Anionic Microemulsions Research Articles

Efficient extraction of phenol from wastewater by ionic micro-emulsion method: Anionic and cationic

Phenolic wastewater is one of the priorities in the field of wastewater treatment, which poses a serious threat to the human health and nature environment. In this paper, cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium oleate (NaOL) microemulsions were utilized to extract phenol from the wastewater. The optimal extraction factors were investigated by exploring the effects of microemulsion composition ratio and extraction conditions on the phenol extraction performance. Furthermore, the enhanced extraction mechanism of phenol by cations microemulsions is illustrated by studying the extraction process of cationic and anionic microemulsions in the extraction of phenol. The optimum components were obtained: surfactant concentration of 0.2 mol·L–1, isoamyl alcohol volume of 30%, internal aqueous phase concentration of CTAB microemulsion of 0.05 mol·L–1, and internal aqueous phase concentration of NaOL microemulsion of 0.09 mol·L–1. The extraction efficiencies were 96.44% and 82.0% when using CTAB and NaOL microemulsions under optimal conditions (water–emulsion ratio of 5, contact time of 9 min, extraction temperature of 298.15 K, and pH of 9), confirming the enhanced extraction of phenol by CTAB cationic microemulsion. It was analyzed that the enhanced extraction of CTAB microemulsion was due to the electrostatic adsorption of cations with phenol root ions.

Remediation of diesel oil contaminated sand by micro-emulsion

Abstract Micro-emulsion has unique advantages in repairing diesel oil contaminated sand due to its low interfacial tension and strong solubility. By Winsor phase diagram, it was found that with the increase of salinity, the phase of micro-emulsion transformed from Winsor I to Winsor III to Winsor II. Under cryogenic electron microscope, it was observed that Winsor I was O/W type, Winsor II was W/O type, and Winsor III type was bi-continuous type. The effect of inorganic salts, alcohol and temperature on the oil removal rate of diesel oil contaminated sand was investigated by static recovery of micro-emulsion precursor. The results showed that for the anionic micro-emulsion system, with the increase of salinity and alcohols, the oil yield of the upper phase increased first and then decreased, and the two components had a certain compensation effect. For non-ionic micro-emulsion system, with the increase of temperature, the oil yield in the upper phase rose first and then decreased. At the same time, the influence of leaching conditions on oil removal rate was investigated by one-dimensional sand column leaching experiment. It was found that for diesel oil contaminated sand with 15% oil content, when the formulation was 2.00 wt% SDBS, 4.05 wt% n-butanol and 0.40 wt% sodium chloride, the optimum leaching conditions were leaching rate of 4 ml·min−1 and leaching amount of 400 ml. Under such conditions, the oil removal rate was up to 82.84%, that is, the oil content of the sand was reduced to 2.57%. Moreover, the micro-emulsion has good cyclicity, and it can still achieve high oil yield after six cycles.

Design and characterization of selected microemulsions as media for NMR chromatography

NMR chromatography is a promising and superior alternative to NMR spectroscopy for analyzing mixtures since it simultaneously separates the spectra of the compounds and supplies information about their structure. This implies that there is no need for extraction, purification or synthesis of standards, that are expensive, time consuming and usually impractical. The main aim of NMR chromatography is to increase the differences in the diffusivities of different analytes in a mixture, allowing them to be more easily and reliably identified.The selection of surfactants and other components of microemulsions for the best performance as NMR chromatographic media was studied. Attention was focused on the selection of the proper cosolvent in three types of water-dilutable microemulsions: two anionic (deuterated ionic and the previously published fluorinated ionic) and one nonionic (undeuterated Tween-based). The diffusivities of several analytes are compared. The study also examines the effect of dilution and determines the best compositions for the NMR chromatography performance.For the anionic microemulsions, 1-butanol was found to be the most promising cosurfactant in the deuterated system 1-butanol-d10:toluene-d8:SDS-d25 in a 6:3:1 weight-ratio diluted by D2O. This composition, diluted with a 85wt% D2O, formed a microemulsion that was even stable at relatively elevated temperatures (70°C) and can serve as good medium for chromatographic NMR.Another possibility that was studied consists of nonionic-based microemulsions of isopropyl alcohol (IPA) in IPA:toluene:Tween 20 that could also be easily diluted indefinitely with water. IPA was found to be a very efficient cosurfactant at resolving diffusivities of all the components. However, the lack of availability of deuterated Tween makes it impractical for use as an NMR chromatography formulation.

Structure and phase behavior of polymer loaded non-ionic and anionic microemulsions.

