Polymerisation of styrene in microemulsion with catanionic surfactant mixtures

The use of aqueous catanionic surfactant mixtures in the oil-in-water (o/w) microemulsion polymerisation of styrene is reported. Catanionic surfactant mixtures of dodecyltrimethylammonium bromide 1 and sodium dodecylsulfate 3, or decanediyl-1,10-bis(dimethyldodecylammonium bromide) 2, a gemini surfactant, and the anionic surfactant 3 were used. Phase behaviour and polymerisation properties of the microemulsions were studied as a function of the total surfactant concentration and the cationic/anionic surfactant ratio. Single-phase o/w microemulsions were only formed if either the cationic or anionic surfactant were present in large excess. Upon -irradiation, polymer nanoparticles were obtained. Using dynamic light scattering, the particle radii were determined to be 10 to 20 nm, the size depending on the total surfactant concentration, the cationic/anionic surfactant ratio and the surfactant/styrene ratio. Size exclusion chromatography indicated molecular weights of polystyrene of between 3×10⁵ and 1.4×10⁶ Daltons. Catanionic 1/3 and 2/3 mixtures differ in their styrene solubilizations. In a 1- or 3-rich system, the solubilization efficiency can be improved by increasing the concentration of the oppositely charged minor surfactant component, while in a 2-rich system the addition of 3 only diminishes the efficiency. Possible reasons for the different behaviours are discussed.     

Formulation ofα-linolenic acid microemulsion free of co-surfactant

<正>A novel class ofα-linolenic acid-in-water microemulsion free of co-surfactant was investigated as potential food delivery systems.Rough demarcation within the transparent region was deduced from the results of conductivity and polarizing optical microscopy.The microemulsion mean hydrodynamic diameter and characterization were determined by dynamic light scattering and negative-staining TEM.The location of ALA molecules in the microemulsion formulations was determined by ~1H NMR spectroscopy.     

Preparation of polyaniline-metal composite nanospheres by in situ microemulsion polymerization

Nanosized metal and polyaniline (PANi) composite spheres have been prepared via the polymerization of aniline using PdCl₂ or HAuCl₄ as the oxidant in a microemulsion system. The oxidization of aniline and the reduction of metal ion happened together during the reaction, yielding PANi and elemental metal simultaneously. The results of FTIR spectra suggested that the oxidation degree of PANi was affected by the initial ratio of metal ions to monomer in the microemulsion system. The PANi–metal nanospheres were characterized using X-ray photoelectron spectroscopy and the conductivity of the composite nanospheres was measured by conventional four-probe method. Scanning and transmission electron microscopy were used to show the morphology of the composites.     

Multiobjective optimization strategy based on desirability functions used for the microemulsion liquid chromatographic separation and quantification of norfloxacin and tinidazole in plasma and formulations

The aim of the present study was to optimize a microemulsion liquid chromatography method for the simultaneous determination of norfloxacin and tinidazole binary mixture using a chemometric protocol. Optimization experiments were conducted through a process of screening and optimization. A 2^7‐4 fractional factorial design was used as screening design. While the location of optimum conditions was established by applying Derringer's desirability function. The optimal mobile phase composition was predicted to be: 3.5% w/v SDS, 10.03% v/v 1‐propanol, 0.5% v/v 1‐octanol, and 0.3% triethylamine in 0.02 M phosphoric acid at pH 6.5. The mobile phase was delivered isocratically at a flow rate of 1 mL/min with UV detection at 290 nm. Tinidazole and norfloxacin were eluted with retention times of 1.8 and 5.8 min, respectively. The calibration plots displayed good linear relationships in the concentration ranges of 0.5–50 and 0.75–75 μg/mL for norfloxacin and tinidazole, respectively. The method was successfully applied for determination of both drugs in pharmaceutical dosage forms and real human plasma. Where the accuracy was proved by the low values of % error and high values of recovery, also the relative standard deviation for the results did not exceed 1.5%, proving the precision of the method.     

