Water pseudo-binary phase diagram

FIGURE 7.10 Pseudo-binary phase diagram of the water, HNO3/DMDBTDMA, dodecane system to identify the third-phase limit. Experimental points (circles) and theory (lines) obtained from Baxter sticky hard-sphere approach. The theoretical line is obtained with the experimental determination of the linear variation of the stickiness parameter tt1 versus [HN03]/[DMDBTDMA]. The different lines illustrate the impact of the error in this T-1 experimental linear law. (From C. Erlinger, L. Belloni, T. Zemb, and C. Madic, Langmuir, 15 2290-2300, 1999. With permission). 

Another useful pseudo-binary phase diagram is found upon fixing the surfactant concentration (y constant), and varying the ratio of oil to water (vary a) as a function of temperature. For surfactant concentrations greater than y, a one-phase channel is observed in the phase diagram, which spans all oil to water ratios (Figure 4.7). In the example shown in this figure, the... 

Figure 9.14. Pseudo-binary phase diagram of the water-oil-C/Ey system at equal water-to-oil volume ratios, representing the so-called fish-tail . This temperature-surfactant content T-y) representation is used to determine the temperature of the zero spontaneous curvature and the minimum amount of surfactant needed to include equal volumes of oil and water in a single-phase microemulsion...

Figure 9.15. Pseudo-binary phase diagram of the water-oil(cyclohexane - - lindane)-C6E5 system for different initial weight compositions of lindane in the oil , 0 x, 4 , 10 A, 15%. The arrow indicates the variation of the fish-tail with the increasing content of lindane in the oil, while the temperature T of the zero spontaneous curvature is given by the ordinate of the fish-tail...

To evaluate the phase equilibria of binary gas mixtures in contact with water, consider phase diagrams showing pressure versus pseudo-binary hydrocarbon composition. Water is present in excess throughout the phase diagrams and so the compositions of each phase is relative only to the hydrocarbon content. This type of analysis is particularly useful for hydrate phase equilibria since the distribution of the guests is of most importance. This section will discuss one diagram of each binary hydrate mixture of methane, ethane, and propane at a temperature of 277.6 K. 

Furfiier evidence fiiat supports these calculations derives from studies of the ternary mixtures of the cationic double-chain surfactant DDAB (didodecyl dimethyl ammonium bromide), cyclohexane and water. Within the cubic mesophase region of fiiis surfactant-water-oil mixtiure, all the cyclohexane is adsorbed between the surfactant chains, so that the system is a pseudo-binary one, for which our theoretical analysis ought to hold. (The effective surfactant parameter for fliis surfactant in the presence of cyclohexane is slightly larger tiian unity.) Close scrutiny of the cubic phase region within this ternary phase diagram has revealed the presence of at least one - and... 

For a large variety of amphiphilic compoimds cubic phases are a particular class of surfactant systems normally observed in the more concentrated region of the phase diagram [53]. Such phases may occur in binary systems (surfactant and water) as well as in ternary or pseudo ternary systems, where usually a hydrocarbon is the third component. In addition they may contain a long alcohol chain as a fourth component (cosurfactant). Such a composition reminds one of that of microemulsions and for that reason they are also called microemulsion gels [54]. However, the denomination cubic phase is insofar more instructive since it relates directly to the structure of the corresponding systems. 

Systematic studies of the phase behavior of lipid-surfactant systems have been performed particularly on mixtures of surfactants of the Ci2EOn type and phosphatidylcholines with different chain lengths and saturation [109-113]. The phase diagrams of these pseudo-binary mixtures in excess water are complicated and become even more so when the water content is varied. 

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