Fluorescence Spectroscopy Study of Polyoxyethylene Surfactant Micellar Systems

The systems investigated by fluorescence spectroscopy and atomic force microscopy were water/ethoxylated mono, di-glyceride/oil + ethanol. The oils were R (+)-limonene and isopropylmyristate. The mixing ratio (w/w) of ethanol/oil equals unity. The fluorescent probes auramine-O and 8-anilino-1-naphthalenesulfonic acid were used to determine the minimum ω′ value for the transition of reverse micelles to microemulsions in the systems based on the two oils, as well as at different surfactant contents. The fluorescence quenching of Safranine-T (3,6-diamino-2,7-dimethyl-5 phenyl phenazinium chloride) by the inorganic ions Fe²⁺, Fe³⁺ and Cu²⁺ was studied in reverse micelles and microemulsions. The Stern–Volmer quenching constants at different water/surfactant molar ratios (ω values) were calculated from the data of the quenching process. Atomic force microscopy was used to image the systems based on the two oils for different water to surfactant molar ratios below and above the minimum ω′ value.     

Endogenous growth of the population of reverse micelles

The coupling reaction between cetylbromide (CB) and trimethylamine (TMA) to yield the surfactant cetyltrimethylammonium bromide (CTAB) is studied in the system chloroform/isooctane (2/1,v/v)/water in which CTAB forms reverse micelles. This system affords an endogenous micelle population growth, i.e., an increase of the concentration of the micelles due to appearance of the surfactant in situ. The reaction is studied in the presence of preexisting CTAB reverse micelles. The rate of CTAB formation is measured by NMR spectroscopy, and the endogenous micelle population growth is directly monitored by time-resolved fluorescence quenching analysis. Under our experimental conditions, a 100% yield of the chemical reaction brings about a fourfold increase in the population of the reverse micelles. Since the water concentration is constant during chemical reaction, the newly formed water pools are formed at the expense of the initial ones, which brings about a decrease of the average water pool radius during micellar growth. The implication of the endogenous micelle population growth as a model for biological systems is briefly discussed.     

Structural properties of palladium nanoparticles embedded in inverse microemulsions

Pd nanoparticles were synthesized by reduction of palladium acetate by ethanol in systems containing tetrahydrofuran (THF) as dispersion medium and tetradodecylammonium bromide (TDABr) surfactant as stabilizer. The polar phase (ethanol) acts at the same time as reducing agent. THF/TDABr/H₂O inverse microemulsions containing micelles of various sizes were also prepared, and the structure of complex liquids was studied by density measurements. Sols containing nanosize Pd⁰ particles were synthesized within the water droplets of this micellar system. The stabilized Pd⁰/surfactant system was characterized by density measurements, absorption spectroscopy, and transmission electron microscopy. The stabilizing surfactant layer adsorbed on the liquid/liquid interface and on the surface of the nanoparticles (i.e., the liquid/solid interface) significantly reduced the excess volume for the palladium nanodispersion in organic solvent. Received: 17 July 2000 Accepted: 5 October 2000     

Solubilized states of water and formation of reversed micelles in polyoxyethylated nonylphenyl ethers in cyclohexane media

The limiting amounts of solubilization of water in the concentration range 0–200 mmol kg^–1 polyoxyethylene (6 and 10) nonylphenyl ethers (NP-6 and NP-10)/cyclohexane solutions were measured by the Karl-Fischer method at 25°C. Utilizing NMR, ESR, and near infrared spectroscopic techniques, the states of water in the solubilization region obtained were examined as a function of the molar ratio of water to surfactants at various surfactant concentrations. In NP-6 system, three solubilized states of water, i.e., water interacted directly with the oxyethylene moiety of surfactant, bound water next to the hydrated oxyethylene moiety, and bulk-like water were built up. However, in NP-10 system only directly interacted water was present. It was found that the directly interacted water is distributed between monomeric surfactants and reversed micelles, and others are distributed to swollen micelles and W/O microemulsions. In addition, the minimum amounts of water required to form reversed and swollen micelles were calculated.     

