Ternary Microemulsion System Research Articles

Construction of zwitterionic surfactant-stabilized hydrophobic ionic liquid-based bicontinuous microemulsion and microstructure-dependent activity of solubilized lipase

In the present work, the sulfobetaine-type zwitterionic surfactant (SB-n) was tried for the first time to construct hydrophobic ionic liquid (HIL)-based bicontinuous microemulsions. The composition-dependent phase behavior of the HIL/water (buffer)/SB-n ternary microemulsion system was determined by the method of T-γ fishlike phase diagram. It is found that the phase inversion temperature increases markedly with the increase of the alkyl chain length (n) of SB-n, but the surfactant efficiency changes little. The HIL greatly affects the phase behavior, depending on the ion structure. It is found that the SB-12 stabilized [C8mim][PF6]-based microemulsion system has moderate phase inversion temperature, and moreover, its surfactant efficiency is the highest among the reported HIL-based bicontinuous microemulsions stabilized by conventional surfactants. The composition-dependent microstructure of the SB-12-stabilized [C8mim][PF6]-based bicontinuous microemulsion was characterized by SAXS technique, and its influence on the catalytic performance of solubilized lipase was also explored. With the increase of the mass ratio of the HIL to water (α), the correlation length (ξ) changes slightly, but the microdomain size (d) decreases steadily. Unlike α, with the increase of the surfactant concentration (γ), the d changes little, but the ξ increases markedly. This abnormal change of ξ with γ should be ascribed to the interface rigidity of the microemulsion. The catalytic efficiency of lipase depends on the rigidity of the interface and its interfacial area. The above original studies not only enrich HIL-based microemulsion systems, but also provide scientific support for lipase-based green synthesis and transformation.

Phase behavior and microstructure of sugar surfactant-ionic liquid microemulsions

Microemulsions have been explored as a unique and versatile reaction media for a variety of chemical reactions, viz. nanoparticle preparation, organic synthesis, bio-organic synthesis etc. The phase behavior and microstructure of a ternary system water/1-butyl-3-methylimidazolium hexafluorophosphate/Sugar Surfactant was studied as a function of temperature and sugar surfactant mass fraction, γ. In the present study, a hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was used to replace commonly used organic solvents (n-alkanes) as an oil/non-polar phase substitute in ternary microemulsion formulations, wherein, a sugar based alkyl polyglycoside nonionic surfactant was used instead of a conventional nonionic surfactant (i.e., alkyl polyoxyethylene ether class) to solubilize hydrophobic ionic liquid and water. The effect of alkanols of variable chain length (octanol, decanol and dodecanol) as co-surfactant on the phase behavior and microstructure of ionic liquid/sugar surfactant/water ternary microemulsion systems was also investigated. The ability of nonionic sugar-based surfactant n-decyl β-D-maltoside, and n-dodecyl β-D-maltoside, to solubilize oil (hydrophobic ionic liquid) and water, i.e., was evaluated. Moreover, phase behavior and microstructure of ternary systems, 1-butyl-3-methylimidazolium tetrafluoroborate:water (1:1)/sugar surfactant/n-alkanes (alkanes of varying chain length, i.e., octane, decane and dodecane) was also studied. Solubilization of a water insoluble dye, Sudan Red, in selected microemulsion systems was also investigated.

Using carbonaceous nanoparticles as surfactant carrier in enhanced oil recovery: A laboratory study