Microstructure of microemulsion modified with ionic liquids in microemulsion electrokinetic chromatography and analysis of seven corticosteroids

In this work, the influences of ionic liquid (IL) as a modifier on microemulsion microstructure and separation performance in MEEKC were investigated. Experimental results showed that synergetic effect between IL 1‐butyl‐3‐methylimidazolium tetrafluoro‐borate (BmimBF₄) and surfactant SDS gave a decreased CMC. With increment of IL in microemulsion, negative ζ potential of the microdroplets reduced gradually. The influence of IL on the dimensions of microdroplet was complicated. At BmimBF₄ less than 8 mM, IL made microemulsion droplet smaller in size. While at BmimBF₄ more than 10 mM, the size increased and reached to a maximum value at 12 mM, where the microdroplets were larger than that without IL. After that, the micreodroplet size decreased again. Relative fluorescence intensity of the first vibration band of pyrene to the third one (I₁/I₃) enhanced as IL was added to microemulsion, which indicated that this addition increased environmental polarity in the inner core of microdroplets. Prednisone, hydrocortisone, prednisolone, hydrocortisone acetate, cortisone acetate, prednisolone acetate, and triamcinolone acetonide were analyzed with MEEKC modified with IL to evaluate the separation performance. Cortisone acetate and prednisolone acetate could not be separated at all in typical microemulsion. The seven analytes could be separated by the addition of 10 mM BmimBF₄ into the microemulsion system. The method has been used for analysis of corticosteroids in cosmetic samples with simple extraction; the recoveries for seven analytes were between 86 and 114%. This method provides accuracy, reproducibility, pretreatment simplicity, and could be applied to the quality control of cosmetics.     

Determination of manganese in diesel,gasoline and naphtha by graphite furnace atomic absorption spectrometry using microemulsion medium for sample stabilization

The determination of Mn in diesel, gasoline and naphtha samples at µg L^− 1 level by graphite furnace atomic absorption spectrometry, after sample stabilization in a three-component medium (microemulsion) was investigated. Microemulsions were prepared by mixing appropriate volumes of sample, propan-1-ol and nitric acid aqueous solution, and a stable system was immediately and spontaneously formed. After multivariate optimization by central composite design the optimum microemulsion composition as well as the temperature program was defined. In this way, calibration using aqueous analytical solution was possible, since the same sensitivity was observed in the optimized microemulsion media and 0.2% v/v HNO₃. The use of modifier was not necessary. Recoveries at the 3 µg L^− 1 level using both inorganic and organic Mn standards spiked solutions ranged from 98 to 107% and the limits of detection were 0.6, 0.5 and 0.3 µg L^− 1 in the original diesel, gasoline and naphtha samples, respectively. The Mn characteristic mass 3.4 pg. Typical relative standard deviation (n = 5) of 8, 6 and 7% were found for the samples prepared as microemulsions at concentration levels of 1.3, 0.8, and 1.5 µg L^− 1, respectively. The total determination cycle lasted 4 min for diesel and 3 min for gasoline and naphtha, equivalent to a sample throughput of 7 h^− 1 for duplicate determinations in diesel and 10 h^− 1 for duplicate determinations in gasoline and naphtha. Accuracy was also assessed by using other method of analysis (ASTM D 3831-90). No statistically significant differences were found between the results obtained with the proposed method and the reference method in the analysis of real samples.     

Direct determination of arsenic and antimony in naphtha by electrothermal atomic absorption spectrometry with microemulsion sample introduction and iridium permanent modifier

