Orientation-induced spinodal

On the other hand, in a polydisperse melt a spinodal instability would be expected eventually to reach biphasic equilibrum, in which case standard Cahn-Hilliard kinetics would be expected. Phase separation could be due to several effects, including chemical polydispersity, coupling of mass density to the density of polymer ends, and conformation-density-orientation coupling, which has a natural prediliction for inducing phase separation (longer chains are, per unit monomer, more nematic than their short chain cousins ). There are evidently several effects to sort out, and close collaboration between theory and experiment will help to attack the various mechanisms. 

Brochard and de Gennes [67] discussed theoretically a flow-induced isotropic-mesophase transition in a polydisperse polymer system occurring through spinodal decomposition. Following Maier-Saupe s [50] theory of the nematic phase, the orientation-dependent interaction energy was taken as... 

These results indicate that spinodal decomposition can be induced by flow even in a homopolymer system, which results in an oriented nematic phase with long chains and an isotropic liquid with short chains. Though the above argument is based on a bimodal system, the same principle has also been applied to the polydisperse case [67]. However, this approach still does not take flow-induced conformational ordering into account, which may couple to the anisotropic interactions. 

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