Mixed Reverse Micelles Research Articles

Study of Structure of Water Droplets of Nonionic Polyoxyethylene (4) Lauryl Ether Reverse Micelles in the Presence of Sodium Cholate

Abstract The microenvironment of water droplets of nonionic polyoxyethylene (4) lauryl ether reverse micelles was investigated with infrared and ultraviolet-visible spectroscopy, also by viscosity and dynamic light scattering measurements in the presence of biological surfactant sodium cholate as additive. Influence of concentrations of polyoxyethylene (4) lauryl ether and sodium cholate on the microstructure of mixed reverse micelles was studied. Influence of sodium cholate as additive on the ratio of free, bound and trapped water fractions was studied via deconvolution of the O-H stretching vibrational absorption spectra in the region of 3 000–3 800 cm−1 into three subpeaks with a Monte Carlo method. Several characteristic parameters of reverse microemulsions were calculated on the basis of measurements of their kinematic viscosity. A different influence of concentration of sodium cholate on the binding constant and association degree of optical probes (o-nitroaniline and methyl orange respectively) to ethylene oxide groups of nonionic surfactant was observed. It was found that the bound water fraction, the binding constants and association degrees, the relative density of water pockets, etc. change their values passing through an extremum under the influence of sodium cholate.

Structure of Mixed Reverse Microemulsions Based on Sodium Bis (2‐Ethylhexyl) Sulfosuccinate and Sodium Cholate

AbstractThe microenvironment of water droplets of sodium bis (2‐ethylhexyl) sulfosuccinate (AOT) and sodium cholate mixed reverse microemulsions was studied. Structural changes of water pockets in mixed reverse micelles were investigated by IR spectroscopy. The O‐H stretching vibrational absorption spectra in the region of 3000–3800 cm−1 were fit to three subpeaks with the Monte Carlo method. It was revealed that additives of sodium cholate suppress free water fraction in the water droplets of reverse micelles from 31% to 20% and support rising of bound fraction from 53% to 65%. The binding of optical probe ortho‐nitroaniline to the mixed reverse micelles was determined by UV–visible spectroscopy. It was found that introducing of additives of sodium cholate below its critical micelle concentration (CMC) causes increasing of values of binding constant Kb twice compared with reverse micelles modified with pure water. However, values of the binding constant were reduced 4‐fold at concentrations of sodium cholate higher than its CMC. Electrical conductivity of the reverse mixed micellar solutions (AOT + sodium cholate) was measured. Water‐induced percolation in conductance of mixed reverse microemulsions occurs at a lower value of water/surfactant molar ratio (W) under the influence of sodium cholate, viz. electrical percolation threshold decreases from W = 32 to W = 15. The size of water droplets was estimated with the dynamic light scattering method. It was found that additives of sodium cholate below and higher than the CMC results in increasing and decreasing of hydrodynamic diameters of the water droplets, respectively, but sizes of water droplets decrease at concentrations of sodium cholate higher than its CMC.

Nanoparticle charging with mixed reverse micelles in apolar media

The charging of colloidal particles using mixed surfactants in apolar media is investigated. Previous work has shown that one can predict the sign and magnitude of particle charge by comparing the acid-base properties of an oil-soluble surfactant to the acid-base properties of a specific particle. The present work sought to tune the acid-base properties by using mixed surfactants. Unexpected mineral oxide particle charging results were obtained however, from mixing the acidic surfactant sorbitan monooleate (SPAN 80), with the basic surfactant polyisobutylene succinimide (OLOA 11000), requiring further investigation into the mixed reverse co-micelle particle charging mechanism. Conductometric titrations and small-angle neutron and x-ray scattering measurements showed that the surfactant mixtures formed spherical reverse co-micelles. Quartz crystal microbalance adsorption measurements demonstrated that both surfactants can adsorb to the particle surface. Lastly, electrophoretic mobility measurements showed that the surfactant mixture produced negative particle charging for nearly all surfactant ratios, and a greater magnitude of negative charging than that produced by the OLOA 11000 surfactant alone. It was discovered that in the mixed surfactant system studied, the basic surfactant would charge the hydroxyl groups on both the oxide surface, and the adsorbed acidic surfactant head groups. The results showed that particle charging behavior in apolar media using mixed micelles requires knowledge beyond that for the individual surfactants and their proportions in the mixture.

