Amphiphile-oil-water systems

Fig. 1. Phase diagram of an amphiphile—oil—water system that forms a middle-phase microemulsion, definition of microemulsion, and illustration of the...

Amphiphile-oil-water system, temperature of, 16 424-426 Amphiphiles, 16 420 Amphiphile strength, 6 424 Amphiphilic chemicals, 17 56 Amphiphilic copolymers, 20 482 behavior of, 20 483 well-defined, 20 485-490 Amphiphilic molecules, 15 99-101 Amphiphilic plasticizers, 14 480 Amphiphilic polymer blend, 23 720 Amphiphilic polymers statistical, 20 484-490 stimuli-responsive, 20 482-483 Ampholytes, 9 746-747 Amphoteric cyclocopolymers, water-soluble, 23 721 Amphoteric starches, 4 722 Amphoteric (zwitterionic) surfactants, 24 148... 

Historically, however, it has been much more common for experimentalists to introduce a new variable into Figure 1, changing either the temperature of one or more samples of fixed composition, or the electrolyte concentration in a series of samples of fixed amphiphile—oil—water ratio. The former constitutes a temperature scan the latter experiment is widely known as a salinity scan. When the temperature of an amphiphile—oil—water system is varied, the phase diagram can be plotted as a triangular prism (because temperature is an intensive or field variable). When a fourth component (eg, NaCl) is added at constant temperature, tetrahedral coordinates, are appropriate (conjugate phases have different salinities, and the planes of different tietriangles are no longer parallel). 

Bourrel, M., Salager, J.L., Lipow, A.M., Wade, W.H. and Schechter, R.S. (1978) Properties of amphiphile/oil/water systems at an optimum formulation for phase behavior. SPE 7450 Presented at the 53rd Annual Fall Technical Conference and Exhibition of the SPE ofAIME, Houston, TX, October 1-3. 

JL Salager. Phase behavior of amphiphile-oil-water systems related to the butterfly catastrophe. J Colloid Interface Sci 105 21—26, 1985. 

Figure 16.3 also shows the phase diagrams of a nonionic amphiphile-oil-water system at TT c, respectively. Because of the relative densities of the phases, for Tupper-phase microemulsion in equilibrium with an aqueous phase, whereas for T>Tuc the system may be said to contain a lower-phase microemulsion in equilibrium with an oleic phase. However, if the existence of middle-phase microemulsions at intermediate temperatures is unknown, the respective phase pairs are likely to be called simply oil and water. 

Winsor [30] studied the phase behavior of amphiphile-oil-water systems as a function of the nature of the different components that make up the ternary system. By varying the nature of the different components and their respective proportions, he constructed ternary diagrams and was able to determine the different types of phase equilibria and map typical situations. The amphiphile may be a surfactant, although the cases reported by Wmsor are attained with a mixture of surfactant and cosurfactant with similar affinities for the oil and water phases. 

Fig. 5. Lower and upper critical tielines in a quaternary system at different temperatures and a plot of the critical end point salinities vs temperature, illustrating lower critical endline, upper critical endline, optimal line, and tricritical poiat for four-dimensional amphiphile—oil—water—electrolyte-temperature...

More recently suggested models for bulk systems treat oil, water and amphiphiles on equal footing and place them all on lattice sites. They are thus basically lattice models for ternary fluids, which are generalized to capture the essential properties of the amphiphiles. Oil, water, and amphiphiles are represented by Ising spins 5 = -1,0 and +1. If one considers all possible nearest-neighbor interactions between these three types of particle, one obtains a total number of three independent interaction parameters, and... 

Polarized light microscopy is a simple technique to learn and use, readily available, and of great value to differentiate between various anisotropic LC systems. It is also of value to formulation scientists investigating amphiphile-oil-water mixtures with emphasis on colloidal systems in general and MEs in particular. This is mainly due to the fact that many LC systems may appear transparent to the naked eye and can be easily misinterpreted as isotropic ME systems. Thus it becomes essential when investigating systems of amphiphile-oil-water to confirm findings based on visual appearance with polarized light microscopic examination. 

Ringard-Lefebvre, C., Bochot, A., Mcmigoglu, E., Charon, D., Duchene, D., and Baszkin, A. (2002), Effect of spread amphiphilic P-cyclodextrins on interfacial properties of the oil/water system, Coll. Surf. B Biointerf, 25,109-117. 

Alcohols, at least those of short chain length, have moieties that are neither extremely hydrophilic, nor extremely hydrophobic, and partition in a complex way between oil emd water, or between the oil-like interior of a micelle or membrane, and water. This property, together with their small head-group area, enables them to be used with siirfactant-water, or surfactant-oil-water systems to produce a rich diversity of microstructured solutions through changing curvature of the interface, as does cholesterol, for the same reasons. The self-assembly of biological aggregates is further complicated by the presence of amphiphilic proteins. 

Anton, R.E. et ah. Surfactant-oil-water systems near the affinity inversion. IX Optimum formulation and phase behavior of mixed anionic-cationic systems, J. Dispersion Sci. Technol., 14, 401, 1993. Kahlweit, M. et ah. General patterns of phase behavior of mixtures of water, nonpolar solvent, amphiphiles, and electrolytes, 1,2, Langmuir, 4, 499, 1988 5, 305, 1989. 

All these simulations refer to the Ising model on the simple cubic lattice. Of course, also more comphcated lattices have been studied, and Fig. 2 shows a comparison of a hep simulation with solid helium. Again model and reality agree nicely. The Ising model has also been used to study oil-water systems where amphiphilic molecules may form membranes, micelles, and vesicles [15]. 

FIG. 22 Oil-water interfacial tensions 70 (°) and plateau values of the interfacial tension ( ) for CioGi in oil-water systems with increasing amphiphilicity of the oil [64]. 

Most characteristics of amphiphilic systems are associated with the alteration of the interfacial stnicture by the amphiphile. Addition of amphiphiles might reduce the free-energy costs by a dramatic factor (up to 10 dyn cm in the oil/water/amphiphile mixture). Adding amphiphiles to a solution or a mixture often leads to the fomiation of a microenuilsion or spatially ordered phases. In many aspects these systems can be conceived as an assembly of internal interfaces. The interfaces might separate oil and water in a ternary mixture or they might be amphiphilic bilayers in... 

FIG. 1 Self-assembled structures in amphiphilic systems micellar structures (a) and (b) exist in aqueous solution as well as in ternary oil/water/amphiphile mixtures. In the latter case, they are swollen by the oil on the hydrophobic (tail) side. Monolayers (c) separate water from oil domains in ternary systems. Lipids in water tend to form bilayers (d) rather than micelles, since their hydrophobic block (two chains) is so compact and bulky, compared to the head group, that they cannot easily pack into a sphere [4]. At small concentrations, bilayers often close up to form vesicles (e). Some surfactants also form cyhndrical (wormlike) micelles (not shown). 

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