Microemulsion alcohol free

Wu, B., Harwell, J. H., Sabatini, D. A., and Bailey, J. D. (1999). Alcohol-Free Diphenyloxide Disulfonate (DPDS) Middle Phase Microemulsion Systems, Journal of Surfactants and Detergents. 

Alcohol-Free Microemulsions. Three alcohol-free systems were prepared in order to determine their solubilization characteristics. Friberg (9) has suggested that a protic solvent (alcohol, amine, acid, etc.) is necessary for microemulsion formation, while... 

Ghosh O, Miller CA. Liquid crystalline and microemulsion phase behavior in alcohol-free aerosol-OT/oil/brine systems. J Phys Chem 1987 91 4528-4535. 

Sanz and Pope [17] have screened combinations of ethoxylated sulfonates and alkylaryl sulfonates for alcohol-free chemical flooding purposes. They observed difficulties in obtaining clean or gel-free microemulsions at the phase transition from Type II( —) to Type III, which means that surfactant retention and pore plugging may take place. Thus, it appears to be an advantage to stay in the two-phase region during the flood process. 

To illustrate the present theory, calculations were carried outfor a system consisting of an anionic surfactant, oil, water, alcohol, and electrolyte. Obviously, this model can be readily applied to simpler microemulsions free of alcohol, wherein the phase transitions are caused by varying the electrolyte concentration or the temperature. 

The standard free energy difference A//W in eq 3.1 is due to the transfer of one surfactant molecule and (gAi/gsd alcohol molecules from water and (goi/gsi) oil molecules from pure oil to the interfacial layer of the microemulsion droplet. Expressions for A/ ° are provided in section 7 of the paper. 

The equations developed in previous sections can be used to calculate the structural features of microemulsions, provided explicit expressions for the standard free energies of transfer of surfactant and alcohol molecules from their infinitely dilute states in water and of oil molecules from the pure oil phase to the interfacial layer of the microemulsion droplets are available. Such expressions are given below for spherical layers of O/W droplets and W/O droplets and also for flat layers. The difference in the standard state free energy consists of a number of contributions ... 

Partition constants report the equilibrium distribution of components in aggregated systems but do not represent the free energy of transfer of alcohols between aggregates and the bulk aqueous or oil phases, and their values need not be independent of solution composition, especially when the alcohol concentration in the aggregates or the bulk phase is high. However, alcohol distributions expressed as mass-action binding constants in aqueous three-component microemulsions [reaction (16)] and in W/O microemulsions [reaction (17)] are independent of alcohol concentration. 

Specific roles of the so-called co-surfactants (commonly, but not necessarily alcohols) have been examined by various workers [122, 126, 136] some points are discussed here. For example, a critical thermodynamic analysis in conjunction with experimentations led Eicke [ 136] to the conclusion that a co-surfactant should decrease the interfacial free energy under isothermal conditions, while causing an uptake of water into the microemulsion and extension of its domain. The anionic surfactant AOT assists the formation of large reverse microemulsion domains (high water uptake) in different ternary systems without help from a co-surfactant (Section 2.2), but cationic surfactants do generally need this fourth component. In spite of this, enhanced solubilization by the addition of (small quantities of) a co-surfactant has been observed by various workers in AOT systems. Eicke [136] used cyclohexane, benzene, carbon tetrachloride and nitrobenzene in the system AOT/ isooctane/water and found considerable water uptake (the fraction of the oil phase, i.e. isooctane was 0.8 or more). With increasing polarizability or polarity of the CO-surfactant, the water uptake decreased. 

Fig. 3.8. Organisation of a surfactant in an oil-in-water (0/W) colloidal emulsion. There also exist systems a little more complex than the simple surfactants (alcohol/surfactant mixtures) with the property that their co-adsorption at the O/W interface is energetically favoured (corresponding to a negative variation in free energy AG). In that case the system is thermodynamically stable and the dispersion forms spontaneously. The dispersed particles are extremely small (microemulsion) and the system remains stable indefinitely...

Significant research efforts have been devoted to the free-radical polymerization of hydrophobic monomers [eg, ST, methyl methacrylate (MMA), and butyl acrylate (BA)] in 0/W microemulsions. The anionic surfactant SDS in combination with a short-chain alcohol (eg, C5OH) as the cosurfactant is the most popular stabilization package. However, as more polymer forms with the progress of polymerization, the increase of free energy as a result of the conformational limitation and/or incompatibility between polymer and cosurfactant results in the instability or turbidity of microemulsion polymer (16). When a cationic surfactant. 

FIG. 1 Typical DSC thermograms of K-oleate-hexanol-dodecane-water microemul-sion samples. Surfactant/oil = 0.2 g/mL alcohol/oil = 0.4ml/mL water/(water + oil) = 0.222-0.4 g/g. Curve a, W/O microemulsion sample curve b, D2O/01I microemulsion sample. Endothermic peaks due to the fusion of DjO (277 K), free water (273 K), dodecane and interphasal water (263 K), bound water (233 K), and hexanol (220 K) were identified. (From Ref. 11.)... 

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