This paper reports the determination of arsenic and antimony in naphtha by employing electrothermal atomic absorption spectrometry (ETAAS) as the analytical technique. In order to promote the direct determination of the analytes in the very volatile naphtha, the formation of a microemulsion with different surfactants (Triton X-100 and Brij-35) and different chemical modification strategies were tested. The results indicated that Triton X-100 is the best emulsification agent for naphtha in both As and Sb determination when it is employed at a concentration of 1% w/v in the microemulsion. Under these conditions, the microemulsion was stabile for at least 2 h. By using Brij-35 it was possible to achieve good stability only in the first 15 min. Among all chemical modification approaches investigated (Ir permanent modifier, W-Ir permanent modifier, and Pd modifier), the Ir permanent modifier provided better sensitivity for both analytes and allowed a higher pyrolysis temperature, which decreased the background signals at lower levels. Under the best conditions established in this work, an RSD of 4.6% (20 g L^–1) and a detection limit of 2.7 g L^–1 were observed for arsenic. For antimony, an RSD of 4.0% (20 g L^–1) and a detection limit of 2.5 g L^–1 were obtained. The accuracy of the procedure was assessed by analyzing spiked samples of naphtha from different origins.     

Chiral separations in microemulsion electrokinetic chromatography. Use of micelle polymers and microemulsion polymers

In this study, microemulsions of the chiral surfactant polysodium N-undecenoyl-D-valinate (poly-D-SUV) was utilized for enantiomeric separation by investigating two approaches using polymeric chiral surfactant in microemulsion electrokinetic chromatography (MEEKC). In the first approach, poly-D-SUV was used as an emulsifier surfactant along with 1-butanol and n-heptane. Enantioseparation of anionic or partially anionic binaphthyl derivatives, anionic barbiturates, and cationic paveroline derivatives were achieved by varying the mass fraction of 1-butanol, n-heptane and poly-D-SUV. For anionic or partially anionic analytes, relatively lower mass fractions of n-heptane, and poly-D-SUV were found to give optimum chiral separations as compared to that for cationic solutes. In the second approach, the chiral microemulsion polymer was prepared by polymerizing mixtures of 3.50% (w/w) of sodium N-undecenoyl-D-valinate (D-SUV) and 0.82% (w/w) of n-heptane (core phase) at varying concentration of 1-butanol. After polymerization, the n-heptane and 1-butanol were removed to yield solvent free microemulsion polymers (MPs) which were then utilized for the separation of anionic binaphthyl derivatives and anionic barbiturates. When MPs of D-SUV were utilized for chiral separation, 1.00% (w/w) 1-butanol and 3.50% (w/w) 1-butanol was optimum for enantioseparation of (+/-)-BNP and (+/-)-BOH, respectively. On the other hand, for anionic (+/-)-barbiturates very low concentration of butanol (0.25%, w/w) provided optimum resolution. Compared with micellar electrokinetic chromatography (MEKC), the use of micelle polymers or microemulsion polymers in MEEKC showed dramatic enhancement for resolution of (+/-)-BNP, while this enhancement was less dramatic for other binaphthyls [(+/-)-BOH, (+/-)-BNA] as well as for (+/-)-barbiturates and (+/-)-paveroline derivatives. However, higher separation efficiency of the enantiomers was always observed with MEEKC than in MEKC.     

Desirability-based optimization and its sensitivity analysis for the perindopril and its impurities analysis in a microemulsion LC system

In the current paper the application of multiobjective optimization (MOOP) technique, via Derringer's desirability function, to a microemulsion liquid chromatographic (MELC) method is described. Chromatographic separation of perindopril tert-butylamine and its four impurities was selected as the case study. Central composite design (CCD) with fractional factorial design, ± 0.5 α star design and four replications in central point was applied for a response surface study, in order to examine in depth the effects of the most important factors. As factors that influence the system mostly (i) content of ethyl acetate and (ii) butyl acetate in composite internal phase, (iii) content of sodium dodecyl sulfate (surfactant) and (iv) n-butanol (co-surfactant), as well as (v) pH of the mobile phase were selected. Retention factor of (a) perindoprilat and (b) impurity Y 31 and (c) resolution factor for impurities Y 32 and 33 were chosen for simultaneous optimization. By adjustment of the importance coefficients and weights, according to defined objectives, the optimal mobile phase composition was predicted to be: 0.24% w/v butyl acetate, 0.3% w/v ethyl acetate, 2% w/v SDS, 7.75% w/v n-butanol and pH of the mobile phase 3.7. The sensitivity analysis of desirability function for these optimal conditions was conducted for the first time in LC separations, by applying a sensitivity procedure. The performed sensitivity analysis confirmed that the higher overall desirability does not necessarily mean a better solution. The accuracy of prediction might be affected if the optimal levels of input variables, achieved from several design points, end up with equal settings and different corresponding overall desirability. In our study this was not the issue, which confirmed the adequacy of predicted optimum.     

