Lower critical solution temperature Macromolecular

Jhon, Y. K., Bhat, R. R., Jeong, C., Rojas, O. J., Szleifer, I., Genzer, J. (2006). Salt-induced depression of lower critical solution temperature in a surface-grafted neutral thermore-sponsive polymer. Macromolecular Rapid Communucations, 27, 697-701. 

On the other hand, the same model does not predict the lower critical solution temperature case (LOST), which is observed in macromolecular solutions with polar components. Indeed, demixing upon an increase of the temperature (Figure 4.4) is a well-known phenomenon for solutions of polar polymers that are characterized by a high enthalpy of mixing. Conscious of this shortcoming, Hory modified the initial version of his model and reconsidered the assumptions of an enthalpy of mixing and of an energy of contact independent of the temperature. 

It is well known that the possible causes for the presence of lower critical separation phenomena in polymer solutions have been associated with differences in free volume between the solvent and the macromolecular solute in the vicinity of the solvent critical point. Another possible reason for the appearance of lower critical phenomena in aqueous polymer solutions has been identified with the circumstance that at moderate temperatures hydrophobic interactions among polymer chains could be developed. In the later case, the behaviour of phase separation should be related with the existence of hydrogen bonding as well. 

Simple in its use, this model describes appropriately the behavior of polymer blends and of concentrated macromolecular solutions. It predicts the change in volume resulting from the mixing and also the existence of lower and higher critical temperatures of phase separation when there is a great disparity in the size of components 1 and 2. At high pressure and/or low temperature (p->- 1), this model is close to that of Flory-Huggins. 

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