Origin of the Cerf friction

Three microscopic explanations have been reported for the fiiction term f, [eq. (VI. 104)]. 

When W,6(p / N) is much larger than unity 1 / reaches a plateau (1 / 0). At intermediate values of p/N there is an inflection point in the plot of 1/tp versus p/N. If by accident we are operating in this region for p = 1, the apparent dependence of l/xp on l/N may be linear. 

In Fig. VI. IS we see two monomers (n) and (m) which are accidentally in close contact although the chemical distance n - m is large. If we pull on the chain extremities, the two monomers (n) and (m) will slide onto each other, and friction will occur. This monomer-monomer friction does not involve the solvent, but will be somewhat related to the viscosity of a fluid of monomers. 

We obtain a rough estimate of the friction by the following procedure. If the total elongation is r and its time derivative f = dr/dt, we assume that the chain deforms according to a linear law  

Thus the resulting friction coefficient is of order N we recover the Kuhn theorem. 

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