Reverse micellar modified mixed anionic and zwitterionic surfactant system for antibiotic extraction

A reverse micellar was modified by combining the anionic AOT and zwitterionic lauryl sulfobetaine surfactant for the extraction of erythromycin was proposed for the first time as a new approach for antibiotic extraction. The stability of the mixed reverse micelle was evaluated in terms of the critical micelle concentration (CMC) using the Wilhelmy Ring method, as well as the thermodynamic properties prior to extraction. The effect of parameters such as AOT concentration, lauryl sulfobetaine fraction and pH of the aqueous phase was investigated during forward extraction. Isopropanol volume percent (%), NaCl concentration, and pH of aqueous phase were investigated during backward extraction. The thermodynamic analysis confirmed the stability of the mixed AOT/lauryl sulfobetaine reverse micelle with a positive synergistic effect. The surface activity was enhanced, by which the CMC of the mixed reverse micelle was significantly lowered, ranging from 0.7 to 5.7 g/L. The overall thermodynamic data comprising ΔGm (between −15.44 and −20.24 kJ/mol), ΔGads (between −27.03 and −28.97 kJ/mol), and ΔGoex (range between −0.39 and 8.87 kJ/mol) are affirmative that micellization was spontaneous. Erythromycin was also found to be interfacially active at all tested condition. The highest erythromycin solubilisation (94.2%) was achieved, even with low AOT surfactant (60.0 g/L) which reflects the synergy between AOT and lauryl sulfobetaine. In addition, in the absence of isopropanol, erythromycin was found to be successfully recovered during the backward extraction. However, isopropanol is still considered as a recovery booster which enables higher erythromycin recovery.

Partitioning isotherm and kinetic of erythromycin into mixed reverse micelle during forward transfer

The capacity of AOT (sodium bis (2-ethylhexyl) sulfosuccinate) and SB3-12 (3-(N, N-dimethyldodecylammonio) propanesulfonate) mixed reverse micelle for erythromycin adsorption was assessed using the Langmuir, Freundlich, and Sips isotherm models. The kinetic of erythromycin transport was also evaluated using the two-film model. The results indicated that the Langmuir isotherm model exhibits the highest precision based on the regression coefficient data, however, this applies only for the condition of 80.0 to 160.0 g/L of AOT concentration. Error analysis revealed that for a condition where AOT concentration was low, the process fits the Freundlich isotherm model, suggesting that at a surfactant concentration around 20.0 g/L, forward transfer of erythromycin shows physisorption criteria. The Langmuir isotherm data for higher AOT concentration (80.0 g/L) denotes the chemisorption characteristics, by which erythromycin transfer was at the highest degree. This also signifies that high AOT concentration is a favourable condition where stable mixed reverse micelle was available and erythromycin adsorption was accelerated. In addition, the kinetic data complements the two-film theory for a flat interface model and shows that dissemination of erythromycin into the interfacial layer of mixed reverse micelles depended on surfactant concentration. Overall, this study confirms previous findings and contributes additional evidence for erythromycin extraction, under the influence of anionic-zwitterionic surfactant combination and shows superiority towards solubilising biomolecules.

Isooctane-based anionic and zwitterionic surfactant: Synergistic interaction of mixed reverse micelle and solubilisation of erythromycin

In the present study, the reverse micelle of anionic (sodium bis(2-ethylhexyl) sulfosuccinate) (AOT) and zwitterionic (3-N, N-Dimethyllaurylammonio propanesulfonate) (SB3–12) surfactants was mixed in an isooctane organic phase, and their behaviour towards solubilisation of erythromycin was investigated. Erythromycin is used as an alternative for gram-positive infections in patients resistant to, or allergic to penicillin for skin treatment, soft tissue infection, mycoplasma pneumonia and legionella disease. The critical micelle concentration of the mixture (CMCmix) was analysed by applying phase separation and Rubingh's model of the surfactants to evaluate the synergistic effect between AOT and SB3–12 in isooctane solution. The critical micelle concentration of AOT and SB3–12 was 22.5 g/L and 0.9 g/L, respectively in isooctane phase. The critical micelle concentration of the mixed AOT/SB3–12 reverse micelle was 0.70 g/L. The mixed reverse micelle has efficiently increased the solubility of erythromycin, by which 94.2% transfer was achieved from 0.8:0.2 proportion of AOT to SB3–12. Thermodynamic parameters describing the free energy of micelle formation (ΔGm) and standard Gibbs free energy of adsorption (ΔGads) were found to be negative which suggest that micellization and adsorption were spontaneous. The excess Gibbs free energy of mixing (ΔGoex) value indicates that the formation of the AOT/SB3–12 mixed reverse micelle was thermodynamically stable. Conclusively, the mixed reverse micelle enhances erythromycin solubilisation in isooctane organic phase at low surfactant concentration, and the synergism of the combination between AOT and SB3–12 was positive.

