Gibbs free energy phase separation

Physical Equilibria and Solvent Selection. In order for two separate Hquid phases to exist in equiHbrium, there must be a considerable degree of thermodynamically nonideal behavior. If the Gibbs free energy, G, of a mixture of two solutions exceeds the energies of the initial solutions, mixing does not occur and the system remains in two phases. Eor the binary system containing only components A and B, the condition (22) for the formation of two phases is... 

It is apparent from early observations [93] that there are at least two different effects exerted by temperature on chromatographic separations. One effect is the influence on the viscosity and on the diffusion coefficient of the solute raising the temperature reduces the viscosity of the mobile phase and also increases the diffusion coefficient of the solute in both the mobile and the stationary phase. This is largely a kinetic effect, which improves the mobile phase mass transfer, and thus the chromatographic efficiency (N). The other completely different temperature effect is the influence on the selectivity factor (a), which usually decreases, as the temperature is increased (thermodynamic effect). This occurs because the partition coefficients and therefore, the Gibbs free energy difference (AG°) of the transfer of the analyte between the stationary and the mobile phase vary with temperature. 

Figure 7,8 Gibbs free energy curves and T-X phase relations for an intermediate compound (C), totally immiscible with pure components. Column 1 Gibbs free energy relations leading to formation of two eutectic minima separated by a thermal barrier. Column 2 energy relations of a peritectic reaction (incongruent melting). To facilitate interpretation of phase stability fields, pure crystals of components 1 and 2 coexisting with crystals C are labeled y and y", respectively, in T-X diagrams same notation identifies mechanical mixtures 2-C and C-1 in G-X plots.

We know from thermodynamics that spontaneous processes occur in the direction of decreasing Gibbs free energy. Therefore we may conclude that the separation of a two-phase dispersed system to form two distinct layers is a change in the direction of decreasing Gibbs... 

There are several approaches to derive the Gibbs free energy of micellization. We only discuss one of them which is called the phase separation model. Even this approach only leads to approximate expressions for nonionic surfactants. More detailed discussions of the thermodynamics of micellization can be found in Refs. [3,528,529],... 

Lipid bilayers are of fundamental importance in biology. All biological membranes are formed by lipid bilayers. They separate the interior of cells from the outside world and they separate different compartments in eucaryontic cells. Why are they such ideal structures for membranes Their main task is to avoid diffusion of polar molecules (such as sugars, nucleotides) and ions (in particular Ca2+, Na+, K+, and CP) from one compartment into another. The hydrophobic interior of the lipid bilayers efficiently achieves this. Polar molecules and especially ions cannot pass the hydrophobic interior. To transfer, for instance, an ion of radius R = 2 A from the water phase (ei = 78) into a hydrocarbon environment ( 2 = 4) the change in Gibbs free energy is [535]... 

The formation of uniform network polymers from lignin requires that phase separation prior to gel formation remain limited. The process of component demixing is controlled by both an enthalpic and an entropic contribution to Gibbs free energy. Whereas, the entropic factor requires the use of low molecular weight fractions for uniform gel formation, the enthalpic parameter necessitates chemical modification. The type of modification needed depends on the medium in which gel formation is performed. Examples of improving the solubility and compatibility with various reaction media are cited. 

Nearly all polymer blends undergo phase separation to some extent because of the small entropy gained and usual positive heat of mixing. Phase separation is controlled by the change in the Gibbs free energy of mixing, AFm, which is ... 

Phase separation and flocculation are similar, suggesting that the Gibbs free energy of mixing of a polymer with the solvent is responsible for both processes, and as a result, phase separation and flocculation have similar effects on heating and cooling. 

---