Carbonaceous nanoparticles multi-walled carbon nanotubes (MWNTs) and carbon blacks (CBs) exhibit promising properties for potential applications in crude oil production. The combination of large specific surface area and the strong affinity toward surfactants of nanoparticles mark their candidacy for delivering surfactant deep inside the reservoir. This study is aimed to assess the feasibility of surfactant carriers in tertiary oil recovery. Stable dispersions of aqueous-phase MWNTs or CBs that are formulated and able to propagate through the reservoir medium (3 wt% brine and 60 °C) were first examined as a prerequisite for reservoir application. Competitive adsorption of surfactant on nanoparticles was beneficial to decrease adsorptive loss on Ottawa sand at equilibrium concentration below critical micelle concentration (CMC). As a proof of concept, phase behavior of a ternary surfactant microemulsion system confirmed that the chosen nanoparticles (100 mg/L) successfully delivered surfactants and spontaneously released them to the O/W interface. The observed phenomenon is in accordance with calculation of the Gibbs free energy associated with oil/water/surfactant system. Besides, surfactants carried by nanoparticles achieved equilibrium ultralow interfacial tension between excess oil and aqueous phase similar to the value of surfactant-only formulation (0.007–0.009 mN/m). In one-dimensional sand pack tests, injection of MWNT-surfactant blend achieved faster and higher tertiary recovery than surfactant-only formulation, with cumulative tertiary oil recovery of 42.7% versus 38.1%. It has been noticed that once surfactant been released, destabilization of nanoparticle dispersion occurred and thus increased their retention in porous medium. In case of tight formations, further improvements may be addressed by applying functionalized carbonaceous nanoparticles to assure their transport in porous media after release of surfactant.

Synthesis of copper nanoshales from a Triton™ X-100/cyclohexane/water ternary microemulsion system

Shale-like copper nanostructure was synthesized for the first time from a water-in-oil microemulsion medium comprising Triton? X-100/cyclohexane/water ternary system. The nanoshales were synthesized through chemical reduction by hydrazinium hydroxide in alkaline medium. The nanoshales were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) patterns.

Studies on formation and percolation in ionic liquids/TX-100/water microemulsions

Ternary microemulsion systems of H2O/Triton X-100/[BMIM][Tf2N], and H2O/Triton X-100/[BMIM][PF6] were prepared, compared and characterized for phase behavior for different water/surfactant ratios, at 25°C. It was found that a change of an anion structure in the ionic liquids determines the total monophasic area of the systems. A liquid crystalline mesophase was detected in H2O/Triton X-100/[BMIM][PF6]. The microemulsion domains were identified by means of conductivity, viscosity and dynamic light scattering measurements. An increase in water mass fraction resulted in an increase of electrical conductivity of both systems, however not as rapid as in typical microemulsion systems. The conductivity data were analyzed in terms of percolation theory, and it was revealed, that the theory may be adopted only partially. The variations of the dynamic viscosity of surfactant/IL mixtures, as a function of water mass fraction along the experimental dilution lines, differ significantly from typical solvent based microemulsions. The size of water/IL microemulsion droplets, measured by dynamic light scattering, is nearly independent on the content of water.

Physico-chemical studies on ionic liquid microemulsion: Phase manifestation, formation dynamics, size, viscosity, percolation of electrical conductance and spectroscopic investigations on 1-butyl-3-methyl imidazolium methanesulfonate + water/Tween 20 + n-pentanol/n-heptane pseudoternary system

Combined phase behavior, method of dilution, viscosity, dynamic light scattering, electrical conductance and spectroscopic probing techniques were employed in understanding the physicochemical properties of pseudo ternary microemulsion system 1-butyl-3-methyl imidazolium methanesulfonate ([bmim][MS]±water)/(Tween 20+n-pentanol)/n-heptane. Phase manifestation revealed that the area under the clear region depended on ionic liquid (IL)/water mole ratio. Thermodynamic and structural parameters for the formation of (IL+water)-in-oil μE system were evaluated employing the method of dilution at different [polar domain]/[Tween 20] mole ratio and temperature; the parameters depended on the composition of the polar domain. IL+water comprising μE behaved differently, compared to the conventional water-in-oil μE system, especially at higher mole fraction of IL. Both the size and viscosity increased with the increasing volume fraction of the dispersed phase (IL+water), while they decreased with increasing temperature. Although having IL, the μEs were less conducting due to the strong interaction between the IL cation and the oxyethylene groups of the surfactants. Formation of micelle like aggregates within the polar domain further suppressed the conductivity. Combined studies on the absorption and emission spectra of eosinY, along with the excited state lifetime and anisotropy measurements, revealed the existence of different states of IL+water in the polar domain.

