Extra Stress by Polymers

I Extra Stress by Polymers Adding a polymer to a solvent increases its viscosity. Fignre 3.50 iUnstrates a polymer chain in a shear flow. For the portion of 

DYNAMICS OF DILUTE POLYMER SOLUTIONS moving plate 

To estimate the intrinsic viscosity in the bead-spring model, we need to find how much the stress tensor in the flowing fluid changes when a unit amount of the polymer is added. At low concentrations, the increase in the stress tensor (a, /3 = x, y, z) due to the presence of bead-spring chains is given as 

In the Rouse model, there is no excluded volume effect. In the Zimm model for the theta solvent, the chain conformation is the same as that of the Rouse model. For these two models, U is given by a sum of the elastic energy of the springs (Eq. 1.51), and therefore 

It is now apparent that Acr = Acr a, as required. Although the last equation was derived for the ideal chain conformations, it is also valid for real chains with an excluded volume. 

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