Growth of silica nanoparticles in methylmethacrylate-based water-in-oil microemulsions

The mechanism of silica particle formation in monomer microemulsions is studied using dynamic light scattering (DLS), atomic force microscopy, small-angle X-ray scattering (SAXS), and conductivity measurements. The hydrolysis of tetraethylorthosilicate (TEOS) in methylmethacrylate (MMA) microemulsions (MMA = methylmethacrylate) is compared with the formation of SiO₂ particles in heptane microemulsions. Stable microemulsions without cosurfactant were found for MMA, the nonionic surfactant Marlophen NP10, and aqueous ammonia (0.75 wt%). In the one-phase region of the ternary phase diagram, the water/surfactant ratio (R _w) could be varied from 6 to 18. The DLS and SAXS measurements show that reverse micelles form in these water-in-oil (w/o) microemulsions. The minimum water-to-surfactant molar ratio required for micelle formation was determined. Particle formation is achieved from the base-catalyzed hydrolysis of TEOS. According to atomic force microscopy measurements of particles isolated from the emulsion, the particle size can be effectively tailored in between 20 and 60 nm by varying R _w from 2–6 in heptane w/o microemulsions. For MMA-based microemulsions, the particle diameter ranges from 25 to 50 nm, but the polydispersity is higher. Tailoring of the particle size is not achieved with R _w, but adjusting the particle growth period produces particles between 10 and 70 nm.     

Properties of microemulsions with sugar surfactants and peppermint oil

In this study, we report on the properties of water + propylene glycol/sugar surfactant/peppermint oil + ethanol. The sugar surfactants were sucrose monolaurate and sucrose dilaurate. The mixing ratios (w/w) of water/propylene glycol and that of ethanol/oil equal 2 and 1, respectively. U-type microemulsions were observed in the sucrose monolaurate while S-type microemulsions were observed in the dilaurate-based systems. Temperature-insensitive microemulsions were formulated using the two surfactants. Water volume fraction percolation thresholds were determined by the study of electrical conductivity and dynamic viscosity. The structural parameters that include the periodicity and the correlation length were estimated using small angle X-ray scattering. The periodicity increases linearly with the increase in the water content whereas the correlation length increases with the increase in the water volume fraction to a certain value then decreases. The diffusion properties investigated by nuclear magnetic resonance confirm a progressive transformation of the microemulsions from water-in-oil to bicontinuous and inversion to oil-in-water upon dilution with water. The hydrodynamic radius of diluted microemulsions measured by dynamic light scattering increases with the increase in temperature. The area per polar head group decreases with the increase in temperature. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Small-angle neutron scattering and theoretical investigation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) stabilized oil-in-water microemulsions

The aim of this study is to determine the effects of oil solutes and alcohol cosolvents on the structure of oil-in-water microemulsions stabilized by poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers. The systems investigated involved the solubilization of 1,3,5-trimethylbenzene or 1,2-dichlorobenzene by P123 (EO(20)-PO(70)-EO(20)) pluronic surfactant micelles in water and water + ethanol solvents. The structures of these swollen micelles were determined by small-angle neutron scattering (SANS). A thermodynamic model was employed to interpret the characterization data. The results of the thermodynamic model for micellization agreed well with the SANS data from samples of micelles swollen by both oils. The model predicted the size of the micelles within 5% accuracy using only one fitting parameter, the micelle polydispersity. Ethanol had significantly different effects on the polymer micelles that contained solubilized oil compared to pure polymer micelles. For pure polymer micelles, the addition of ethanol increased the solubility of the polymer and, therefore, decreased the total volume fraction of micelles, while for polymer-oil aggregates, ethanol tended to have a positive effect on the volume fraction of micelles. SANS results showed that the greatest divergence from pure aqueous solvent results occurred at oil concentrations above the microemulsion stability limit.     

Interaction between biosurfactant surfactin and cationic surfactant cetyl trimethyl ammonium bromide in mixed micelle

An anionic/cationic mixed surfactant aqueous system of surfactin and cetyl trimethyl ammonium bromide (CTAB) at different molar ratios was studied by surface tension and fluorescence methods (pH 8.0). Various parameters that included critical micelle concentration (cmc), micellar composition (X ₁), and interaction parameter (β ^m) as well as thermodynamic properties of mixed micelles were determined. The β ^m was found to be negative and the mixed system was found to have much lower cmc than pure surfactant systems. There exits synergism between anionic surfactin and cationic CTAB surfactants. The degree of participation of surfactin in the formation of mixed micelle changes with mixing ratio of the two surfactants. The results of aggregation number, fluorescence anisotropy, and viscosity indicate that more packed and larger aggregates were formed from mixed surfactants than unmixed, and the mixed system may be able to form vesicle spontaneously at high molar fraction of surfactin.     