Critical Behavior of {DMA + AOT + n-Octane} Nonaqueous Microemulsion with the Molar Ratio (ω=2.66) of DMA to AOT

To examine the critical behavior of the nonaqueous microemulsion, we have determined the coexistence curves of (T,n),(T,φ) and (T,ψ) (n,φ,ψ are the refractive index, the volume fraction, and the effective volume, respectively) for a ternary microemulsion system of {N,N-dimethylacetamide (DMA) + sodium di-(2-ethylhexyl) sulfosuccinnate (AOT) + n-octane} with the molar ratio 2.66 of DMA to AOT by measuring the refractive index at constant pressure within about 7 K from the critical temperature Tc. The critical exponents β and critical amplitudes B have been deduced from (T,n), (T,φ) and (T,ψ) coexistence curves; the critical exponents β are in good agreement with 3D-Ising exponent for the ternary system. The experimental results have been analyzed to examine the diameters of the coexistence curves, and to discuss the goodness of density variables for constructing order parameters.

Critical Behavior of {Water + AOT + Decane} Microemulsion with Small Molar Ratio of Water to AOT

The coexistence curves of (T,n), (T,φ) and (T,ψ) (n,φ,ψ are the refractive index, the volume fraction, and the effective volume fraction, respectively) for a ternary microemulsion system of {water + sodium di(2-ethylhexyl) sulfosuccinate (AOT) + n-decane} with the molar ratio 25.1 of water to AOT have been determined at constant pressure within about 7 K from the critical temperature Tc by measurements of refractive index. The critical exponent β has been deduced from the (T,n), (T,φ) and (T,ψ) coexistence curves within 1 K above Tc. They were 0.323, 0.327, and 0.329, respectively, and were consistent with the 3D-Ising value. Furthermore, the experimental results have been analyzed to obtain critical amplitudes B and the Wegner-correction terms B1, to examine the diameters of the coexistence curves and to discuss the goodness of density variables for constructing order parameters.

Phase Behavior and Kinetics of Phase Separation of a Nonionic Microemulsion of C12E5/Water/1-Chlorotetradecane upon a Temperature Quench

The phase behavior and phase separation kinetics of a model ternary nonionic microemulsion system composed of pentaethylene glycol dodecyl ether (C12E5), water, and 1-chlorotetradecane were studied. With increasing temperature, the microemulsion exhibits the following rich phase behavior: oil-in-water phase (L1+O), droplet microemulsion phase (L1), lamellar liquid crystalline phase (Lproportional), and sponge-like (liquid) phase (L3). The microemulsion with a fixed surfactant-to-oil volume fraction ratio (Phis/Phio) of 0.81 and droplet volume fraction of 0.087 was perturbed from equilibrium by a temperature quench from the L1 region (24 degrees C) to an unstable region L1+O (13 degrees C), where the excess oil phase is in equilibrium with the microemulsion droplets. The process of phase separation in the unstable region was followed by time-resolved small-angle X-ray scattering (TR-SAXS) and time-resolved turbidity methods. Due to the large range of scattering vector (q=0.004-0.22 A(-1)) that is possible to access with the TR-SAXS method, the growth of the oil droplets and shrinking of the microemulsion droplets as a result of phase separation could be studied simultaneously. By using an advanced polydisperse ellipsoidal hard-sphere model, the experimental curves have been quantitatively analyzed. The microemulsion droplets were modeled as polydisperse core-shell ellipsoidal particles, using molecular constraints, and the oil droplets are modeled as polydisperse spheres. The radius of gyration (Rg) of the growing oil droplets, volume fraction of oil in the microemulsion droplets, and polydispersity were obtained from the fit parameters. The volume equivalent radius at the neutral plane between the surfactant head and tail of the microemulsion droplet decreased from 76 to 51 A, while the radius of oil drop increased to 217 A within the 160 min of the experiment. After about 48 min from the temperature quench, the system reaches a steady state and continues to coarsen at a constant fraction of the oil of 0.51 in the oil phase by Ostwald ripening with the power law dependence of Roil proportional, variant t1/3. The size of the oil droplets determined by the time-resolved turbidity method is in good agreement with that of the TR-SAXS, highlighting the usefulness of the method in the size determination of oil-in-water microemulsions on an absolute scale.

