Boger fluid

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In rheology , Boger fluids are among the non-Newtonian fluids because they have a measurable first normal stress . Like Newtonian fluids , however, they have a viscosity that is independent of the shear rate .

Boger fluids can be realized in the form of highly diluted polymer solutions , in which the shear thinning typical for polymer solutions and melts is negligible. The polymer chains are in shear of the fluid stretched in the direction of shear. If the flow is stopped, the polymer chains relax again to form an isotropic coil shape (on average) . This conformational change of the dissolved polymer chains causes macroscopically an elastic spring-back of the fluid.