Fuoss-Kirkwood curves

Many symmetrical loss relaxation curves fit the so-called Fuoss-Kirkwood (FK) equation given by... 

Treating the problem as one of rotary Brownian movement, Kirkwood and Fuoss were able to calculate the distribution functions and F (r) of Eqs. 22 and 29. In their case F(r) was a symmetrical function and they identified the average relaxation time with the value corresponding to the maximum in the loss curve. Unfortunately their theory is incompatible with existing experimental data on dilute solutions, since it specifies that should be proportional to the degree of polymerization. 

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