The critical behavior of {water + AOT + decane} microemulsion with various molar ratios of water to AOT

To examine the critical behavior of the microemulsion, we have determined the coexistence curves for two ternary microemulsion systems of {water + sodium di(2-ethylhexyl) sulfosuccinate (AOT) + n-decane} with the molar ratios ω = (45.2 and 50.0) of water to AOT, respectively, by measuring refractive index at a constant pressure in the critical region. The critical exponent β and the critical amplitude B have been deduced from the coexistence curves. It was found that the values of β for both systems were consistent with the 3D-Ising exponent in a critical region. By increasing ω, i.e. the droplet size, the critical temperature and, to a lesser extent, the critical concentration decrease. The region of coexisting two phases was drastically reduced by an increase in the droplet size.

Evaluation of nanometer-scale droplets in a ternary o/w microemulsion using SAXS and 129Xe NMR

This study revealed a linear correlation between the nanometer-scale oil droplet sizes estimated using small angle X-ray scatterings (SAXS) and the 129Xe NMR chemical shift in an oil-in-water ternary microemulsion system comprising pentaethylene glycol mono- n-dodecyl ether, n-decane, and deuterium oxide. The absolute values of the droplet size estimated using 129Xe NMR show good agreement with those using SAXS. We also found that the results are consistent with a reported relation derived using small angle neutron scattering. The results suggest the validity of 129Xe NMR chemical shifts for investigation of colloidal systems to evaluate their internal structures’ characteristic sizes.

The critical phenomena of (water + AOT + decane) microemulsion with the molar ratio ( ω = 30.0) of water to AOT

The coexistence curves of a ternary microemulsion system of {water + sodium di(2-ethylhexyl) sulfosuccinate (AOT) + n-decane} with the molar ratio (30.0) of water to AOT have been determined by measurements of refractive index at constant pressure within about 8 K from the critical temperature T c. The critical exponent β and the critical amplitude B have been deduced from the coexistence curves. The experimental results have been analysed and compared with the system with molar ratio of 40.8 studied previously. It was found that the critical exponents β for both systems were consistent with the 3D-Ising value in a region sufficiently close to the critical temperature. The critical concentration was slightly affected by the molar ratio ω, but the critical temperature significantly was raised as the molar ratio ω was decreased. The volume fraction ϕ was the better choice of the concentration variable than the effective volume fraction ψ and the refractive index n used for constructing the order parameter for both systems.

Dependence on Oil Chain‐Length of the Curvature Elastic Properties of Nonionic Surfactant Films: Droplet Growth from Spheres to a Bicontinuous Network

Using NMR self‐diffusion and 2H‐NMR relaxation experiments, we have investigated growth of oil‐in‐water microemulsion droplets when spontaneous curvature is lowered, starting at emulsification failure boundary. We compare two ternary nonionic microemulsion systems, containing penta‐ethylene glycol dodecyl ether (C12E5), and decane or hexadecane, at same surfactant‐to‐oil ratio and approximately the same spontaneous curvature. Droplet growth in microemulsions appears in general to be only minor. Quantitative differences between the two systems indicate differences in the curvature elastic constants.

