One-phase Microemulsion Region Research Articles

Thermally stable microemulsions comprising imidazolium based surface active ionic liquids, non-polar ionic liquid and ethylene glycol as polar phase

Ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C2mim] [Tf2N], as a non-polar phase in conjunction with polar ethylene glycol (EG) forms microemulsions stabilized by surface active ionic liquids (SAILs), N-methyl-N-alkylimidazolium chlorides, [Cnmim] [Cl], where n = 8, 12 and 16 in conjunction with decanol as co-surfactant. The phase behaviour of the ternary systems has been investigated and three regions of microemulsions – polar-in-ionic liquid, bicontinuous and ionic liquid-in-polar, have been identified using electrical conductivity measurements. The effect of alkyl chain length on the phase behavior has been discussed in detail. The one-phase microemulsion region is found to decrease with the increase in the alkyl chain length of the SAILs. The microstructural characteristics have been investigated by using FTIR and NMR spectroscopy. The micropolarity of reverse micelles present in the microemulsions has been investigated using UV–Vis spectroscopy employing methyl orange as a polarity probe. The dynamics of solvent relaxation in microemulsions have been investigated by steady-state and time-resolved fluorescence spectroscopy using coumarin 153 (C-153) as fluorescence probe at different compositions of microemulsions. The dynamic light scattering measurements (DLS) reveals the expansion of reverse micelles formed by [Cnmim][Cl] in non polar [C2mim] [Tf2N] upon the addition of polar component. Interestingly, the microemulsions have been found to be thermally stable in a wide temperature range as revealed from temperature dependence UV–Vis, fluorescence and DLS measurements.

Formulation of Microemulsions Based on Sugar Surfactant as an Alternative Fuel

Microemulsion systems that serve as water in diesel fuel were formulated using minimum amount of sucrose laurate at 25°C. Comparative experiments were also conducted using n-heptane. It was found that in order to formulate diesel and microemulsions a cosurfactant should be added. Alcohols such as 1-butanol,1-pentanol, 1-hexanol, and 1-heptanol served as cosurfactants. The area of the one-phase microemulsion region varies depending on the cosurfactant structure and composition. A continuous microemulsion region was observed with 1-butanol and 1-pentanol. Water solubilization capacity and thermodynamics as a function of alcohol chain length was determined.

Phase Behavior of Pseudo-Ternary Gemini Surfactant + 1-Hexanol/Oil/Water Systems

Temperature dependent phase behavior of pseudo-ternary Gemini surfactant + 1-hexanol (1 : 5 molar ratios)/oil/water systems is reported from 0°C to 65°C. The influence of nature of hydrocarbon oil and type of electrolytes (weak as well as strong) has been investigated on the temperature induced phase behavior of the ternary system. At surfactant concentration,Φs=40%, a “nose-shaped” microemulsion region is observed. Below one-phase microemulsion region,Lαphase appears. The presence of NaCl decreases the domain size of1Φmicellar region whereas oxalic acid first decreases the domain belowΦw<18and then increases aboveΦw>18in the lower boundary of the phase diagram. The critical weight fraction of waterΦwcridecreases in presence of both electrolytes. However,Φwmaxincreases in presence of oxalic acid and remains constant in presence of NaCl as compared to salt-free system. Furthermore, when cyclohexane was replaced by a longer straight chain hydrocarbon, dodecane, the domain of the one-phase microemulsion region is tremendously increased.

Temperature Dependent Phase Behavior of Pseudo-Ternary Thiourea X-100 Surfactant +1-Hexanol/Oil/Water Systems

Temperature dependent phase behavior of Pseudo-ternary Thiourea X-100 + 1-hexanol (1:5 molar ratios)/oil/water systems is reported. The influence of nature of hydrocarbon oil and type of electrolytes (weak as well as strong) has been investigated on the temperature induced phase behavior of the ternary system. At surfactant concentration, Φs = 40%, a “nose shaped” microemulsion region is observed. Below one-phase microemulsion region, Lα phase appears. The presence of NaCl decreases the domain size of 1Φ micellar region whereas oxalic acid first decreases the domain below Φw 18 in the lower boundry of the phase diagram. The critical weight fraction of water, Φwcri decreases in presence of both electrolytes. However, Φwmax increases in presence of oxalic acid and remains constant in presence of NaCl as compared to salt free system. Furthermore, when cyclohexane was replaced by a longer straight chain hydrocarbon, dodecane, the domain of the one-phase microemulsion region is tremendously increased.

