinds of surfactants, sodium laurate, sodium myristate, sodium palmitate and sodium oleate were used to study the effects of surfactant coatings on the lifetime and attenuation of microbubbles. The changes in the size distribution of microbubbles prepared with these surfactants in saline were measured with a Coulter Multisizer (Coulter Electronics Ltd., Luton, UK). Frequency characteristics of ultrasonic attenuation of the microbubble suspensions were measured between 400 kHz and 6 MHz. From the changes in attenuation in the microbubble suspensions over time, it was found that the lifetime of microbubbles in a suspension also depends on the frequency of the irradiating ultrasound. The effect of surfactants on the frequency characteristics of attenuation was also studied, and characteristics of the surfactant coating, including shell elasticity and shell friction parameters were calculated from the measurement results. Microbubbles produced with sodium palmitate had the longest lifetime and the smallest average size. The shell had very little effect on the ultrasonic properties of microbubbles produced with sodium palmitate, suggesting that the sodium palmitate microbubbles behaved ultrasonically as free microbubbles.