On the copolymerization of acrylates in the modified microemulsion process

Copolymerization of methyl methacrylate, methyl acrylate, butyl methacrylate, and butyl acrylate in turn was performed in the modified microemulsion polymerization process, i.e., continuous addition of monomer to a preemulsified system. It was found that the particle size of the copolymer microlatex did not change distinctly with the monomer composition. The estimation of emulsifier coverage on the microlatex particles indicated that the process switched from a traditional microemulsion to a normal seeded emulsion polymerization very soon after monomer dropping began. Therefore, a longer dropping time is needed to produce a microlatex with narrow dispersed particle size. Besides, in the modified microemulsion polymerization less emulsifier is needed to produce a stable microlatex. This behavior is related to the mechanism of normal seeded emulsion polymerization during monomer dropping.     

微乳液增敏测定药物中微量铋

研究了多种胶束及微乳液对水杨基荧光酮光度法测定铋的增敏作用,并选择增敏作用最强的微乳液作为铋测定的增敏试剂,确定最佳条件。结果表明,在微乳液(OP 正丁醇正庚烷水)存在下,铋与水杨基荧光酮在H2SO4介质中可以形成紫红色配合物,配合物的最大吸收峰位于516nm波长处,表观摩尔吸光系数为ε=1.17×105L·mol-1·cm-1。铋量在0～1 2μg mL范围内符合比尔定律。本法可用于胃药中铋的测定。     

Separation and determination of flavonoids using microemulsion EKC with electrochemical detection

A selective and sensitive method of microemulsion EKC (MEEKC) with electrochemical detection (ED) was developed for separation and determination of 14 flavonoids. In order to obtain the better stability for the studied flavonoids, oil (ethyl acetate) with low interfacial surface tension was employed as organic solvent. A running buffer composed of 0.9% (w/v, 30 mM) SDS, 0.9% (w/v, 21 mM) sodium cholate (SC), 0.9% (w/v, 121 mM) butan-1-ol, 0.6% (w/v, 68 mM) ethyl acetate, and 98.2% v/v 10 mM Na(2)B(4)O(7)-20 mM H(3)BO(3) buffer (pH 7.5) was applied for the separation of flavonoids. Under the optimum conditions, the relationship between peak currents and analyte concentrations was linear over about 1.3 and 1.7 orders of magnitude with detection limits (defined as S/N = 3) ranging from 0.02 to 0.5 microg/mL for all analytes. This method was applied for the determination of flavonoids in real samples with simple extraction procedures, and the assay results were satisfactory.     

Dark singlet oxygenation of organic substrates in single-phase and multiphase microemulsion systems

The disproportionation of hydrogen peroxide catalyzed by molybdate anions provides an effective non-photochemical source of singlet oxygen ¹O₂, (¹Δ_g). Microemulsions are the preferred media to carry out ‘dark’ singlet oxygenation of labile and hydrophobic substrates. Single-phase and multiphase microemulsion systems have been developed and improved for the last decade and their respective advantages and limitations are shortly reviewed and discussed.     

微乳液光度法快速测定钢中的磷

在非离子型微乳液(OP/n-C5H11 OH/n-C7H16/H2O)存在下,乙基紫与磷钼钒杂多酸在0.7~1.0 mol/,L H2SO4介质中形成吸附型离子缔合物,该缔合物的组成为磷钼钒杂多酸:乙基紫=1:2,最大吸收波长为612 nm,表观摩尔吸光系数ε=1.58×105L·mol-1·cm-1,磷质量浓度在0....     