Silver nanoparticles stabilized by AOT and Tergitol NP-4 mixture: Influence of composition on electrophoretic concentration, properties of concentrated organosols and conductivity of films

A comparative analysis of the main physico-chemical characteristics of silver nanoparticles produced in mixed reverse micelles of nonionic surfactant Tergitol NP-4 with addition of anionic AOT was carried out. The nanoparticles are shown to have a positive electrokinetic potential. The only exception is nanoparticles synthesized in Tergitol NP-4 reverse micelles without addition of AOT, which have a zero electrokinetic potential. An increase in AOT concentration in the mixture leads to a decrease in the size of particles produced and an increase in the electrokineticpotential. It was shown that silver nanoparticles with close to quantitative extraction rates can be concentrated by non-aqueous electrophoresis with AOT content in mixture equaled 5 mol% and more. For mixture with content of AOT more than 50 mol%, no concentration is observed for surfactants. In the systems with high content of Tergitol NP-4 an increase in the concentration of surfactants is observed compared to the starting organosol. A decrease in AOT concentration leads to a decrease in the stability of the nanoparticles that results in a reversible change in the surface plasmon resonance spectra of nanoparticles under drying and irreversible agglomeration of nanoparticles with a decrease in the surfactant concentration. The presence of reversible agglomeration of the nanoparticles is likely due to the strong negative effect of Tergitol NP-4 on the stability as well as the conductivity and adhesion of coatings produced by thermolysis of the nanoparticle concentrate.

The influence of cholesterol on the generation of radicals in mixed reverse micelles of cationic surfactants with hydroperoxides

Cationic surfactants (S+) and acetylcholine (ACh), the most important neurotransmitter playing an essential role in the neuromuscular and cognitive activity of living beings, form mixed reverse micelles with hydroperoxides (ROOH) in organic media, where ROOH decay into free radicals is catalytically accelerated. Adding cholesterol (Chol, 30 mol.%) to pyridinium (СРВ) and cetyltimethylammonioum (СТАВ) bromides, reduces the radical generation rate in ROOH catalytic decay several times. However, a higher radical initiation rate is observed in the case of less ordered and larger ACh–ROOH reverse micelles. A Chol additive does not essentially affect the size of СТАВ and СРВ micelles with hydroperoxides but results in their decrease in the case of ACh–ROOH.

Construction of Surfactin--Polysorbate-80 reversed micelle systems and its application on extraction of cellulasee

This work studied a novel method to construct a mixed reverse micelle system and its application in extracting and purifying enzymes. Mixed reversed micellar extraction formed by biosurfactant surfactin and ionic surfactant polysorbate-80 was applied for extracting cellulase. 40% surfactin and 60% polysorbate-80 were found to be the best system. The activity and protein recovery were obtained with the best conditions: in forward extraction, surfactant concentration was 3.0 mM; pH 7.0; temperature 40°C; KCl 0.05 M. In backward extraction, pH 7.5; temperature 40°C; KCl 0.1 M.

Structural Properties of Span 80/Tween 80 Reverse Micelles by Molecular Dynamics Simulations.

