Properties and structure of three-component ionic microemulsions (original) (raw)
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Structural studies of ionic liquid-modified microemulsions
Journal of Colloid and Interface Science, 2009
This work is focused on the influence of an ionic liquid (IL), i.e. ethyl-methylimidazolium hexylsulfate, on the spontaneous formation of microemulsions with ionic surfactants. The influence of the ionic liquid on structure formation in the optically clear phase region in water/toluene/pentanol mixtures in presence of the cationic surfactant CTAB was studied in more detail. The results show a significant increase of the transparent phase region by adding the ionic liquid. Conductometric investigations demonstrate that adding the ionic liquid can drastically reduce the droplet-droplet interactions in the L 2 phase. 1 H nuclear magnetic resonance ( 1 H NMR) diffusion coefficient measurements in combination with dynamic light scattering measurements clearly show that inverse microemulsion droplets still exist, but the droplet size is decreased to 2 nm. A more detailed characterisation of the isotropic phase channel by means of conductivity measurements, dynamic light scattering (DLS), 1 H NMR and cryo-scanning electron microscopy (SEM), allows the identification of a bicontinuous sponge phase between the L 1 and L 2 phase. When the poly(ethyleneimine) is added, the isotropic phase range is reduced drastically, but the inverse microemulsion range still exists.
Ionic liquid microemulsions and their technological applications
Ionic liquids are receiving much attention as environmentally benign media for reactions, separations, and multidisciplinary chemistry, due to their unique physicochemical properties which include non-volatility, high stability, high ionic conductivity, wide electrochemical window and easy recyclability. We summarize herein microemulsion formulations and applications where ionic liquids are used as oil substitutes, water substitutes, co-surfactants (additives) and surfactants.
Hypothesis: Although several studies on water-in-hydrocarbon oil microemulsions stabilized by anionic surfactant are available in literature, such study on oils possess comparable molar volumes with different chemical architectures and physicochemical properties, herein R-(+)-limonene (LIM) and isobutyl benzene (IBB) derived microemulsions in absence or presence of ionic liquid (IL) warrants uniqueness of this report. Experiments: The present study delineates interfacial composition and thermodynamics properties of sodium dodecylsulfate, SDS/1-pentanol/LIM or IBB/water microemulsions in absence or presence of IL, 1-butyl-3-methylimidazolium chloride (bmimCl) as additive by the dilution method. Further, precise characterization of these systems is accomplished by conductivity and DLS studies as function of ω, [bmimCl] and temperature, which provide an insight into unique features of the oil/water interface. Finally, the influence ofdistinctive features ofoils and the states ofwater organization in nanopool ofthese microemulsions have been explored from steady state fluorescence emission, fluorescence anisotropy and FTIR measurements. Findings: bmimCl containing microemulsions are more spontaneous than aqueous microemulsions. Addition of bmimCl yields smaller droplets compared to aqueous system. Fluorescence measurements reveal penetration of oil molecules in the surfactant palisade layer vis-a-vis interfacial micropolarity and their consequential effects in microenvironment of microemulsions in absence or presence of bmimCl, using suitable molecular probes. Apart from reciprocal variation in free and bound water with increasing water content, results exhibit mild variation in interfacial water (which is basically trapped water in the hydrophobic tail region of surfactant) by changing oil continuum. Finally, correlation of the results in terms of evaluated physicochemical and thermodynamic parameters has been presented.
