Phase diagram, water

Fig. 1. Binary soap—water phase diagram for sodium palmitate (4). Courtesy of Academic Press, Ltd.

It would be incomplete for any discussion of soap crystal phase properties to ignore the colloidal aspects of soap and its impact. At room temperature, the soap—water phase diagram suggests that the soap crystals should be surrounded by an isotropic Hquid phase. The colloidal properties are defined by the size, geometry, and interconnectiviness of the soap crystals. Correlations between the coUoid stmcture of the soap bar and the performance of the product are somewhat quaUtative, as there is tittle hard data presented in the literature. However, it might be anticipated that smaller crystals would lead to a softer product. Furthermore, these smaller crystals might also be expected to dissolve more readily, leading to more lather. Translucent and transparent products rely on the formation of extremely small crystals to impart optical clarity. 

FIG. 2 Example media (a) Surfactant-water phase diagram. (Reprinted from Ref. 206, Copyright 1991, with permission from Elsevier Science.) (b) Ordered periodic and bicontinuous structures. (Reprinted from Ref. 178 with permission from Academic Press, Ltd.) (c) Nonordered membrane structures from ternary microemulsions. (Reprinted with permission from Ref. 177, Copyright 1989, American Chemical Society.)... 

Amperometric cells, sensors using, 22 271 Amperometric measurements, 14 612 Amphetamine, 3 89-90 Amphibole asbestos, 1 803 3 288 crystal structure, 3 297-298 exposure limits, 3 316 fiber morphology, 3 294-295 silicate backbone, 3 296 Amphibole potassium fluorrichterite, glass- ceramics based on, 12 637 Amphiphile-oil-water-electrolyte phase diagram, 16 427-428 Amphiphile-oil-water phase diagrams,... 

Figure 13.4 Low-level 18-cluster QCE model (RHF/3-21G level) of the water phase diagram, showing (above) the dominant W24 clathrate-type cluster of the ice-like solid phase, and (below) the overall phase diagram near the triple point (with a triangle marking the actual triple point). Note that numerous other clusters in the W2o-W26 range were included in the mixture, but only that shown (with optimal proton ordering) acquired a significant population.

Silica-CTAB-Water Phase Diagram at 150 °C Predicting Phase Structure by Artificial Neural Network... 

See Section 4.1.5 for other examples of how Gibbs Phase Rule works in the methane + water phase diagram. Section 5.2 shows the application of the Gibbs Phase Rule for hydrate guests of methane, ethane, propane, and their mixtures. 

The phase behavior of hydrocarbon + water mixtures differs significantly from that of normal hydrocarbon mixtures. Differences arise from two effects, both of which have their basis in hydrogen bonding. First, the hydrate phase is a significant part of all hydrocarbon + water phase diagrams for hydrocarbons with a molecular size lower than 9 A. Second, water and hydrocarbon molecules are so different that, in the condensed state, two distinct liquid phases form, each with a very low solubility in the other. 

Lyophilization employs sub-zero temperatures in combination with very low pressure to withdraw water from the protein solution typical values would be -80 °C and 1-3 mbar. In these conditions, as the water phase diagram reveals, water sublimes, leaving a fluffy porous enzyme powder. As typical run times are on the order of a day, lyophilization is not the method of choice for large-scale enzyme drying operations. On a laboratory scale, however, lyophilization is a very effective method. 

A2B melts to a liquid of the same composition as the compound. We say that it melts congruently. Some compounds melt incongruently, (i.e., to liquids of a different composition). This behavior is illustrated by the compound NaOH 2H20 in the NaOH-water phase diagram shown in Fig. 12.3... 

FIGURE 15 PEG 3400-dextran 500-water phase diagram at 4°C. (Reprinted with permission from Diamond and Hsu.4 Copyright 1992 Springer Verlag.)... 

Figure 3. Schematic representation of a phospholipid-water phase diagram. The temperature scale is arbitrary and varies from lipid to lipid. For the sake of clarity phase separations and other complexities in the 20-99% water region are not indicated. Structures proposed for the phospholipid bilayers at different temperatures are shown on the right-hand side. At low temperature, the lipids are arranged in tilted one-dimensional lattices. At the pre-transition temperature, two-dimensional arrangements are formed with periodic undulations. Above the main phase, transitions lipids revert to one-dimensional lattice arrangements, separated somewhat from each other, and assume mobile liquid-like conformations.

DMSO has a freezing point of 18 °C. The eutectic of water and DMSO (30% HjO) has a freezing point of about —70 °C. To ensure freezing of the millimolar compound solutions in DMSO at —20 °C, the solvent DMSO has to be nearly water-free, i.e. it should contain no more than a few percent water. Details on the DMSO/water phase diagram can be found in Ref. 4. 

Figure 2 Illustrative lyotropic lipid-water phase diagram for phospholipid amphiphiles with transitions between the phase ranges driven by the water content. Hatched areas indicate two-phase regions (reproduced from (52) with permission from Elsevier).

An illustration of a lipid-water phase diagram, in which the transitions are driven by water content, is shown in Fig. 2 (43). A similar phase sequence can be produced by changes in temperature as well, and phospholipid phase diagrams generally exhibit pronounced temperature dependence. A generalized phase sequence of thermotropic phase transitions for the typical membrane lipids can be defined (44) ... 

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