Nonideal solutions, formation

Only one model to describe nonideal micelle Formation was described here. Regular solution theory in a diFFerent Form than that used here has been applied to these systems ( ). Alternative models have been proposed based on statistical mechanics (37.50). the... 

In an attempt to relate natural and model membranes, many lipid mixtures have been examined experimentally. It has been shown that additional components broaden the main phase transition, with a wider temperature range of coexisting gel and liquid phases (24). Another important feature of lipid mixtures is the formation of nonideal solutions with nonzero enthalpy... 

In this section we set up procedures that can be use later for constructing phase diagrams the results are also of intrinsic interest. We study the formation of a nonideal solution from its pure constituents these results should be contrasted with those of Section 2.5. 

Mixtures exhibiting nonideal solution behavior present both challenges and opportunities in connection with separation processes. Azeotropes cannot be separated by ordinary distillation, yet the formation of azeotropes itself may be used as a means for carrying out certain separations. The formation of two liquid phases in a column may complicate the separation process however, the coexistence of liquid phases with distinct compositions provides one more separation tool. Chemical reactions concurrent with distillation may be used either to enhance the separation or to perform both the reaction and the separation in one process. 

The two fundamental properties of surfactants are monolayer formation at interfaces and micelle formation in solution for surfactant mixtures, the characteristic phenomena are mixed monolayer formation at interfaces (Chapter 2, Section RIG) and mixed micelle formation in solution (Chapter 3, Section VIII). The molecular interaction parameters for mixed monolayer formation by two different surfactants at an interface can be evaluated using equations 11.1 and 11.2 which are based upon the application of nonideal solution theory to the thermodynamics of the system (Rosen, 1982) ... 

The last term is a thermodynamic correction factor for nonideal solutions. Equation M 5-23di predicts that Dab is not constant even for ideal systems [term in brackets in Eq. tl5-23di has a value of 1.0]. Equation ri5-23dl can also predict a negative diffusion coefficient, which is an indication of the formation of two liquid phases and is very important for liquid-liquid extraction. 

Equation 11.3 assumes that the solution is sufficiently dilute that it can be considaed to be ideal. For more concentrated solutions (> 0.05 M for singly charged species), ion-pair formation and other types of intermolecular interactions can lead to nonideal solution behavior, and the ion activities ( effective concentrations ) that go into Equation 11.2 will differ somewhat from the molarities. In that case, concentrations calculated from Equation 11.3 will deviate from the actual concentrations in the solution. 

In terms of Raoult s law, distinguish between an ideal liquid-liquid solution and a nonideal liquid-liquid solution. If a solution is ideal, what is true about AHsoi, AT for the solution formation, and the interactive forces within the pure solute and pure solvent as compared to the interactive forces within the solution Give an example of an ideal solution. Answer the previous two questions for solutions that exhibit either negative or positive deviations from Raoult s law. 

In Section 7.4.5.1, we simulate the formation of a nanoshell for the case of a nonideal solution. In Section 7.4.5.2, we study the crossover from formation to collapse, as well for nonideal solutions but for another average concentration, to obtain formation and collapse in one run at a reasonable computation time. In Section 7.4.5.3, we investigate mainly the segregation caused (kinetic origin) by the inverse Kirkendall effect for this reason, we treat an ideal solution in this subsection. 

While up to a certain degree solute-induced effects occur in all types of (nonideal) solutions, its manifestation in electrolyte systems deserves special attention. The presence of charged species in a dielectric solvent adds an important ingredient to the solvation phenomenon, i.e., the possible formation of neutral ion pairs. In fact, an outstanding property of water as a solvent at normal conditions is its intrinsic ability to solvate, and consequently dissolve, ionic and polar species, owing to its unusually large dielectric constant. This solvation process is typically described in terms of ion-solvent interactions, ion-induced solvent microstructural changes, solvent dielectric behavior, and their effects on the macroscopic properties of the solution. ... 

Some further details are the following. Film nonideality may be allowed for [192]. There may be a chemical activation barrier to the transfer step from monolayer to subsurface solution and hence also for monolayer formation by adsorption from solution [294-296]. Dissolving rates may be determined with the use of the radioactive labeling technique of Section III-6A, although precautions are necessary [297]. 

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... 

SOLUTION Reaction will take place in the direction that reduces the increase in pressure. (a) In the forward reaction, two N02 molecules combine to form one N204 molecule. Hence, compression favors the formation of N204. (b) Because neither direction corresponds to a reduction of gas-phase molecules, compressing the mixture should have no effect on the composition of the equilibrium mixture. (In practice, there will be a small effect due to the nonideality of the gases.)... 

Nonideality in aqueous solutions (see Chapter 3) was ascribed to Coulombic attraction between K and CCions, and the ion-ion interaction theories were evolved for aqueous solutions. The electrostatic attraction between a pair of oppositely charged ions could overwhelm thermal jostling and result in the formation of ion pairs (see Section 3.8). 

Nonideal Behavior. The discussion of phase behavior up to this point represents the ideal case. A number of factors cause deviation from ideality. The phases present may include liquid crystals, gels, or solid precipitates in addition to the oil, brine, and microemulsion phases (39, 40). The high viscosities of these phases are detrimental to oil recovery. To control the formation of these phases, the practice has been to add low-molecular-weight alcohols to the micellar solution these alcohols act as cosolvents or in some cases as cosurfactants. 

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