The Aerosol OT + n-Butanol + n-Heptane + Water System: Phase Behavior, Structure Characterization, and Application to Pt70Fe30 Nanoparticle Synthesis

A phase diagram of the pseudo-ternary Aerosol OT (AOT)+n-butanol/n-heptane/water system, at a mass ratio of AOT/n-butanol=2, is presented. Conductivity measurements showed that within the vast one-phase microemulsion region observed, the structural transition from water-in-oil to oil-in-water microemulsion occurs continuously without phase separation. This pseudo-ternary system was applied to the synthesis of carbon-supported Pt70Fe30 nanoparticles, and it was found that nanoparticles prepared in microemulsions containing n-butanol have more Fe than those prepared in ternary microemulsions of AOT/n-heptane/water under similar conditions. It was verified that introducing n-butanol as a cosurfactant into the AOT/n-heptane/water system lead to complete reduction of the Fe ions that allowed obtaining alloyed PtFe nanoparticles with the desired composition, without the need of preparing functionalized surfactants and/or the use of inert atmosphere.

Cosurfactant effects on the polymerization of vinyl acetate in anionic microemulsion media

The polymerization of vinyl acetate at 60 °C in microemulsions stabilized with the anionic surfactant, Aerosol OT, with or without cosurfactant ( n-butanol) is examined. Partial phase diagrams at 60 °C show that the addition of n-butanol enhances the one-phase microemulsion region. Results indicate that the reaction rate is not affected by the presence of the alcohol. However, average molar masses are smaller although particles are bigger throughout the reaction compared to those values obtained in the absence of n-butanol. An explanation for these results is presented.

Investigation of structure and structural transition in microemulsion systems of sodium dodecyl sulfonate+n-heptane+n-butanol+water by cyclic voltammetric and electrical conductivity measurements

Abstract A phase diagram of the pseudoternary C 12 H 25 SO 3 Na+ n -C 4 H 9 OH+ n -C 7 H 16 +H 2 O system at k m = W (C 4 H 9 OH)/ W (C 12 H 25 SO 3 Na)=2 is presented and a continuous transparent one-phase microemulsion channel is obtained. An investigation of the structural transition in this one-phase microemulsion region is carried out by cyclic voltammetry and conductivity techniques. Both cyclic voltammetric and conductivity measurements show that the structural transition from a water in oil microemulsion into an oil-in-water microemulsion happens completely continuously without any phase separation, and it takes place in two stages: with increasing water content, first, an oil continuous microemulsion transforms into a bicontinuous structure at roughly 45% (wet%) water content, and then at roughly 65% water content a bicontinuous microemulsion turns into a water continuous structure.

A model for the temperature-dependent interactions in uncharged droplet microemulsions

Microemulsions consisting of uncharged droplets generally behave as hard spheres at the solubilisation phase boundary (SPB) where the actual droplet size is close to the preferred droplet size. As the temperature is changed to move inside the one-phase microemulsion region, experimental data suggest that the droplets may either grow or cluster together due to increasing interdroplet attraction. We present a model in which it is assumed that droplet growth is absent and that the temperature dependence of the interdroplet interactions arises primarily from the energy associated with bending the stabilising surfactant monolayer. At temperatures close to the SPB, the actual curvature of the monolayer coating the droplets is close to its preferred value and the energy required to deform the interface is high, with the result that the droplets behave as hard spheres. Away from the SPB, where the actual monolayer curvature becomes higher than the preferred value, the energy required for deformation decreases and the droplets behave as ‘soft’ spheres. This results in an apparent increase in attractive interactions between the droplets. The model shows reasonable agreement with experimental turbidity data for uncharged microemulsions.

Phase Diagrams and Microstructure of Ionic Microemulsion Systems Containing Various Monoalkyl Poly (oxyalkylene) Ethers

Partial phase diagrams and microstructures were investigated in a one-phase microemulsion region of sodium oleate/monoalkyl poly (oxyalkylene) ethers/water ternary systems by conductivity, freezefracture electron microscopy and pulsed field gradient spin-echo (PGSE) NMR measurements. The influence of n-decane and glycerol trioleate on the ternary phase diagrams was also examined. Monomethyl, ethyl and butyl poly (oxyethylene) ethers and monobutyl ethers having both ethylene oxide (EO) and propylene oxide (PO) groups with different alkylene oxide chain length were used for this purpose. Although similar one phase microemulsion regions appeared in the monobutyl poly (oxyethylene) ether ternary systems, the microemulsion regions shrunk on increasing EO chain length by adding n-decane and glycerol trioleate. The introduction of PO groups at the terminal position of ethers had a spreading effect on the one phase region even in quaternary systems. Transition from water-in-oil to oil-in-water microemulsions through bicontinuous structures was found to occur with increase in water content.