We investigate the structure and phase behavior of C12E4 based reverse water in octane microemulsions with small angle x-ray scattering and small angle neutron scattering experiments to explore the phase diagram of the droplet structure. In the regime of stable droplets, these droplets are loaded with the hydrophilic polymer polyethyleneoxide (MW = 1500 g/mol) and compared with microemulsions based on the anionic surfactant AOT. In the small angle neutron scattering experiments, we use shell contrast to focus on the surfactant shell and its variation with addition of polymer. We observe, as predicted by indirect measurements such as dielectric spectroscopy, that the polymer interacts differently with a nonionic or an anionic surfactant shell: In the former case the addition of polymer does not seem to affect the surfactant shell. In the latter case, the obtained scattering data show that the anionic surfactant layer is strongly influenced leading to a higher polydispersity which may be attributed to a floppier surfactant shell.

Alkaline KMnO4 oxidation of reducing sugars in microemulsions: Inhibition effect of surfactants

The kinetics of oxidation of reducing sugars viz. D-glucose and D-fructose by alkaline KMnO4 in microemulsion media was investigated. The aqueous, cationic microemulsion was prepared from cetyl trimethyl ammonium bromide, n-butanol, n-hexane and water, whereas n-decane, aerosol-OT and water were used to prepare the anionic microemulsion. The order of reaction in oxidant was always found to be unity, while that in substrate and alkali was decreased from unity to zero at higher concentrations substrate and alkalirespectively. On decreasing [H2O]/[Surfactant] ratio (increasing surfactant content) in microemulsion, the observed rates constants of oxidation (k obs) were decreased. The inhibition effect on the rate of oxidation was greater in cationic microemulsion. A mechanism consistent with kinetic data is proposed.

High accuracy NMR chemical shift corrected for bulk magnetization as a tool for structural elucidation of microemulsions. Part 2 – Anionic and nonionic dilutable microemulsions

In our previous report we suggested a new analytical tool, high accuracy NMR chemical shift corrected for bulk magnetization as a supplementary tool to study structural transitions and droplet size and shape of dilutable microemulsions. The aim of this study was to show the generality of this technique and to demonstrate that in almost any type of microemulsion this technique provides additional valuable structural information. The analysis made by the technique adds to the elucidation of some structural aspects that could not be clearly determined by other classical techniques.Therefore, in this part we are extending the study to three additional systems differing in the type of oil phase (toluene and cyclohexane), the nature of the surfactants (anionic and nonionic), and other microemulsion characteristics.We studied sodium dodecyl sulfate (SDS)-based anionic microemulsions with different oils and a nonionic microemulsion based on Tween 20 as the surfactant and toluene as the oil phase. All the microemulsions were fully dilutable with water.We found that the change in the slope of chemical shift against dilution reflects phase transition points of the microemulsion (O/W, bicontinuous, W/O). Chemical shift changes were clearly observed with the transition between spherical and non-spherical (wormlike, etc.) droplet shapes. We compared the interaction of cyclohexane and toluene and used the anisotropic effect of toluene’s ring current to determine its preferred orientation relative to SDS.Chemical shifts of the microemulsion components are therefore a useful addition to the arsenal of techniques for characterizing microemulsions.

Anionic microemulsion to solvent stacking for on‐line sample concentration of cationic analytes in capillary electrophoresis

The common SDS microemulsion (i.e. 3.3% SDS, 0.8% octane, and 6.6% butanol) and organic solvents were investigated for the stacking of cationic drugs in capillary zone electrophoresis using a low pH separation electrolyte. The sample was prepared in the acidic microemulsion and a high percentage of organic solvent was included in the electrolyte at anodic end of capillary. The stacking mechanism was similar to micelle to solvent stacking where the micelles were replaced by the microemulsion for the transport of analytes to the organic solvent rich boundary. This boundary is found between the microemulsion and anodic electrolyte. The effective electrophoretic mobility of the cations reversed from the direction of the anode in the microemulsion to the cathode in the boundary. Microemulsion to solvent stacking was successfully achieved with 40% ACN in the anodic electrolyte and hydrodynamic sample injection of 21 s at 1000 mbar (equivalent to 30% of the effective length). The sensitivity enhancement factors in terms of peak height and corrected peak area were 15 to 35 and 21 to 47, respectively. The linearity R(2) in terms of corrected peak area were >0.999. Interday precisions (%RSD, n = 6) were 3.3-4.0% for corrected peak area and 2.0-3.0% for migration time. Application to spiked real sample is also presented.