The sorbitan monooleate (Span 80)/poly(oxyethylene) sorbitan monooleate (Tween 80) reverse micelles (RMs) in the water-in- n-decane microemulsion were studied using the molecular dynamics simulation. The coexistence of the large RMs with the hydrodynamic radii Rh ∼ 10-20 nm and small RMs with Rh ∼ 1-2 nm was previously specified for this system. Models of both surfactants and decane were based on the united-atom approach to allow us to describe the structural properties of the small RMs. The micelles have been self-assembled from an initially homogeneous mixture of surfactant, water, and decane molecules. The dependence of the shape of the RMs on the relative content of surfactants has been established. The inner structure of Span 80, Tween 80, and Span 80/Tween 80 RMs was quantitatively described. Tween 80 molecules penetrate the water core, whereas Span 80 molecules are located on the surface of the RM. The obtained data show that the hydrogen bonds are formed between the surfactant molecules on the surface of the RM and play an important role in the formation of RMs. The water hydrogen bond density distribution in individual and mixed RMs explains the advantages of the mixed surfactant system compared to an individual surfactant.

Structural Characterization of Biocompatible Reverse Micelles Using Small-Angle X-ray Scattering, 31P Nuclear Magnetic Resonance, and Fluorescence Spectroscopy

The most critical problem regarding the use of reverse micelles (RMs) in several fields is the toxicity of their partial components. In this sense, many efforts have been made to characterize nontoxic RM formulations on the basis of biological amphiphiles and/or different oils. In this contribution, the microstructure of biocompatible mixed RMs formulated by sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) and tri- n-octylphosphine oxide (TOPO) surfactants dispersed in the friendly solvent methyl laurate was studied by using SAXS and 31P NMR and by following the solvatochromic behavior of the molecular probe 4-aminophthalimide (4-AP). The results indicated the presence of RM aggregates upon TOPO incorporation with a droplet size reduction and an increase in the interfacial fluidity in comparison with pure AOT RMs. When confined inside the mixed systems, 4-AP showed a red-edge excitation shift and confirmed the increment of interfacial fluidity upon TOPO addition. Also, the partition between the external nonpolar solvent and the RM interface and an increase in both the local micropolarity and the capability to form a hydrogen bond interaction between 4-AP and a mixed interface were observed. The findings have been explained in terms of the nonionic surfactant structure and its complexing nature expressed at the interfacial level. Notably, we show how two different approaches, i.e., SAXS and the solvatochromism of the probe 4-AP, can be used in a complementary way to enhance our understanding of the interfacial fluidity of RMs, a parameter that is difficult to measure directly.

The solubilization and extraction parameters of erythromycin from aqueous phase into mixed AOT/SB3-18 reverse micelle phase

<p>A liquid anionic-zwitterionic surfactant-based aqueous two-phase extraction was developed and applied for the extraction of erythromycin. Erythromycin solubilization from aqueous to reverse micelle phase was studied. Zwitterion SB3-18 surfactant was added to ionic solution of bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) to form an organic mixed micellar phase. Erythromycin was then added to the mixtures and two clear phases were formed. The parameters affecting erythromycin solubilization including AOT concentration (20.0 ̶ 120.0 g/L), zwitterion concentration (6.0 ̶ 16.0 g/L), NaCl concentration (0.0 ̶ 25.0 g/L) and aqueous pH (6.0 ̶ 9.0) were investigated via statistical software. Solubilization of erythromycin into mixed reverse micelle could be easily evaluated by the measurement of erythromycin concentration in the organic phase. The results showed that AOT and zwitterion concentration governed the erythromycin solubilization by a factor of 4.562 based on the Pareto chart.</p><p>Chemical Engineering Research Bulletin 19(2017) 123-128</p>

MATHEMATICAL MODELLING OF BACKWARD EXTRACTION MIXED REVERSE MICELLE OF AMOXICILLIN BY SURFACE RESPONSE METHODOLOGY (RSM)

One of important factor in reverse micelle extraction is backward transfer. It is important to investigate the favourable conditions for backward transfer from reverse micellar phase to an organic phase. The back extraction of amoxicillin was studied using mixed reverse micelle with combination sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and TWEEN 85. Backward extraction was optimized via response surface methodology (RSM). For mathematical modelling, Central Composite Design (CCD) was used to studies the significant of independent variables: pH of stripping solution (5-8), KCl concentration (2.0 -16.0 g/L) and backward extraction time (5-35 minutes) on the response of the process. Optimized backward extraction for maximized final mass of amoxicillin extracted into aqueous were pH of stripping solution (6.58), backward time (19.8 minutes) and concentration of KCl (11.02 g/L) on the response of the process. Result showed that the experimental data was fitted well to a second-order polynomial model.

