Phase behavior environments

Fang J, Lyon DY, Wiesner MR, Dong J, Alvarez PJJ (2007) Elfect of a fullerene water suspension on bacterial phospholipids and membrane phase behavior. Environ. Sci. Technol. 41 2636-2642. 

Phase Behavior. Nelson and co-workers (23-25) and Healy et al. (26) have written extensively on phase behavior in micellar flooding. In Nelson s methodology, three different phase-behavior environments occur... 

Figure 5. Phase-behavior environments. (Reproduced with permission from reference 24. Copyright 1978 Society of Petroleum Engineers.)...

It is generally known that the examined properties and phase behavior of ILs vary on cation and anion structures changing. Some typical trends will be presented in this chapter on the basis of the structural effect on the interactions between counterpart ions (see, for example Ref. 3, the spoon-shaped structure of the unit cell of the l-dodecyl-3-methylimidazolium hexafluoro-phosphate, [Ci2Cilm][PFg]), and between the IL and the solvent, or the coexisting compound. The structure of IL and its interaction with the environment is extremely important in applications in analytical chemistry [4]. 

Water-based solvent systems originally developed for the separation and purification of proteins and other biomaterials (Walter et al., 1985) have been suggested for the treatment of contaminated aqueous waste-streams. Certain pairs of water-soluble polymers are incompatible in solution together, and this can lead to phase separation in which two phases are formed. Both phases are predominantly water, and each contains only one of the two polymers. Similar phase behavior results with some polymers and high concentrations of organic salts. The properties of the two phases ensure that the environment-afforded targeted species is different in the two phases. 

Experimental, theoretical, and computational investigations of molecular interactions in supercritical mixtures (1-17) have led to a growing body of evidence suggesting that in typical supercritical mixtures the local environment surrounding solute molecules can be considerably different from the bulk. A molecular-based understanding of these systems is essential to develop accurate predictive models of their phase behavior. 

Zimmerman, J. B. Kibbey, T. C. G. Cowell, M. A. Hayes, K. F. "Partitioning of Ethoxylated Nonionic Surfactants into Nonaqueous-Phase Organic Liquids Influence on Solubilization Behavior," Environ. Sci. Technol, 1999,33, 169-176. 

Once such systems are better understood, NMR may be useful in experimental perturbation of the model. For example, the addition of deuter-ated penetration enhancers would allow study of the various environments experienced by such molecules and for the same system, phase behavior can be monitored by similar or other means (e.g., x-ray diffraction, FTIR, DSC). As illustrated by the studies in this volume, a combination of physical methods is likely to lead to a rigorous understanding of the basis of the epidermal permeability barrier and thus to rational therapeutic intervention. 

Figure 6.11 shows the activity of an artificial enzyme can be controlled based on the phase behavior of a lipid bilayer. The catalytic site for hydrolysis was supplied by a monoalkyl azobenzene compound with a histidine residue which was buried in the hydrophobic environment of a hpid bilayer matrix formed using a dialkyl ammonium salt. Azobenzene compound association depended on the state of the matrix bilayer. The azobenzene catalyst aggregated into clusters when the bilayer matrix was in a gel state. In contrast, the azobenzene derivative can be dispersed into the liquid crystalhne phase of the bilayer matrix above its phase transition temperature. This bilayer-type artificial enzyme catalyzed the hydrolysis of a Z-phenylalanine p-nitrophenyl ester. The activation energy for this reaction in the gel state is twice as large as that observed in the hquid crystalline state. The clustering of the catalysts upon phase separation suppress their catalytic activity, probably due to the disadvantageous electrostatic environment around the catalysts and the suppressed substrate diffusion. This activity control is unique to such molecular assembhes. 

Figure 6 shows an idealized salinity requirement diagram. Within the type III phase environment, three phases occur in the area indicated, but two phases occur in the rest of the type III region. Type II(+) phase behavior occurs above the type III region, and the type II(-) behavior occurs below. Midpoint salinity is shown near the middle of the type III region. 

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. 

This section describes how to use Hand s rule to represent binodal curves and tie lines. The surfactant-oil-water phase behavior can be represented as a function of effective salinity after the binodal curves and tie lines are described. Binodal curves and tie lines can be described by Hand s rule (Hand, 1939), which is based on the empirical observation that equilibrium phase concentration ratios are straight lines on a log-log scale. Figures 7.15a and 7.15b show the ternary diagram for a type II(-) environment with equilibrium phases numbered 2 and 3 and the corresponding Hand plot, respectively. The line segments AP and PB represent the binodal curve portions for phase 2 and phase 3, respectively, and the curve CP represents the tie line (distribntion cnrve) of the indicated components between the two phases. Cy is the concentration (volnme fraction) of component i in phase) (i or j = 1, 2, or 3), and 1, 2, and 3 represent water, oil, and microemulsion, respectively. As the salinity is increased, the type of microemulsion is changed from type II(-) to type III to type II(-i-). C, represents the total amount of composition i. 

Here, we described the general procedure to quantify phase behavior for type ll(-) and type II(-f) systems. For the type 111 phase environment with middle-phase microemulsion, the phase compositions are fixed at the invariant point (Cim, C2M, Csm). The subscript M denotes the invariant point, and Qm (i = 1,2, 3) is the composition at the invariant point. What are the invariant compositions then ... 

Two-Phase Approximation of Phase Behavior without Type III Environment... 

Baran, J.R., Pope, G.A., Wade, W.H. and Weerasooriya, V. (1996) Water/chlorocarbon winsor I III II microemulsion phase behavior with alkyl glucamide surfactants. Environ. Sci. Technol, 30(7), 2143-2147. 

Phase behavior in multiphase environments. Many reaction systems either occur in a multiphase environment or form products that will exist in a different phase. The description of how species are divided up into different phases is a key element of reaction engineering and often the more challenging one. 

The Phase Behavior Modeling of Chemicals in the Environment 693 is approximately 40 percent of the octanol-water partition coefficient that is,... 

The Phase Behavior Modeling pf Chemicals in the Environment 689 Problems for Section 12.5 695... 

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