Microstructure of microemulsion in MEEKC

The influences of the composition of microemulsion on the microstructure including dimensions and ζ potentials of microdroplets were measured in details. The average dynamic dimension of microdroplets was measured by dynamic laser light scattering, and ζ potential was determined to characterize average surface charge density of microdroplets. The experiment results showed that increase of the amount of surfactant resulted in decrease of microdroplet size but almost invariant ζ potential, which would enlarge migration time of the microdroplet in MEEKC. With increment of cosurfactant concentration, the microdroplet size had an increasing trend, whereas the ζ potential decreased. Thus, observed migration velocity of microdroplets increased, which made the separation window in MEEKC shortened. Neither dimension nor ζ potential of microdroplets changed by varying both the type and the amount of the oil phase. Adding organic solvent as modifier to microemulsion did not change the microdroplet size, but lowered ζ potential. The migration time of microdroplet still became larger, since EOF slowed down owing to organic solvent in capillary. So, besides increment of surfactant concentration, organic additive could also enlarge the separation window. Increase of cosurfactant concentration was beneficial for separation efficiency thanks to the looser structure of swollen microdroplet, and the peak sharpening might compensate for the resolution and peak capacity owing to a narrow separation window. Except the oil phase, tuning the composition of microemulsion would change the microstructure, eventually could be exploited to optimize the resolution and save analysis time in MEEKC.     

Synthesis and characterization of Eu-doped hydroxyapatite through a microwave assisted microemulsion process

Europium doped hydroxyapatite (Eu:HAp) nanosized particles with multiform morphologies have been successfully prepared via a simple microemulsion-mediated process assisted with microwave heating. The physicochemical properties of the samples were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) spectra, and the kinetic decays, respectively. The results reveal that the obtained Eu:HAp particles are well assigned to the hexagonal lattice structure of the hydroxyapatite phase. Additionally, it is found that samples exhibit uniform morphologies which can be controlled by altering the pH values. Furthermore, the samples show the characteristic ⁵D₀–⁷F_1–4 emission lines of Eu³⁺ excited by UV radiation.     

Retention modelling in liquid chromatographic separation of simvastatin and six impurities using a microemulsion as eluent

A novel and unique approach was used for retention modelling in the separation of simvastatin and six impurities by liquid chromatographic using a microemulsion as mobile phase. A microemulsion is a modification of a micellar system where a lipophilic organic solvent is dissolved in the micelles; for that reason, microemulsions are usually treated as solvent-modified micellar solutions. When microemulsions are used as eluents in HPLC separations, solutes partition between the charged oil droplets and the aqueous buffer phase. The complexity of the composition of the microemulsion permits extensive manipulations to be made during method development in order to achieve acceptable resolution of such a complex mixture of substances. In order to avoid a laborious "trial and error" procedure, a 2(3) full factorial design was applied for choosing an optimal microemulsion composition to obtain good separation in a reasonable run time. Organic solvent, sodium dodecyl sulphate, and n-butanol content were varied within defined experimental domain. Optimal conditions for the separation of simvastatin and its six impurities were obtained using an X Terra 50 x 4.6 mm, 3.5 microm particle size column at 30 degrees C. The mobile phase consisted of 0.9% w/w of diisopropyl ether, 2.2% w/w of sodium dodecylsulphate (SDS), 7.0% w/w of co-surfactant such as n-butanol, and 89.9% w/w of aqueous 25 mM disodium phosphate pH 7.0.     

Preparation and morphology of SiO2/PMMA nanohybrids by microemulsion polymerization

Polymethylmethacrylate/SiO2 nanocomposite particles were prepared through microemulsion polymerization by using the silica particles coated with 3-(trimethoxysilyl) propyl methacrylate (MSMA) in both acidic and alkaline conditions. Core-shell and other interesting morphology nanocomposite particles were obtained depending on the pH of the microemulsion, the amount of silanol, and the coupling agent concentration employed. Then, by combining a modified microemulsion polymerization process, i.e., an additional monomer-adding process, the solid contents of the polymer/inorganic nanocomposite microemulsion could greatly increase. Thus, by adjusting these parameters and polymerization process, it was possible to control the morphology and size of the nanocomposites.