Theoretical considerations about the critical demixtion point

1 Theoretical considerations about the critical demixtion point 

The theory concerning the top of the demixtion curve is well-understood in the case of binary mixtures of simple liquids. In general, to study the demixtion of polymer solutions, physicists contented themselves with a direct application of the theoretical results obtained for simple liquids. This classical approach will now be briefly described and subsequently a different approach will be expounded. 

1 A recapitulatory list of scaling laws concerning critical demixtion the case of simple binary liquids 

Critical phenomena can be grouped into classes. It is admitted that in the vicinity of their respective critical points, a binary mixture, a liquid-vapour system and the three-dimensional Ising model belong to the same class. The space dimension (d = 3) and the dimension of the order parameter (n = 1) are numbers characterizing the class. 

The order parameter associated with the demixtion phenomenon can be identified with the volume fraction cp — cpc, but one could also choose the concentration C - Cc. The best candidate should be the parameter leading to the most symmetrical demixtion curve. 

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