Influence of Confined Water on the Photophysics of Dissolved Solutes in Reverse Micelles

The photophysical parameters of two probes with largely different hydrophobic character, namely, coumarin 1 and coumarin 343, are investigated in sodium bis‐(2‐ethylhexyl)sulfosuccinate (AOT)/hexane/water reverse micelles at various water/AOT molar ratio w₀. Correlation of photophysical parameters such as fluorescence quantum yield, fluorescence lifetime, and emission maxima with w₀ indicate distinctly different trends below and above w₀≈7 for both probes. The variation of the average rotational correlation times obtained from fluorescence anisotropy decays for both probes in reverse micelles further corroborate the above observation. Similar studies were also performed in nonaqueous reverse micelles with acetonitrile as polar solvent. Similar to aqueous reverse micelles, breaks in the photophysical parameters with increasing acetonitrile/AOT molar ratios w′₀ were also observed in these cases, although at a much lower w′₀ value of 3. The present results indicate that around w₀≈7 for aqueous reverse micelles (and around w′₀≈3 for nonaqueous reverse micelles) a distinct change occurs in the probe microenvironment, which is rationalized on the basis of the relative populations of interfacial and core water. We propose that until the ionic head groups and counterions are fully solvated by polar solvents, that is, up to w₀≈7 (or w′₀≈3), the interfacial water population dominates. Above these molar ratios coalescence of excess water molecules with each other to form truncated H‐bonded water clusters leads to a sizable population of core water. This is further substantiated by changes in the IR absorption spectra for the O? D stretching mode of diluted D₂O in reverse micelles with varying w₀. Critical comparison of the present results with relevant literature reports provide clear support for the proposals made on water structure in reverse micelles. The role of relative size of the probe and the reverse micelles for differences in polar solvent to AOT ratios (w₀=7 and w′₀=3) in the observed breaks in the two types of reverse micelles is also discussed.     

Fluorescence in microemulsions and reversed micelles : A Review and New Results

The use of fluorescence to study physicochemical structures of alcohol/surfactant/water systems, microemulsions and reversed micelles is reviewed, and the application of these media in analytical fluorescence spectroscopy is discussed. The sodium dodecylsulfate/1-pentanol/heptane/ water system is studied by using pseudo-ternary diagrams. Wide areas of existence of thermodynamically stable and optically clear phases (Winsor IV and two liquid crystals) were found both in the absence and presence of sodium sulfate (0.2 M). The influence of the composition of media on the fluorescence characteristics of pyrene, benzo [e]pyrene, 2-naphthol and p-amino-benzoic acid is studied.     

Flocculation of anionic surfactant micelles in the presence of hydrocarbons

Adsorptive micellar flocculation (AMF) is a surfactant-based separation process based on the flocculation of micelles of suitable anionic surfactants by Al³⁺. The micelles form large amorphous flocs which can be removed by filtration, which is attractive because soluble pollutants are captured by the floc, thus providing a simple separation method. As the primary aim of AMF is the removal of anionic pollutants from aqueous streams, it is important to investigate the influence of the various substances which may affect it. This article discusses the influence of the presence of insoluble hydrocarbons on the flocculation of micelles of the anionic surfactant dodecyl sulfate by Al³⁺. The ratio between surfactant remaining in solution and total surfactant and the ratio between Al³⁺ and surfactant in the flocculate are determined in systems composed of an aqueous solution containing a constant dodecyl sulfate concentration of 0.05 M and a variable Al³⁺ concentration and an organic phase (decane) with phase volume ratios of decane/water ranging from 0 (no decane) to 0.15. The flocculation is only slightly affected by the presence of decane for decane/solution ratios below 0.05, while the effect (lower flocculated fraction) is more marked above this ratio. Received: 25 October 1999/Accepted: 7 February 2000     

A Sensitive Fluorescence Quenching Method for the Determination of Iron( Ⅱ） with 1,10-Phenanthroline

A sensitive and selective fluorescence quenching method for the determination of Fe²⁺ with 1,10‐phenanthroline was developed. The fluorescence intensity of 1,10‐phenanthroline at λ_ex of 266 run and λ_em of 365 nm was constant in the range of pH 4.0 to 10.0 and decreased linearly upon addition of Fe²⁺ to its solution. This decrease was mainly due to a static quenching effect caused by the formation of a non‐fluorescent complex of Fe²⁺ with 1, 10‐phenanthroline. The total amount of iron was determined by using hydroxylamine hydrochloride to reduce Fe³⁺ to Fe²⁺. The linear range was from 5.0 × 10–⁷ to 2.0 × 10–⁵ mol/L with a detection limit of 2.4 × 10–⁸ mol/L at 3s?. The quenching constant of Fe²⁺ to 1,10‐phenanthroline was calculated to be (5.70 × 0.05) × 10⁴ L/mol at 25 °C. Effects of foreign ions on the determination of Fe²⁺ were investigated. The results of the new method for the determination of iron in tap water and natural water samples were in good agreement with those obtained by graphite atomic absorption spectrometry.     

