Critical dynamics in entangled binary mixtures

Critical dynamics in entangled binary mixtures 

We consider here a solution (or melt) with two types of polymer chains, A and B, and a slight incompatibility between A and B. We want to investigate the dynamics of the fluctuations of concentration 1 near the critical point in the one-phase region. Experimentally it will help if we add a fraction of solvent to the AB mixture, thereby decreasing the viscosities and relaxation times. However, for simplicity here we consider mly the case without solvent and a symmetrical situation (Na = Nb = AO- 

Dynamically, there is an essential difference between this case and the more common problem of one polymer plus one solvent. In the latter problem, near the critical point, backflow is essential, while entanglements are minor but with a molten mixture of chains, the situation is reversed backflow is negligible, and entanglements are essential. 

In practice what is measured is a cooperative diffusion coefficient Dg which controls the fluctuations of 1 according to  

When the Floiy interaction parameter x vanishes, the concentration is equalized by reptation and by tube renewal, and we expect to have, according toeq. (Vin.l4) 

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Vlll.3.4. Critical dynamics in entangled binary mixtures... 

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