Another useful expression is the specific viscosity, nsp, of the solution, defined by nsp - nrel - 1

For ideal solutions the ratio nsp/c (called the reduced viscosity) is independent of solution concentration. In real solutions the reduced viscosity varies with concentration owing to molecular interactions and it is usual to extrapolate plots of nsp/c versus c to zero concentration. The extrapolated value is called the intrinsic viscosity [n].

Einstein showed from hydrodynamic theory that for a dilute system of rigid, spherical particles

Box 8.1 Effect of shape and hydration on viscosity Effect of particle shape

A more general form of equation (8.6) allowing for particle asymmetry is nrd = 1 + vp (8.8)

where v is a shape factor related to the axial ratio of an ellipsoid. In the case of nonhydration spheres v reduces to 2.5. The volume is usually replaced by the weight concentration, c. For a macromolecule of hydrodynamic volume and molecular weight M

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