Structural Properties of Pure Simple Alcohols from Ethanol, Propanol, Butanol, Pentanol, to Hexanol: Comparing Monte Carlo Simulations with Experimental SAXS Data

The primary liquid alcohols from ethanol to 1-hexanol were studied utilizing the configurational-bias Monte Carlo (MC) simulations of the modeled alcohols (transferable potential for phase equilibria-united atom model) and the small-angle X-ray scattering (SAXS) method. A novel approach for calculating the scattering intensities from the theoretically obtained MC data by utilizing the Debye equation and their further validation with experimental results was introduced. This procedure is important, since the common problem of how to initially separate the intra- and intermolecular contributions to the scattering when comparing the calculated and experimental data was successfully avoided. Nevertheless, the intra- and intermolecular contributions to the scattering were able to be investigated directly from the MC results. The most pretentious task of the procedure was the suppression of the MC box background scattering, which was solved by utilizing the averaging of the scattering intensities over the different box sizes. This method of the scattering intensity calculations enabled us to make a theoretical analog to the well-known small-angle neutron scattering contrast matching experiment that, in our case, nicely revealed the origin of the two alcohol scattering peaks in the SAXS regime of the scattering curves (0.3 A(-1) < q < 3 A(-1)). For the example of butanol, the outer alcohol scattering peaks at approximately 1.40 A(-1) were unambiguously ascribed to the correlations between the alcohol hydrocarbon tails described by the gCH(x)CH(x)(r) pair correlation function. Similarly, the inner alcohol scattering peaks that shift from approximately 0.8 to approximately 0.4 A(-1) with an increasing alkyl chain length of the alcohol molecule are mainly the consequence of the O-O correlations. These findings were tested on pentanol/water mixtures and further applied to the results of the structural investigations on the binary and ternary microemulsion systems of the nonionic surfactant Brij 35 (Tomsic, et al. J. Phys. Chem. B 2004, 108, 7021; Tomsic, et al. J. Colloid Interface Sci. 2006, 294, 194), which were in fact the actual motivation for this present study.

Preparation of NiB nanoparticles in water-in-oil microemulsions and their catalysis during hydrogenation of carbonyl and olefinic groups

Abstract Surfactant-stabilized NiB catalysts (ME-NiB) were prepared using the chemical reduction method in the ternary microemulsion system of water/cetyl-trimethyl-ammonium bromide (CTAB)/ n -hexanol. The surfactant molecules could adsorb onto the surface of the formed particles, and acted as a protective agent to stabilize and restrict the growth of particles. The size of the nanoparticles was not fully determined by the size of the microemulsion droplets, which depended on the composition of the microemulsion system. Additionally, the particle sizes and the reactivities of the ME-NiB nanoparticles depended on the concentration of nickel salt, the amount and speed of addition of NaBH 4 and the temperature. The ME-NiB samples were characterized by X-ray diffraction (XRD) as an amorphous structure and by transmission electron microscopy (TEM) as having particle size distributions in the range 3–8 nm, which was much smaller than that of NiB (20–50 nm) prepared by the typical chemical reduction method. The ultrafine catalyst of ME-NiB was markedly more active than NiB in the hydrogenation of carbonyl and olefinic groups. A good yield of citronellal/citronellol was obtained from the selective hydrogenation of citral at a low temperature of 30 °C over the ME-NiB catalyst.

Pressure-dependence of the bending modulus of surfactant monolayers in ternary microemulsion systems observed by neutron spin echo

Pressure-dependence of dynamical fluctuations of surfactant monolayers of ternary microemulsion systems with an ionic surfactant and a non-ionic surfactant were investigated by neutron spin echo. The bending modulus of surfactant monolayers increased with increasing pressure both in the cases of the ionic surfactant and of the non-ionic surfactant. It is confirmed that the compression of hydrocarbon tails of surfactant is the main origin of pressure-induced phase transitions.