Fluid Phase Equilibria, 2014
The present study is focused on the determination of the solubilization capacity and conductance behavior of mixed microemulsions [AOT/Brij-56 or Brij-58 or Brij-76 or TX-100 or Tween-80/Hp or Dc or IPM/water] in presence of ionic liquids (ILs) of different chemical structures and physicochemical properties [viz. bmimCl, hmimCl, bmimBF 4 and BzmimCl] at different compositions (X nonionic = 0, 0.1) at fixed surfactant concentration and temperature. Synergism in solubilization capacity has been evidenced in presence of ILs. All these systems exhibit volumeinduced percolation of conductance. The maximum solubilization capacity (ω 0,max), [IL] max (concentration of ILs at which synergism occurs) and volume-induced percolation threshold (ω p) have been found to influence by alkyl side-chain length, anion and polarity of ILs, and polar head group, hydrophobic moiety and content of nonionic surfactant and type of oils. Different solubilization sites of bmimCl and hmimCl have been proposed. ILs have been found to be more efficient additives than NaCl in respect of enhancing ω 0,max with less [IL] max and reducing ω p. The microstructure of AOT and AOT/Brij-56 systems at different X nonionic (= 0, 0.1) has been determined by DLS and FTIR measurements in absence and presence of ILs. Droplet diameter (d h) decreases and relative population of bound water increases with increase in [IL]. An attempt has been made to correlate the solubilization capacity in presence of ILs with percolation of conductance vis-à-vis droplet dimensions and the states of confined water to underline mechanism of solubilization phenomenon in these systems.
Phase behavior and microstructure of sugar surfactant-ionic liquid microemulsions
Journal of Dispersion Science and Technology, 2020
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, c. 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/nonpolar 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 b-D-maltoside, and ndodecyl b-D-maltoside, to solubilize oil (hydrophobic ionic liquid) and water, i.e., X 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.
Model microemulsions containing vegetable oils 2. Ionic surfactant systems
1989
aKarishamns AB, Division R&D, S-374 82 Karlshamn, Sweden and blnstitute for Surface Chemistry, S-114 86 Stockholm, Sweden Nonionic microemulsions containing triglycerides and fatty acid esters as lipophilic components have been studied. The phase inversion temperature (PIT) of the systems was determined by a conductometric method. Partial phase diagrams were constructed in the phase inversion temperature range. Water solubilization capacity of the nonionic surfactant systems studied was dependent on surfactant and oil types in analogy to ordinary hydrocarbon systems. The PIT:s increased with increased molecular weight for both esters and triglycerides.
Studies on formation and percolation in ionic liquids/TX-100/water microemulsions
Journal of Molecular Liquids, 2014
] 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 H 2 O/Triton X-100/[BMIM] [PF 6 ]. 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.
Nonaqueous microemulsion-containing ionic liquid [bmim][PF6] as polar microenvironment
Colloid and Polymer Science, 2005
The phase behavior of toluene/Triton X-100 (TX-100)/1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]) was studied. It was demonstrated that the single-phase microemulsion area covered about 75% of the phase diagram at 25°C. Electrical conductivities of the system with different w ([bmim][PF6]-to-TX-100 molar ratio) values were determined, and the results were used to locate the sub-regions of the single-phase microemulsion. The results showed that a transform from [bmim][PF6]in-oil ([bmim][PF6]/O) microstructure via a bicontinuous region to an oil-in-[bmim][PF6] (O/[bmim][PF6]) microstructure occurred with the increase of F (weight fraction of TX-100 and [bmim][PF6] in the system). The aggregate size of the reverse microemulsions of [bmim][PF6]/O was determined using small-angle X-ray scattering. The results showed that the size of the reverse microemulsions depended markedly on the w values.
Nonaqueous Microemulsions Based on N , N ′-Alkylimidazolium Alkylsulfate Ionic Liquids
Langmuir, 2013
The ternary system composed of the ionic liquid surfactant (IL-S) 1-butyl-3methylimidazolium dodecylsulfate ([Bmim][DodSO 4 ]), the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO 4 ]) and toluene has been investigated. Three major mechanisms guiding the structure of the isotropic phase were identified by means of conductometric experiments, which have been correlated to the presence of oil-in-IL, bicontinuous, and IL-in-oil microemulsions. IL-S forms micelles in toluene, which swell by adding RTIL as to be shown by Dynamic Light Scattering (DLS) and Small Angle X-ray Scattering (SAXS) experiments. Therefore, it is possible to form water-free IL-in-oil reverse microemulsions ≤ 10 nm in size as a new type of nanoreactor.