Middle soap phase

Middle soap phase, 22 726 Middlings, 16 603 Mid-ir lasers, 22 180 Mid-ir region, 14 234-236 MIDREX process, 14 513, 514 Midwest Research Institute, on PVC waste incineration, 25 681... 

Besides the lamellar liquid crystals just described, others are known to exist. We shall discuss only one here namely, the nematic liquid crystals illustrated by the middle soap phase of a typical soap-water system. An unoriented sample made up of many micro-liquid crystals of this sort will give a series of concentric... 

Figure 4.37 Phase diagrams of sodium cholate (NaC), water (W), lecithin (L). Systems (a) with no added cholesterol (b) with 0.5 % cholesterol (c) with 2 % cholesterol and (d) with 4% cholesterol. In the system without cholesterol the three paracrystalline phases are labelled I, II, and III. Phase I is analogous to neat soap of aqueous soap systems. Phase II is a cubic phase , and phase III is analogous to the middle soap phase of common soap systems. Phase IV is isotropic micellar system. X in diagram (b) represents the composition of normal human gall-bladder bile. From Small et al. [267, 268].

A mesomorphic (liquid-crystal) phase of soap micelles, oriented in a hexagonal array of cylinders. Middle soap contains a similar or lower proportion of soap (e.g., 50%) as opposed to water. Middle soap is in contrast to neat soap, which contains more soap than water and is also a mesomorphic phase, but has a lamellar structure rather than a hexagonal array of cylinders. Also termed clotted soap . See Neat Soap. 

Ekwall and Baltcheffsky [265] have discussed the formation of cholesterol mesomorphous phases in the presence of protein-surfactant complexes. In some cases when cholesterol is added to these solutions a mesomorphous phase forms, e.g. in serum albumin-sodium dodecyl sulphate systems, but this does not occur in serum albumin-sodium taurocholate solutions [266]. Cholesterol solubility in bile salt solutions is increased by the addition of lecithin [236]. The bile salt micelle is said to be swollen by the lecithin until the micellar structure breaks down and lamellar aggregates form in solution the solution is anisotropic. Bile salt-cholesterol-lecithin systems have been studied in detail by Small and coworkers [267-269]. The system sodium cholate-lecithin-water studied by these workers gives three paracrystalline phases I, II, and III shown in Fig. 4.37. Phase I is equivalent to a neat-soap phase, phase II is isotropic and is probably made up of dodecahedrally shaped lecithin micelles and bile salts. Phase III is of middle soap form. The isotropic micellar solution is represented by phase IV. The addition of cholesterol in increasing quantities reduces the extent of the isotropic... 

Fisher Scientific) was emulsified into aqueous soap solutions of 0.25 w% each of sodium laurate and sodium oleate prepared from sodium hydroxide, lauric acid (Aldrich Gold Label) and oleic acid (Fisher Purified). Coarse emulsions were used for microscopy (as in Figure 2), but fine emulsions (with droplet sizes of about 0.2 microns), used for determination of middle phase film thicknesses, were made by ultrasonication with a cell disruptor. 

Figure b. Time-dependence of interfacial tensions of oil drops spinning in 0.5% soap solutions (25°). Triangles - no salt. Hexagons and circles - 0.3 M salt. Squares - 0.4 M salt. Interfacial tensions rise as middle phase films are spun off. 

In a type 111 system, a left lobe or right lobe microemulsion cannot coexist with the middle-phase microemulsion. The total composition determines the existence of a lobe or the middle-phase microemulsion. Gary A. Pope (Personal communication on Febraary 17, 2009) pointed out that, as a practical matter, we rarely measure a sufficient number of points in the ternary system to clearly define two-phase and three-phase regions. When cosolvent and/or Ca is used, or when soap forms, a ternary diagram does not accurately represent the phase behavior. When typical salinity scans at WOR = 1 and a low surfactant concentration are performed, almost aU the cases in a type III environment will be three phases. So there is little, if any, practical issue involved in a typical phase behavior experiment. 

Rosevear, F. B., Amer. Oil Chem. Soc. J. (1954), 31, 628-639, "The Microscopy of the Liquid Crystalline Neat and Middle Phases of Soaps and Synthetic Detergents."... 

Finally, there is an interesting correlation between the values of 72(8/2) and molecular structure. For DC12AO the values of 72(8/2) are much greater than the Lorentzian value At 100° they are 5.5 for the neat phase and 4.5 for the middle phase. Sodium oleate (NaOl), which has a cis double bond in the middle of the chain, has considerably lower values of 72(8/2) for both middle (3.9) and neat (4.3) phases. The differences between the NaOl values and values found for saturated soaps are even greater. The lower values of 72(8/2) for NaOl indicate that the distribution of motions along the NaOl chain is more uniform. The double bond appears to act as another end, in effect making the chains much shorter. This is supported by the line width of NaOl (Table IV) which in the neat phase is roughly what one finds in a C12 — Cu chain. The double bond in the chain should have little effect in the middle phase. This appears to be borne out by both the 72(8/2) and line width data. The 72(8/2) for sodium elaidate... 

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