Pressure-induced hexagonal phase in a ternary microemulsion system composed of a nonionic surfactant, water, and oil

The pressure-induced phase transition in a microemulsion, consisting of pentaethylene glycol mono-n-dodecyl ether, water, and n-octane, was investigated by means of small-angle neutron scattering. A pressure-induced phase transition from a lamellar structure to a hexagonal structure was observed. The temperature-pressure phase boundary shows a positive slope with dTdP approximately 0.09 KMPa. The structure unit of the high-pressure hexagonal phase was an oil-in-water cylinder with the membrane thickness of 15.5 A, identical to the low-temperature hexagonal phase. Pressurizing was found to have the same effect by decreasing temperature. This behavior was satisfactorily explained with the pressure dependence of the spontaneous curvature of surfactant membranes. That is, the volume change of surfactant tails plays a dominant role in the structure change of the microemulsion with applying pressure.

Coexistence curves of critical nonaqueous microemulsions of (AOT + DMA + nonane) and (AOT + DMA + octane)

The coexistence curves of ( T, n), ( T, ϕ) and ( T, ψ) ( n, ϕ, ψ are the refractive index, the volume fraction, and the effective volume fraction, respectively) for two ternary nonaqueous microemulsion systems have been determined at constant pressure and a constant molar ratio ω of DMA to AOT. The critical exponent β and the critical amplitude B have been deduced, and the values of β were consistent with the theory of 3D-Ising in a region sufficiently close to the critical temperature. The results show that the coexistence curves have been successfully described by the Wegner equation and the expression for the diameter.

Critical behaviour of { water + n-nonane + sodium di(2-ethyl-1-hexyl)sulphosuccinate } microemulsions

Coexistence curves of ( T, n), ( T, ϕ), and ( T, Ψ), where n, ϕ, and Ψ are the refractive index, volume fraction and effective volume fraction ψ=ϕ/{ϕ+ [(1 −ϕ )ϕc/(1 −ϕc )]}, respectively, for ternary microemulsion systems of {water +n -nonane + sodium di(2-ethyl-1-hexyl)sulphosuccinate} have been determined at temperatures within 8.7 K above the critical temperature by measurements of refractive index at constant pressure and a constant molar ratio of water to sodium di(2-ethyl-1-hexyl)sulphosuccinate. The critical exponent β deduced from ( T,n ), ( T, ϕ), and ( T, Ψ) coexistence curves was found consistent with nonmonotonic crossover observed in all aqueous ionic solutions. The values of β deduced from the experimental data in the range of 1 K above Tcwere consistent with the universality class of three-dimensional Ising-like systems. The coexistence curves have been interpreted by a combination of the Wegner expansion and the rectilinear diameter. The present results indicate that the molar mass dependence of critical amplitudes, we proposed recently, is valid for microemulsion systems.

Phase diagram and physical properties of a waterless sodium bis(2-ethylhexylsulfosuccinate)- ethylbenzene-ethyleneglycol microemulsion: an insight into percolation.

Volumetric and transport studies have been carried out for the nonaqueous ternary microemulsion system containing sodium bis(2-ethylhexylsulfosuccinate) aerosol-OT (AOT), ethylbenzene (EB), and ethyleneglycol (EG). The results obtained for the conductivity sigma are presented over a wide range of volume fraction of dispersed phase phi and different molar concentration ratio omega=[EG]/[AOT]=2-10 at 30 degrees C and discussed in context of percolation theory. The variation of sigma with respect to temperature (T=10-60 degrees C) shows an increase in the conductance values but no percolation-type phenomenon is observed. The measurements of viscosity, density, and ultrasonic velocity have also been carried out to understand the behavior of this nonaqueous microemulsion system. The phase behavior of the microemulsion is sensitively dependent on the EG to AOT molar ratio. A simple structural model has been applied for the calculation of the various parameters, i.e., aggregation number (n), core radius (r(n)), and surface number density of the surfactant molecule at interface (alpha(s)).