Absence of anomalous exponents

Most critical phenomena do not follow simple mean field laws. For example, with small molecules (Nf, = Nb = ) our eq. (IV.24) for the correlation length is wrong. In this case the correct diverges as 

Fortunately these complications do not exist when both Na and Nb are large the mean field (Flory-Huggins) theory is qualitatively correct for polymer mixtures without solvent. This can be shown from a detailed study of fluctuation effects.We can summarize the results by the following statement, which is used often in this chapter. If we focus our attention on the species (A) with the longest chains (A/a Nb), each chain has a size Roa = o/Va and spans a volume / oa /Va . We now define a para- 

The scaling form of P is simple. The number of A chains per unit volume is 1/A/a nnd thus we have 

Since we are concerned primarily with the area around the critical point, we substitute the value of eq. (IV. 14) for 4 and fmd 

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