Multiphase region

In Figure 1, the pairs (or triad) of phases that form ia the various multiphase regions of the diagram are illustrated by the corresponding test-tube samples. Except ia rare cases, the densities of oleic phases are less than the densities of conjugate microemulsions and the densities of microemulsions are less than the densities of conjugate aqueous phases. Thus, for samples whose compositions He within the oleic phase-microemulsion biaodal, the upper phase (ie, layer) is an oleic phase and the lower layer is a microemulsion. For compositions within the aqueous phase-microemulsion biaodal, the upper layer is a microemulsion and the lower layer is an aqueous phase. When a sample forms two layers, but the amphiphile concentration is too low for formation of a middle phase, neither layer is a microemulsion. Instead the upper layer is an oleic phase ("oil") and the lower layer is an aqueous phase ("water"). 

The composition points, the tie-lines and the phase envelope showing the multiphase regions were then plotted on the ternary diagram. Micellar solutions were selected... 

Fig. 15.4 Schematic ternary-phase diagram of an oU-water-surfactant microemulsion system consisting of various associated microstructures. A, normal miceUes or O/W microemulsions B, reverse micelles or W/O microemulsions C, concentrated microemulsion domain D, liquid-crystal or gel phase. Shaded areas represent multiphase regions.

In Figure I. the pairs (or triad 1 of phases that form in the various multiphase regions of the diagram are illustrated by the corresponding... 

The isotherm at 534° C. has a very sharp inflection, followed by an almost vertical portion, as the multiphase region is tranversed. The second inflection in... 

The 802° C. isotherm differs slightly from the others, in that the inflections at low hydrogen absorptions are not very pronounced. However, when the data are plotted on the phase diagram, a narrow multiphase region appears. Extrapolation indicates that above 875° C. this multiphase region would not exist. The remainder of the isotherm is the same as the others. 

Of the five different multiphase regions depicted in Figure 3, four were observed in our experiments. Phase compositions corresponding to the L1L2L3G equilibrium quadrilateral were measured at 40 C and 7.8 MPa. Phase compositions for L1L2L3 equilibrium were measured at 40 C and 8.4 MPa. Observations of L1L3G equilibrium were made at 40 C and 7.9 MPa, but phase... 

Table I. Boundaries of multiphase regions for the water-carbon dioxide-isopropanol system...

Ideally, the injected micellar solutions will be miscible with the fluids that they are in contact with in the reservoir and can thus miscibly displace those fluids. In turn, the micellar solutions may be miscibly displaced by water. Highest oil recovery will result if the injected micellar solution is miscible with the reservoir oil. If there are no interfaces, interfacial forces that trap oil will be absent. Injection of compositions lying above the multiphase boundary initially solubilizes both water and oil and displaces them in a misciblelike manner. However as injection of the micellar solution progresses, mixing occurs with the oil and brine at the flood front, and surfactant losses occur because of adsorption on the reservoir rock. These compositional changes move the system into the multiphase region. The ability of... 

The maximum in catalytic activity observed for the multiphase region of the phase diagram necessarily arises from interactions between the separate phases. The bismuth rich and cerium rich solid solutions can readily form coherent interfaces at the phase boundaries due to the structural similarities between the two phases which can permit epitaxial nucleation and growth. A good lattice match exists between the [010] faces of the compounds, this match is displayed in Figure 6. We have also shown that regions of an [010] face of a Ce doped bismuth molybdate crystal resembles cerium molybdate compos tionally. This means that the interface between the two compounds need not have sharp composition gradients. It is structurally possible for the Bi-rich phase to possess a metal stiochiometry at the surface that matches that of the Ce-rich phase. 

The general pattern of microemulsion phase behavior described above is seen when the amounts of water and hydrocarbon present are comparable. However, a hydrocarbon-free mixture of surfactant and water (or brine) near optimal conditions is typically not a simple micellar solution but either the lamellar liquid crystalline phase or a dispersion of this phase in water. Starting with such a mixture and adding hydrocarbon, we sometimes find that the system passes through several multiphase regions before reaching the microemulsion/oil/water equilibrium characteristic of optimal conditions. 

They utilize X-ray diffraction. X-ray diffraction allows direct qualitative and quantitative phase characterization — even in multiphase regions — and no potentially perturbing additives or molecular labels are needed. Although the high photon flux of synchrotron radiation is potentially damaging to the sample [15], particular parts need only be exposed to the beam for a short period of time and as a result, radiation damage is not a problem with this method. 

In order to emphasize the role of the inter facial films and to highlight the most recent viewpoints on the stability of microemulsions, sponge phases, and dilute lamellar phases, some of the experimental facts about phase behavior of microemulsion systems containing alcohol are reviewed in this chapter. The systems investigated consist of water, oil, alcohol, and sodium dodecylsulfate (SDS). In the next section, the theoretical aspects of the stability of surfactant phases are briefly discussed. Then in Secs. Ill and IV the effects of varying alcohol and oil chain lengths and the addition of a water-soluble polymer are examined. The examination of multiphase regions provides the location of lines of critical points or critical endpoints. This chapter also deals with the study of several physical properties in the vicinity of critical points. 

Figure 9 Sections at constant water/surfactant ratios X = 0.76,1.55, and 5.25 of the phase diagram of the water-dodecane-pentanol-SDS system (system B) at 21°C The hatched regions are the multiphase regions. P[ is a critical point. L and Lt are microemulsions is a lamellar phase L3.0 is an oil-rich sponge phase. (From Refs. 22 and 23.)...

Figure 15 Water-NaCl-dodecane-pentanol-SDS system effect of salinity on the microemulsion L2, lamellar L, and sponge L3 o- In the section considered, A = 1.55 and the dodecane content is 78 wt.%. The hatched regions represent multiphase regions. (From Ref. 105.)...

Fig. 13. Phase diagram for K adsorption on R(lll) [88P1]. In the multiphase region a continuous compression of the overlayer results in rotational epitaxy or aligned structures.

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