Solubilization binary solutions

One of the major goals of these many investigations of lipids is, of course, a better understanding of the in - vivo behavior of membranes. Beyond studies of binary lipid mixtures, as mentioned above, a further step which is necessary is the incorporation of proteins into the layers. In many respects, this increase in the complexity of the bilayer systems resembles that encountered in the use of synthetic surfactants in "real - world" situations, where blends, rather than single, surfactants are used. Surfactant blends in aqueous solutions are often further modified in use by the solubilization of oily organic compounds, as in the cases of detergency or cosmetic formulation. 

Winsor, P.A. (1968) Binary and multicomponent solutions of amphiphilic compounds. Solubilization and the formation, structure and theoretical significance of liquid crystalline solutions. Chem. Rev., 68, 1. 

Winsor, P. A., Chem. Rev. (1968) 68, 1-40, "Binary and Multicomponent Solutions of Amphiphilic Compounds. Solubilization and the Formation, Structure, and Theoretical Significance of Liquid Crystalline Solutions."... 

Systems Containing More Than Two Components. As in binary systems, the behavior of systems containing more than two components can be understood on the basis of intermolecular forces and solubility parameters. Water and tetrachloromethane have widely differing solubility and hydrogen bond parameters, and are therefore immiscible. Added acetone dissolves partly in the aqueous phase due to hydrogen bond formation, and partly in the tetrachloromethane phase due to dispersion and induction forces. Twice as much acetone dissolves in the aqueous phase as in tetrachloromethane. On increasing the acetone concentration a homogeneous solution is obtained. The added solvent thus acts as a solubilizer for the two immiscible solvents. 

This chapter will focus on a simpler version of such a spatially coarse-grained model applied to micellization in binary (surfactant-solvent) systems and to phase behavior in three-component solutions containing an oil phase. The use of simulations for studying solubilization and phase separation in surfactant-oil-water systems is relatively recent, and only limited results are available in the literature. We consider a few major studies from among those available. Although the bulk of this chapter focuses on lattice Monte Carlo (MC) simulations, we begin with some observations based on molecular dynamics (MD) simulations of micellization. In the case of MC simulations, studies of both micellization and microemulsion phase behavior are presented. (Readers unfamiliar with details of Monte Carlo and molecular dynamics methods may consult standard references such as Refs. 5-8 for background.)... 

Micellization, which forms a major focus of this chapter, is the simplest class of phenomena accessible through simulations and, perhaps arguably, is the first step that needs to be examined before embarking on more complex problems. Both micellization [30,31] and micellar phase behavior [32] have been studied by Care and coworkers for a binary surfactant-solvent system using simple lattice models of the type we discuss here. The recent work of Talsania et al. [33] includes a preliminary examination of micellar solubilization, in addition to micellization in surfactant solutions. The latter is the first attempt to examine solubilization (i.e., encapsulation) at low solute (i.e., oil) concentration in a systematic manner. 

Ethers are solvents of low to moderate polarity. They are proton acceptors and in general have dipole moments much lower than those of alcohols. Ethers readily solubilize nonpolar to moderately polar solutes. Ethers also run the gamut of solubility with water. THF and dioxane are miscible, whereas ethyl ether and methyl r-butyl ether (MrBE) are immiscible. THF and dioxane are therefore commonly used as the organic component in a binary solvent for RP separations. Ethyl ether and MrBE are used as the polar constituents in NP separations or in ternary aqueous solvents (with a mutually miscible third component such as IPA) for RP separations. 

A common problem in the evaluation of binary and ternary systems to which a solute has been added is the basic distinction between the mean area per molecule and the partial molecular surface. When areas per molecules are measured, the link between total area and molar fraction may be highly nonlinear, in particular for the case of solutes denominated as cosurfactants which are solubilized in the palisade layer. The partial molar area is the increase of surface per surfactant due to the addition of a solute at a constant density of surfactant, while the area is the observed average. This problem has been discussed in detail by Boden et al. (5). 

The classical treatment of the internal oxidation of binary alloys was first developed by Wagner (1959) and reviewed later by others (Rapp, 1965 S yisher, 1971 Stott and Wood, 1988 Douglass, 1995). Consider a binary, single-phase alloy A-B in which B is the solute and more reactive element. The necessary and sufficient criteria for the internal precipitation of BX, where X is the oxidant, are that the amount of B in the alloy must be below the critical value necessary for the transition from internal to external BX formation, and that the solubil-... 

Lawrence [10-12] extended this work, suggesting that the increased solubility of a solubilizate in a surfactant solution was due to some form of attachment of the solubilizate to the exterior of the micelle or solution in it. He also pointed out a difference in behaviour when polar and non-polar molecules were solubilized, and the increased solubility of the soap itself with the addition of a polar solubilizate. Hartley [13] made the further contribution that solubilization occurred only above the CMC above this, the amount of substance solubilized increased with soap concentration. This work in turn evolved a widely used technique for determining the CMC, but great care must be taken in evaluating results from this technique, as it involves the use of ternary systems to investigate a binary one. 

As shown above, it has been known for some time that the solubility of polyelectrolytes in aqueous media can be influenced by the electrochemical switching of the counterions. However, this principle has only recently been applied to trigger electrochemically built-up micellar aggregates from unimolecular solutions by adjusting the solubility of one part of a binary block-like copolymer [235]. Hereby, the electrolysis of ferrocyanide to ferricyanide led to the formation of vesicles (polymersomes). In contrast to real film formation, the solubilizing part, poly (ethylene oxide) (PEO), prevented film deposition on the electrode. Instead, bilayer film formation in bulk solution was favored under vesicle build-up with an insoluble polyelectrolyte complex as the vesicle wall, sandwiched between a well-hydrated PEO brush. 

Treiner, C. The thermodynamics of micellar solubilization of neutral solutes in aqueous binary surfactant systems. Chem. Soc. Rev. 1994, 25(5), 349-356. 

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