Demixing transition

More realistic approaches should, of course, comprise solvent models that give rise to electrostatic interactions. Shelley and Patey [273] used grand canonical MC simulations to investigate the demixing transition in model ionic solutions where the solvent is explicitly included. Charged hard-sphere ions in neutral, dipolar, and quadrupolar hard-sphere solvents were consi-... 

Aside from this, a comparison with the equilibrated mixture results shows that we are now dealing with a situation in which the partial quenching alters the behavior of the chemical potential, and to a much lesser extent the internal energy. As the dipolar density is increased, the HNC equation of the electrolyte breaks down. This is very likely due to a demixing transition, as we could conclude from the stability analysis carried out following the prescriptions of Chen and Forstmann [24, 28], According to them, it is possible to analyze the stability of the grand potential functional for the case of a ion-dipole mixture with equal size particles. The fluctuations in this quantity for the present case can be cast in the form [24],... 

Returning to our phase separation problem, if our system separates into two phases, we may consider them as the solvents of eq. (IV.l), and we see that a given type of chain will tend to go entirely into one of the two phases. Segregation effects will be very strong—too strong. First we must list cases where some compatibility can be maintained and where demixing transitions an be observed. 

Indeed, systematic experiments for both the strongly incompatible case poly( styrene)-poly (dimethylsiloxane) and the weakly incompatible case poly (styrene)-poly (methyl methacrylate) in various solvents seem to confirm well the scaling prediction Eq. (48). The prefactor reflects well the difference of the degree of incompatibility. Hence, because of the excluded volume correlation effects, for long chains, the demixing transition occurs well in the semidilute regime contrary to the predictions of the Flory-Huggins model. 

The scaling theory has been developed to explain critical phenomena and to account for the dramatic changes undergone by a system when approaching the order-disorder transition point. The phase transition in liquid crystals and the demixing transition of a two-Uquid mixture near LCST or UCST are two well-known examples of such order-disorder transition. 

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