Thermodynamic Description of Synergy in Solvent Extraction: I. Enthalpy of Mixing at the Origin of Synergistic Aggregation.

Revisiting aggregation of extractant molecules into water-poor mixed reverse micelles, we propose in this paper to identify the thermodynamic origins of synergy in solvent extraction. Considering that synergistic extraction properties of a mixture of extractants is related to synergistic aggregation of this mixture, we identify here the elements at the origin of synergy by independently investigating the effect of water, acid, and extracted cations. Thermodynamic equations are proposed to describe synergistic aggregation in the peculiar case of synergistic solvent extraction by evaluating critical aggregation concentration (CAC) as well as specific interactions between extractants due to the presence of water, acid and cations. Distribution of two extractant molecules in the free extractants and in reverse micelles was assessed, leading to an estimation of the in-plane interaction parameter between extractants in the aggregates as introduced by Bergström and Eriksson ( Bergström, M.; Eriksson, J. C. A Theoretical Analysis of Synergistic Effects in Mixed Surfactant Systems . Langmuir 2000 , 16 , 7173 - 7181 ). Based on this model, we study the N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA) and di(2-ethylexyl) phosphoric acid (HDEHP) mixture and show that adding nitric acid enhances synergistic aggregation at the equimolar ratio of the two extractants and that this configuration can be related to a favored enthalpy of mixing.

The mixing behaviour of anionic and nonionic surfactant blends in aqueous environment correlates in fatty acid ester medium

Mixtures of dissimilar surfactants can have superior properties compared to those of the individual surfactant components involved, which provide impetus for research on interactions between surfactants. It was also demonstrated that a change in the composition of external phase promotes remarkable changes in interfacial properties of reverse micelles (RMs), which are crucial to understand the system in order to use them as nanoreactors. Hence, it should be achievable to explore the influence of non-ionic Tween-85 on the properties of anionic AOT based micelle as well as RMs in fatty acid esters [e.g., ethyl myristate (EM), ethyl palmitate (EP) and ethyl oleate (EO)]. A comprehensive micellization behavior is studied at different mixed compositions (XTween-85) by surface tension method. Non-ideal mixing behaviors along with synergistic interaction between the constituent surfactants in the mixed micelles are evidenced. Mixed micelles illustrate favorable micellization behavior in terms of thermodynamic parameters. Further, fatty acid ester medium-based mixed RM shows synergism in water solubilization capacity. Microstructures of these systems are investigated by conductance, DLS, and FTIR studies. The solvation and rotational relaxation dynamics using picosecond time-resolved emission spectroscopy (TRES) is used to investigate the effect of XTween-85 as well as chemical architecture of fatty acid esters for the first time on the excited state dynamics of fluorophore. The solvation dynamics is found to be faster with an increase in XTween-85 and the average solvation time follows the order, EO<EP<EM, which collaborates well with droplet size and abundance of bulk-like water. Anisotropy studies reveal a decrease in the rotational restriction on the probe for EO based RMs. It is reasonable that this work have the potential to serve as good biomimicry models to study various processes occurring in biological molecules embedded in biomembranes.

Nanoscale Control Over Interfacial Properties in Mixed Reverse Micelles Formulated by Using Sodium 1,4‐bis‐2‐ethylhexylsulfosuccinate and Tri‐n‐octyl Phosphine Oxide Surfactants

The interfacial properties of pure reverse micelles (RMs) are a consequence of the magnitude and nature of noncovalent interactions between confined water and the surfactant polar head. Addition of a second surfactant to form mixed RMs is expected to influence these interactions and thus affect these properties at the nanoscale level. Herein, pure and mixed RMs stabilized by sodium 1,4-bis-2-ethylhexylsulfosuccinate and tri-n-octyl phosphine oxide (TOPO) surfactants in n-heptane were formulated and studied by varying both the water content and the TOPO mole fraction. The microenvironment generated was sensed by following the solvatochromic behavior of the 1-methyl-8-oxyquinolinium betaine probe and (31) P NMR spectroscopy. The results reveal unique properties of mixed RMs and we give experimental evidence that free water can be detected in the polar core of the mixed RMs at very low water content. We anticipate that these findings will have an impact on the use of such media as nanoreactors for many types of chemical reactions, such as enzymatic reactions and nanoparticle synthesis.

