Qualitative features of polymer demixtion

2014 We consider three types of critical points associated with the segregation of long, flexible, polymer chains : 1) one polymer + poor solvent, 2) two molten polymer species without solvent, 3) two dilute polymer species in a good solvent. For all these cases the Flory Huggins theory (or its extensions) would lead to a classical (mean field) type of critical behaviour. We analyse the critical singularities more closely using a Ginsburg criterion, and conclude that in cases (1) and (3) the critical exponents are not classical. But in case (2), the Flory Huggins theory should apply, except for a minute temperature interval 0394T* near the critical point Tc [0394T* ~ Tc N-~, where N is the polymerization index, and ~ is a crossover exponent which we calculate for various situations]. LE JOURNAL DE PHYSIQUE LETTRES TOME 38, ler NOVEMBRE 1977, Classification Physics Abstracts 61.40 64.70