Lattice Model Treatments of the Formation of Ordered Phases in Stiff Chain Polymer-Diluent Systems
The Flory-Huggins lattice treatment has been the cornerstone for many years for understanding the solution thermodynamics of flexible polymers. The effect of chain stiffness was investigated by Flory, again using a lattice approach,1,2 where the stability of both ordered and disordered phases was considered. The phase equilibria for a rigid rod-diluent system, plotted as the volume fraction vi, are shown in Figure 1 for a rod of 150 axial ratio, where χ is the van Laar polymer-solvent heat of mixing parameter. Alternatively, χ may be looked upon as proportional to the excess free energy of mixing.
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