Surfactant Chain Length Effect on the Structural Parameters of Nonionic Microemulsions

In this study we estimated the structural parameters of (water+propylene glycol)/sucrose esters/(benzaldhyde+ethanol) systems. The weight ratios of water/propylene glycol and that of benzaldhyde/ethanol equal 2 and 1, respectively. The sucrose esters were sucrose laurates (L595, L1695, and SM1200), sucrose myristate (M1695), sucrose palmitate (P1670), sucrose oleate (O1570), and sucrose stearate (S1570). The pseudoternary phase behavior at 37°C was explored to determine the extension of the microemulsion phase regions. A one‐phase microemulsion region extending from the oil rich region to the water rich corner was observed in these systems. It was found that minor changes in the surfactant chain length, structure, and composition suffice to provoke a considerable change in the aggregation number, core radius and interfacial area per surfactant and cosurfactant molecules head groups in the formed microemulsions. The interfacial area per surfactant head group decreases with the increase in the surfactant chain length. For a sucrose ester with a given chain length the interfacial area per surfactant head group decreases with the increase in the surfactant monoester content. The interfacial area per surfactant head group increases with the increase in the surfactant concentration and the water core volume in the formulated microemulsions.     

Physicochemical investigation of the solubilization of ytterbium nitrate in AOT reverse micelles and liquid crystals

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 ¹H NMR spectroscopies, some information on the state of Yb(NO₃)₃ within AOT reverse micelles were acquired, whereas by small angle X-ray scattering (SAXS), it has been ascertained that Yb(NO₃)₃ is quite homogeneously distributed as very small clusters among the reverse micelles. An analysis of SAXS and wide-angle X-ray scattering spectra of Yb(NO₃)₃/AOT composites leads to the hypothesis that, also in these systems, Yb(NO₃)₃ is dispersed in the surfactant matrix as very small clusters.     

The effect of the initial reactant molar ratio and doping with Fe<Superscript>3+</Superscript> on the formation of calcium bilirubinate in water-oil microemulsions

A series of calcium bilirubinate nanoparticles were synthesized in microemulsions consisting of polyoxyethylene octylphenol ether (Triton X-100), n-hexyl alcohol (n-C₆H₁₃OH), cyclohexane (c-C₆H₁₂), and an aqueous solution. The particles were characterized by Fourier transform infrared (FT-IR) spectra, powder X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-AES), transmission electron microscopy (TEM), and zeta potential measurements. The results showed that the initial CaCl₂/Na₂BR molar ratio and the molar ratio of water to surfactant (ω₀) influenced the morphology and microstructure of calcium bilirubinate nanoparticles and the sites of Ca²⁺ coordination to BR²⁻. The composition of synthesized calcium bilirubinate was nonstoichiometric. The stability of calcium bilirubinate nanoparticles dispersed in water changes as the Ca²⁺/BR²⁻ molar ratio and solution pH varied. Dopant Fe²⁺ ions played a certain role in the simulated mineralization of calcium bilirubinate. A possible mechanism of calcium bilirubinate formation in inverse microemulsions is discussed. The text was submitted by the authors in English.     

Water Solubilization in Mixed Nonionic Surfactants Microemulsions

The systems investigated were water/sucrose laurate/ethoxylated mono-di-glyceride/oleic phase. The oleic phase used first was the pure oils R (+)-limonene, isopropylmyristate, and caprylic-capric triglyceride; these oils were then mixed with ethanol at different mixing ratios (w/w). The total area of the one phase microemulsion region is dependent on the mixing ratios (w/w) of the mixed surfactants and that of the ethanol/oil. The largest microemulsion phase area formed with a surfactants mixing ratio (w/w) equals unity. For the systems where the oleic phase was a mixture of oil and ethanol, the total area of the monophasic microemulsion increases with the increase in the ethanol/oil mixing ratio (w/w). The Gibbs free energy of solubilization was estimated. It increases as the mixing ratio (w/w) of ethoxylated mono-di-glyceride/sucrose laurate increases and with the increase in the ethanol/oil mixing ratio (w/w). The Gibbs free energy of solubilization decreases with the increase in the water content in the water-in-oil microemulsions. The values of the Gibbs free energy of solubilization are higher for oil-in-water microemulsions compared to those of the water-in-oil microemulsions.     

