Critical phenomena polymer blend phase separation

Polymer blends may be characterized in terms of the temperature dependence of the Flury-Huggins interaction parameter (j)- In the case of an upper critical solution temperature (UCST) blend, / decreases with temperature, and the blend remains miscible. For phase separation to occur in a UCST blend, the temperature must be lower than the critical solution temperature. In the case of a lower critical solution temperature (LCST) blend, x increases with temperature, and thus phase separation occurs above the critical solution temperature. The ability of CO2 to mimic heat means that miscibility is enhanced in the case of UCST blends, and for the case of LCST blends the miscibihty is depressed. Ramachandrarao et al. [132] explained this phenomenon by postulating a dilation disparity occurring at higher CO2 concentration as a result of the preferential affinity of CO2 to one of the components of the blend, inducing free-volume and packing disparity. 

---