Modulation of anionic reverse micellar interface with non-ionic surfactants can regulate enzyme activity within the micellar waterpool

In this contribution, we have studied the effect of replacing anionic surfactant 1,4-bis(2-ethylhexyl)sulphosuccinate (AOT) by nonionic surfactant(s) of varying hydrophilic-lipophilic balance (HLB) on the structure, dynamics and activity of water encapsulated in reverse micelles (RMs) formed in a biocompatible oil isopropyl myristate (IPM). The sizes of the RM droplets are measured using dynamic light scattering (DLS) technique, while the structure of water in the RM waterpool is determined using FTIR spectroscopy. The solvation dynamics in these systems is obtained by time-resolved fluorescence spectroscopy using ammonium 8-anilino-1-naphthalenesulfonate (ANS) as the fluorophore. We spectroscopically measure the enzymatic activity of α-chymotrypsin on the substrate Ala-Ala-Phe-7-amido-4-methyl-coumarin (AMC) in these mixed RM systems. It has been found that the rate could either be enhanced or reduced depending on the HLB of the added Brij(s). Such result could be found useful in modulating the reaction for specific applications.

Mixed reverse micellar extraction and effect of surfactant chain length on extraction efficiency

Abstract This study investigated the effect of surfactant chain length on mixed reverse micellar extraction of cellulase. The mixed reverse micelle systems were formed by biosurfactant rhamnolipid and a nonionic surfactant tween (tween-20, tween-40, tween-60, or tween-80). Electron spin resonance (ESR) method was used in order to find the suitable chain length of tween and the best ratio of rhamnolipid/tween mixture. The key parameters such as pH and temperature in forward and backward extraction were studied, and the results showed that mixed reverse micelle with different surfactant chain length had different pH sensitivities. Rhamnolipid/tween-80 system was more sensitive to pH than other systems, and rhamnolipid/tween-20 system was the least sensitive to pH among four systems. The experimental results also showed that chain length had limited sensitivity to temperature. Rotation correlation time of cellulase solutions (original and extraction) were investigated, which proved the superiority of longer chain length system (rhamnolipid/tween-80 system).

Magnetic effects in hydroperoxide decomposition in mixed micelles with cationic surfactants

The retardation effect of oxygen and external magnetic field on the yield of radicals in hydroperoxide decomposition in catalytic nanoreactors was discovered. Mixed reverse micelles formed by the cationic surfactants (Surf) and hydroperoxide {mLOOH...nSurf} play the role of nanoreactors. Similar effects of oxygen and external magnetic field (60–150 mT) on the yield of radicals are observed in the catalytic decomposition of hydroperoxide in the presence of acetylcholine. It is noteworthy that the retardation effect of the magnetic field decreases in the presence of paramagnetic particles such as oxygen and relatively stable radicals.

Dyeing properties of CI reactive violet 2 on cotton fabric in non-ionic TX-100/Span40 mixed reverse micelles

In order to improve the dyeing properties of reactive dyes onto cotton fabric in reverse micelles, non-ionic mixed reverse micelles were prepared using non-ionic TX-100 and Span40 as a dyeing media. The maximum water solubilization, diameter of water pool, aggregation density, and conductivity values of the reverse micelles with different concentrations of TX-100/span40 were measured and compared. The adsorption and dyeing capacity of reactive dyes on cotton fabric in reverse micelles were investigated. Additionally, the Lagergren first-order equation and the pseudo second-order equation were also employed to fit the experimental data. The results indicated that the diameter of water pool and packing density of reverse micelles were increased with an increasing amount of Span40, which caused lower conductivity. The repelling force and competitive adsorption between the dyes and cotton fabric were decreased with an increasing amount of Span40, and the higher adsorption and improved dyeing properties in reverse micelles were obtained. Moreover, the dye adsorption process in mixed TX-100/Span40 reverse micelles could be described using pseudo-second-order kinetic equations. The adsorption is a chemical process.