Chain-like molecular systems, mixing

Figure 3 Sketch for the mixing process of chain-like molecular systems (Xin et al., 2008c).

In real systems, nonrandom mixing effects, potentially caused by local polymer architecture and interchain forces, can have profound consequences on how intermolecular attractive potentials influence miscibility. Such nonideal effects can lead to large corrections, of both excess entropic and enthalpic origin, to the mean-field Flory-Huggins theory. As discussed in Section IV, for flexible chain blends of prime experimental interest the excess entropic contribution seems very small. Thus, attractive interactions, or enthalpy of mixing effects, are expected to often play a dominant role in determining blend miscibility. In this section we examine these enthalpic effects within the context of thermodynamic pertubation theory for atomistic, semiflexible, and Gaussian thread models. In addition, the validity of a Hildebrand-like molecular solubility parameter approach based on pure component properties is examined. 

In the slowly mixed system, the complex conformation is characterized by a worm-like helical chain or a randomly oriented zig-zag rod accompanied by the formation of braided double helices. The intramolecular side-by-side association of helices and inter-molecular entanglement are scarely developed due to the fractional mixing with a long interval periods exceeding the relaxation time for the rearrangement of hydrogen bonds. This may result in the exclusive formation of the A and A species by suppressing the formation of the B species due to extinction of the C species as an anchor. 

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