Screening of microemulsion properties for application in enhanced oil recovery

Microemulsion in enhanced oil recovery is an efficient tool because of its high level of extraction efficiency of residual oil from natural oil reservoir. In the present paper the effect of salinity on anionic microemulsion phase behavior has been investigated by water solubilization method. Interfacial tensions between crude oil and brine, surfactant solution and microemulsion have been measured and it was found that the microemulsion has high ability to reduce interfacial tension. Pseudoternary phase diagram has been established at optimum salinity and composition of single-phase microemulsion has been determined from the curve. Laser light scattering was used to monitor particle size of several microemulsion formulations at different salinities. A series of flooding experiments have been performed using the prepared microemulsions. The additional recoveries were calculated by material balance. Encouraging results with additional recovery more than 25% of original oil in place above the conventional water flooding have been observed. Adsorption characteristics of the surfactant on the sand particles (adsorbent) at different salinities have also been studied.

Evaluation of cyclosporine A eye penetration after administration of liposomal or conventional forms in animal model

A lot of researches have investigated the effects of topical cyclosporine A on the eye surface layers’ diseases. By now the main limitation in cyclosporine application is the low permeation of the drug into the posterior segments of the eye. The aim of present study was to formulate high permeable dosage form can be beneficial in the topical treatment of the uveitis. To reach higher corneal drug absorption and drug concentration in the posterior segments of the eye, 3 nanoliposomal formulations containing 0.5 mg/ml cyclosporine A were prepared. Liposomal formulations and the commercial product (Restasis®) were instilled in the right and left eyes of the rabbits, respectively. The rabbits were killed in the 3, 7, 14 and 28 days of study and the aqueous humor and vitreous were extracted. Mean size of liposomal formulation number 1, number 2 and number 3 were 107.2 ± 0.7, 129.3±0.9 and 144.8±1.8 nm and their zeta potential were -5.0±1.7, -5.5±2.3 and 44.6±6.2 mV, respectively. Results of ocular analysis showed that the liposomal formulations could increase the concentration of the drug in the aqueous and vitreous like Restasis®. But, in contrast with what has been expected the findings of this study implicate nanoliposomal formulations prepared could not make a significant difference in concentration of the drug in aqueous and vitreous humor compared to Restasis® (anionic microemulsion). In conclusion, we can state that liposomes with the same composition as our formulations are not more efficient than microemulsion for cyclosporine as ophthalmic drug delivery.

Synthesis and Characterization of Bimetallic Copper-Gold Nanoparticles

We have synthesized copper-gold, core-shell nanoparticles by the microemulsion method. The particles were prepared in two steps, by first reducing copper ions and then gold ions in the aqueous domains of anionic microemulsions. Two surfactants have been used as emulsifiers, AOT and Cu(AOT)2. The latter is the source of copper ions. Gold ions come from aqueous solutions of HAuCl4. Ultraviolet-visible spectroscopy experiments show that copper nanoparticles are created in the first step of the synthesis, and that a gold layer covers them in the second step. Transmission electron microscopy and related techniques confirm the formation of copper (core)-gold (shell) nanocrystals.

Structural Properties Induced by the Composition of Biocompatible Phospholipid-Based Microemulsion and Amphotericin B Association

Anionic microemulsions (MEs) containing soya phosphatidylcholine, Tween-20, sodium oleate as surfactant, and cholesterol as oil phase were investigated as drug carriers for amphotericin B. Depending on the composition of the microemulsion, various structures, which differently interact with amphotericin B, can be formed. The nanostructured systems were characterized by photon correlation spectroscopy, rheological behavior, and polarized light microscopy. The results reveal that the droplet diameters increased with amphotericin B incorporation for all ranges of surfactant and oil phase. For both amphotericin B-unloaded and amphotericin B-loaded microemulsions, the profile of the oil droplet diameter decreased with increasing the surfactant concentration, demonstrating the stabilizing effect of the surfactant. The increase in the oil phase proportions led to the growth of the droplet diameter, clearly demonstrating the limit of the surfactant organization in the oil-water interface. The amphotericim B incorporation into microemulsion increased with the fraction volume of the oil phase and the surfactant concentration reaching a plateau at high contents. This profile could be quantitatively analyzed by the framework of the pseudo-phase model that considers the amphotericim B distribution between the oil and the aqueous phases. The rheological analysis showed a pseudoplastic behavior with little thixotropic characteristic. Under polarized light, the system of interest showed a dark background characteristic of dispersed droplets. However, for both amphotericim B-loaded and amphotericim B unloaded microemulsions, the increase in the O/S ratio led to the formation of ordered structures with lamellar arrangements.

Structure and viscoelastic behavior of pharmaceutical biocompatible anionic microemulsions containing the antitumoral drug compound doxorubicin

Structure and viscoelastic properties of negatively charged oil-in-water (o/w) microemulsions have been investigated. Microemulsions (ME) containing soya phosphatidylcholine (SPC), eumulgin HRE 40 (EU) and sodium oleate (SO) as surfactant, cholesterol (CHO) as oil phase, and aqueous buffer with and without the antitumoral doxorubicin (DOX) have been studied. The effect of the oil phase/surfactant ratio (O/S) and the DOX incorporation on the structural and rheological properties have been studied in several compositions of ME systems. The rheological analyses were performed through the oscillation stress sweep, creep recovery test, and viscosity test. The combination of the DOX incorporation with the high O/S ratio provided a further viscoelastic structure with linear behavior. Independently of the O/S ratio the oil phase diameter increases according to a sigmoid profile, stabilizing up to 340 min. The apparent viscosity decreases a minimum value with the shear rate, but increases with both the O/S ratio and the DOX incorporation in the system. The structural and rheological properties of the studied MEs were directly dependent on the O/S ratio and can be used to improve the application of the system in the pharmaceutical field.

Synthesis and Characterization of Polystyrene, Poly(butyl acrylate)-Layered Silicates Nanocomposites by Polymerization in Anionic Microemulsions

Styrene (St) and butyl acrylate (BuA) microemulsion polymerizations were investigated in presence of layered silicates (LS) and sodium dodecyl sulfate (SDS) as surfactant. Two main LS categories were used: one in the sodium form as Na montmorillonite (MMT) and the other in organomodified form LS (OLS) with quaternary ammonium salts having different hydrophobic modifiers. The swelling capacity of OLS in presence of monomers with different polarity is more pronounced for partners with closer hydrophobicity to St. The latexes obtained by microemulsion polymerization showed larger particles size for BuA polymer and BuA copolymer with sulfonated styrene than for St. Analyzing the dried hybrid polymers by XRD, we found structures which corresponds to exfoliated LS. The thermal behavior of hybrids, examined by TGA, showed higher rates of decomposing temperatures in the case of OLS, in comparison with the NaMMT hybrids. The obtained hybrids were evaluated by DLS, FTIR, DSC, and SEM.

Crystal hierarchically splitting in growth of BaWO 4 in positive cat–anionic microemulsion

BaWO 4 sheaf-like nanostructures with different degrees of crystal splitting have been synthesized in a cat–anionic positive microemulsion. The solid angle of crystal splitting increases with decreasing surfactant concentration. The non-uniform distribution of surfactants and diffusing of Ba 2+ ions in interface might cause the crystal splitting.

Kinetics of Styrene and Butyl Acrylate Polymerization in Anionic Microemulsions in Presence of Layered Silicates

The effect was studied of various layered silicates (sodium montmorillonite and different organomodified montmorillonites) on kinetics of styrene (St) and butyl acrylate (BuA) in anionic (sodium dodecyl sulfate) microemulsion polymerization. The dependence of the polymerization rate on the conversion exhibits two rate intervals. The presence of layered silicates affects the conversion and polymerization rate of both St and BuA. The size of polymer particles increases with polarity of Cloisite and the increase is more pronounced in poly(butyl acrylate) particles. The kinetic, colloidal and molecular weight parameters are influence both by the monomer and layered silicate polarities. Different approaches (Ugelstadt, Nomura and Gilbert models) were used for evaluation of polymerization kinetics. The desorption constants (kdes) decrease in presence of the studied layered silicates (Cloisite Na, Cloisite 30B, Cloisite 20A). The decreasing values of the desorption constants in the presence of clays; demonstrate a clear effect, which implies the decreasing of the probability of the radical exit from particles in the presence of the layered silicates.

Relationship between structural features and in vitro release of doxorubicin from biocompatible anionic microemulsion

In this work structural features of anionic microemulsions, containing the pharmaceutical biocompatible components soya phosphatidylcholine (SPC), eumulgin HRE 40 (EU) and sodium oleate (SO) as surfactant, cholesterol (CHO) as oil phase and aqueous buffer were studied. Microemulsions were formulated with and without the antitumor drug doxorubicin (DOX). The various microstructures characterized in the pseudo-ternary phase diagram were analyzed by polarized light microscopy, small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) as well as by their ability to incorporate and release DOX. The experimental results demonstrated a correlation between the composition, the structural features and drug delivery. It was found that at higher cholesterol contents, the crystallization of CHO polymorph phases changed the mobility of DOX molecules. Droplets were formed with short-range spatial correlation from a microemulsion (ME) with a low surfactant:oil ratio. More ordered structures with lamellar arrangements formed by the increasing of the CHO proportions in the formulation may be due to CHO crystallization. The in vitro release of DOX showed that the presence of a high content of crystalline CHO prolongs the release of DOX from ME. The retention of DOX in the internal oil phase of the ME may modulate the drug release for a prolonged time. These results clearly demonstrate the potential of ME as a drug-delivery system.

Synthesis and characterization of metallic nanoparticles and their incorporation into electroconductive polymer composites

Abstract Gold and copper–gold nanoparticles were synthesized using anionic microemulsions as reducing reactors. The microemulsions were prepared using sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol OT) and copper(II) bis(2-ethylhexyl)sulfosuccinate (Cu(AOT)2) as surfactants, which were dissolved in isooctane containing an appropriate quantity of water. The growth of nanoparticles was monitored by UV/vis spectroscopy and the nanoparticles formed were characterized by transmission electron microscopy (TEM). The metallic nanoparticles were incorporated into films of an electroconductive polymer (ECP) composite: polyaniline-poly(n-butyl methacrylate) (PANI/PBMA) by the casting technique. The nanoparticle-ECP composite films were characterized by scanning electron microscopy (SEM), electrical conductivity measurements and NH4OH and H2O2-sensing capability experiments. The inclusion of nanoparticles results in a cooperative phenomena between the polyaniline and the nanoparticles and as a consequence, the gold nanoparticles increased the electrical conductivity of the ECP film by two orders of magnitude.

Anionic Microemulsion-Mediated Low Temperature Synthesis of Anisotropic Silicalite-1 Nanocrystals

The low-temperature (368 K) synthesis of silicalite-1 nanocrystals in anionic microemulsions is reported. In the presence of AOT/isooctane mixtures silicalite-1 nanocrystals can be formed that are coffin-shaped and approximately 100 x 40 x 200 nm in size. This is in contrast to samples made without the microemulsion under the same conditions where irregular spherical particles approximately 100 nm in diameter are formed. The current work shows that, in contrast to previous work in this area, the anionic microemulsions cannot stabilize colloidal silica due to the strong repulsive electrostatic forces between the anionic silicate species and the surfactant headgroup. The crystal morphology of the silicalite-1 obtained is also shown to be sensitive to the surfactant identity as syntheses using SDS/heptane/butanol mixtures lead to different morphologies. It is also possible to uncouple zeolite nucleation from growth in these systems. This was demonstrated by adding a solution containing 25 nm silicalite-1 nanocrystals to the AOT/isooctane mixture, which leads to large micron-sized spheres of silicalite-1 containing large mesopores. This report demonstrates that anionic microemulsions lead to fundamentally different crystal habits than the nonionic or cationic microemulsions investigated previously. The future outlook for the use of microemulsion-mediated zeolite growth is also discussed.

A Further Study on the Solubilization Behavior of Styrene in the Cationic Microemulsion Media by Means of NMR

In this study, we further investigated the solubilization of styrene in a cationic CTAB/n‐butanol/water/styrene microemulsion by means of NMR. It was found that the solubilization behavior of styrene in the cationic was quite different from that in anionic microemulsion media. In a cationic microemulsion system, the solubilization site of styrene was mainly in the palisade layer of the microemulsions and less of styrene was located in the inner core. Meanwhile, due to the steric hindrance effect styrene molecules can hardly distribute near the N‐CH3 group of CTAB, and the content of styrene was gradually decreased from the outer to inner along the hydrocarbon chain of CTAB.

Modeling solubilization of oil mixtures in anionic microemulsions: II. Mixtures of polar and non-polar oils

Polar/amphiphilic oils, called lipophilic linkers, are sometimes added to oil–water–ionic surfactant microemulsions in order to increase the solubilization of hydrophobic oils. The solubilization increase has been well documented for a number of systems. However, mathematical models to calculate the solubilization increase have been proposed only for optimum microemulsions (i.e., middle phase microemulsions solubilizing equal volumes of oil and water). In this paper we propose a model, which predicts solubilization enhancement for non-optimum microemulsion systems as well. The model is an extension of the net-average curvature model of microemulsion. The net-average curvature model is combined with a surface activity model to account for the increased palisade layer solubilization due to the presence of the polar/amphiphilic oil component. New non-linear mixing rules are also incorporated to account for the optimum salinity and the characteristic length variation of the anionic surfactant microemulsion as a function of the lipophilic linker concentration. The model predicts the effect of the lipophilic linker and the electrolyte concentration on the oil solubilization in accordance with the experimental results.