the two marks is recorded. This operation is repeated for increasingly dilute solutions of the same polymer/solvent. A duct parallel to the capillary allows pressure equilibration, so the flow of the fluid is only due to the hydrostatic head. Notice that the Cannon–Fenske viscometer [34] does not have the pressure equilibration duct, so it is not appropriate for accurate measurements of the intrinsic viscosity.
17.4.2.1 Measurement of the Intrinsic Viscosity The principle behind capillary viscometry is the Poiseuille’s law, which states that the time of flow of a polymer solution (ps) through a thin capillary is proportional to the viscosity of the solution. The latter increases with increasing solution concentration. From Equation 17.6, the time of flow of the solvent (solv) or of the polymer solution will be proportional to the viscosity, and inversely proportional to the density: