RPA-structure factor

The special situation of a homogeneous saddle point, corresponding to a homogeneous disordered phase, is particularly interesting. In that case, ex-phdt analytical relations between the single chain partition function and the fields can be obtained, and one recovers the well-known random phase approximation (RPA). To illustrate this approach, we shall now derive the RPA structure factor for the case of a symmetric binary homopolymer blend. 

Substituting these results into Eq. (7.94) gives the RPA-structure factor for a diblock copolymer melt... 

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