Selective Chemosensor of Fe3+ Based on Fluorescence Quenching by 2,2′‐Bisbenzimidazole Derivative in Aqueous Media

2,2′‐Bisbenzimidazole derivative ( L ) was designed as a fluorescent chemosensor for Fe³⁺. This structurally simple chemosensor displays significant fluorescence quenching with increasing concentrations of Fe³⁺. L exhibited high selectivity and antidisturbance for Fe³⁺ among environmentally relevant metal ions in aqueous media. The method of Job's plot indicated the formation of 1:2 complex between L and Fe³⁺, and the possible binding mode of the system was also proposed. In addition, further study demonstrates the detection limit on fluorescence response of the sensor to Fe³⁺ is down to 10^?7 mol·L^?1 range. The binding mode was investigated by fluorescence spectra, ESI‐MS, IR data, ¹H NMR, ¹³C NMR and crystal data.     

A high-efficiency and low-cost AEE polyurethane chemo-sensor for Fe3+ and explosives detection

An aggregation enhanced emission (AEE) polyurethane named STMPU-211 containing 0.13% mole concentration of 4,4′-((1Z,3Z)-1,4-diphenylbuta-1,3-diene-1,4-diyl) dibenzaldehyde (TABDAA) in the soft segments was synthesized and proved to be sensitive to Fe³⁺ and nitroaromatic explosives. The fluorescence of the AEE polyurethane was reduced in the presence of Fe³⁺, and almost quenched when 5000?μM Fe³⁺ was added. Meanwhile, the fluorescence intensity of STMPU-211 solution in DMF/water mixture was decreased when explosives like 2,4,6-trinitrophenol (PA) and 3-nitro-1,2,4-triazol-5-one (NTO) were applied. Especially, the quenching coefficient K_SV value of PA was 5.7?×?10⁶?M^?1, confirming that the polyurethane STMPU-211 could be a highly sensitive sensor for the detection of PA. Therefore, AEE polyurethanes with low concentration of TABDAA have promising applications in biological probe, environment monitoring and antiterrorism fields.     

Formation of water-in-CO(2) microemulsions with non-fluorous surfactant Ls-54 and solubilization of biomacromolecules

The solubility of Ls-54 surfactant in supercritical CO(2) was determined. It was found that the surfactant was highly soluble in SC CO(2) and the water-in-CO(2) microemulsions could be formed, despite it being a non-fluorous and non-siloxane nonionic surfactant. The main reasons for the high solubility and formation of the microemulsions may be that the surfactant has four CO(2)-philic groups (propylene oxide) and five hydrophilic groups (ethylene oxide) and its molecular weight are relatively low. The results of this work provide useful information for designing CO(2)-soluble non-fluorous and non-siloxane surfactants. The phase behavior of the CO(2)/Ls-54/H(2)O system, solvatochromic probe study, and the UV spectrum of lysozyme proved the existence of water domains in the SC CO(2) microemulsions. The method of synchrotron radiation small-angle X-ray scattering was used to obtain the structural information on the Ls-54 based water-in-CO(2) reverse micelles. By using the Guinier plot (ln I(q) versus q (2)) on the data sets in a defined small q range (0.022-0.040 A(-1)), the radii of the reverse micelles were obtained at different pressures and molar ratio of water to surfactant, W(0), which were in the range of 20.4-25.2 A.     

混合反胶束的电导与微结构研究

反胶束是两亲分子在非极性溶剂中形成的一种有序组合体，在医药、化工、采油、胶束催化及酶催化等领域中有重要应用．与胶束溶液相比，人们对反胶束的形成与结构的了解至今仍不充分．特别是对于由混合表面活性剂形成的反胶束的研究几乎无人涉及．本文采用动态光散射、电导及荧光光谱等手段对阴离子表面活性剂AOT与非离子表面活性剂形成的混合反胶束进行了研究，旨在探讨利用表面活性剂的复配来调节和控制反胶束的结构和性能．亚实验部分二异辛基磺化琉璃酸钠（AOT，Sigma公司）；Brij30为含4个氧乙烯基（EO基）的十二碳醇（AcrosOrgani…