Demixing completely mixed

After eqn.(3.14) turned out to be obeyed by many systems in practice, a model was developed that could provide a physical picture. This so-called diachoric model [306] explains the fact that the two components of the mixed phase behave independently by demixing on a microscopic scale. Hence, the stationary phase is assumed to consist of little patches or droplets of either pure A or pure B. Obviously, such a model does explain obeyance of eqn.(3.14), while it also gives a handle to explain deviations from linearity in terms of complete mixing of the two phases. 

The MD simulations D - J focus on the demixing of completely mixed water/ C02/TBP/acid systems, which are "chaotic arrangements", also prepared by MD simulations (see methods). These systems, "perfectly mixed" at the microscopic level (probably more than they are in reality) are highly unstable. We want to investigate how they spontaneously evolve and relax, and in particular to which extent the aqueous and CO2 phases will separate, and how the acid and uranyl nitrate species will distribute once the equilibrium is reached. One critical issue, in relation with assisted extraction, is whether and under which conditions uranyl will be complexed by TBP and finally extracted to CO2. The pH-neutral D and E systems, described in more details in ref (28) are presented here for a purpose of comparison with the acidic ones F-J. 

Figure 10 Time evolution of the demixing of [C4mim][Tf2N] (designated in the figure as [BMI][Tf2N]) and TIP3P water, starting from completely mixed liquids. Snaphots are shown at different times, with the liquid components shown side by side for clarity. (Image from Ref. 90 and used with permission.)...

Temperature quench is not always a viable route to form structures since this approach requires the blend components to be thermally stable in the one- and two-phase region for a sufficiently long time. In effect, thermal stability is required in order to both ensure complete mixing in the homogeneous state and permit the formation of an equilibrium structure in the demixed state [14]. In addition to the thermal stability, the wetting properties of the polymers employed for the blend plays a key role. The coated polymers do not always wet the substrate and therefore dewetting competes with phase separation [71]. In those blends having components with a limited stability in relation to tanperature, the use of solvent to improve the phase separation can, at least to some extent, overcome these limitations. 

The action of phospholipase A2 on mixed monolayers of natural and polymerizable lipids can be measured under constant surface pressure by the contraction of the monolayer as a function of time as depicted schematically in Fig. 39. It turns out that the chief parameter influencing the enzymatic activity is the miscibility of the lipid components and not the fact whether the film is polymerized or not. In mixed and demixed membranes the enzyme is able to hydrolyze the natural lipid component, but with considerable differences in the hydrolizing rate (Fig. 40). A pure dilauroyllecithin (DLPC) monolayer is completely hydrolyzed in a few minutes after injecting the enzyme... 

Figure 20 A triblock copolymer (a) with two outer hydrophilic blocks that can self-assemble into mixed micelles (b), partly demixed or multicompartment micelles (c), or completely demixed, biphasic Janus micelles (d). The amphiphilicity on triggering the hydrophilic to hydrophobic transition may result in superstructure formation. (Reproduced from Ref. 49. American Chemical Society, 2010.)...

Liquid/solid Equilibria. The solubility of crystalline polymers is normally considerably lower than that of amorphous polymers because they require an additional energy, namely, the heat of fusion, in order for the bulk polymer to mix with solvent. Fig. 6 shows as an example the behavior of semi crystalline polyethylene in two different solvents(20). The solvent xylene is favorable in the temperature range of interest (no liquid/liquid demixing) up to the melting temperature T. o of the pure polymer a saturated solution coexists with the crystalline polyethylene and the components are completely miscible once T has surpassed Tm,o- Nitrobenzene on the other hand, is thermod5mamically less favorable and exhibits liquid/liquid demixing in addition to the solid/liquid phase separation. In this case one observes the coexistence of three phases at a characteristic temperature (broken line in Fig. 6) and concentration. 

Fig. 7.6 Critical micelle concentrations for mixtures of sodium perfluorooctanoate with sodium decyl sulfate (A) and sodium laurate (O). Dashed lines represent expected values for Ideal mixing, assuming B = 0.645 [Eq. (6)]. Curves 1, 2, 3, and 4 show expected values for complete demixing of micelles [Eq. (7)]. Curve 1 was calculated for B = 0.53 curves 2, 3, and 4 were calculated assuming B = 0.645. (From Ref. 68. Reproduced by permission of the American Chemical Society.)...

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