Demixing flexibility

Fig. 8 Theoretical liquid-liquid demixing curve (solid line) and the bulk melting temperature (dashed line) of a flexible-polymer blend with one component crystallizable and with athermal mixing. The chain lengths are uniform and are 128 units, the linear size of the cubic box is 64, and the occupation density is 0.9375 [86]...

Schaink, H.M., Smit, J.A.M. (1997). Mean field calculation of polymer segment depletion and depletion-induced demixing in ternary systems of globular proteins and flexible polymers in a common solvent. Journal of Physical Chemistry, 107, 1004-1015. 

Another mechanism assuming the formation of connected, flexible, rod-like micelles is sometimes put forward to explain phase demixing (124). In this case, the phase separation results from an increase in the attraction due to the formation of junctions between the elongated aggregates. Nevertheless, this mechanism has not yet been evidenced experimentally in extractant systems. 

Fredrickson and co-workers have obtained entropic corrections to Flory-Huggins theory using a field theoretic approach. They considered athermal or nearly athermal blends where the corrections appeared from differences in the architecture or flexibility of the components. Using a field theoretic approach they demonstrated that conformational asymmetry will favor a demixing of the blends, and derived quasi universal conditions by which the miscibility could be maximized. Many qualitative features of the theory were consistent with experiments on polyolefin blends. This theory does not, however, attempt to rectify the many other approximations in the FH theory and is really intended only for nearly athermal blends, which are difficult to fabricate. 

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