Strictly speaking, you'd obviously have to use the solution's density. If the solution is dilute enough, its density will not be very different from the density of water so the latter may serve as a good approximation.

Thanks so much dear Till Kranz,

Viscosity is a measure of a fluids propensity to flow. There are two kinds of viscosity commonly reported, kinematic and dynamic. Dynamic viscosity is the relationship between the shear stress and the shear rate in a fluid. The Kinematic viscosity is the relationship between viscous and inertial forces in a fluid

Dynamic viscosity is measure of fluid's resistance to shear flow when some external force is applied. Kinematic viscosity is ratio of dynamic viscosity to density of that fluid. It is measure of fluid's resistance to shear flow under the weight of gravity.

In other words:

One way is to measure a fluid resistance to flow when an external force is applied. This is dynamic viscosity.

The other way is to measure the resistive flow of a fluid under the weight of gravity. The result is kinematic viscosity. Put another way, kinematic viscosity is the measure of a fluid’s inherent resistance to flow when no external force, except gravity, is acting on it.

Regards

Thanks dear Bachir

Dear Said,

You are welcome.

Regards

Thanks dear Ruben

Dynamic viscosity: The fluid’s resistance to flow when an external force is applied. Dynamic viscosity related to the external force applied to non-Newtonian fluids.

Kinematic viscosity: The fluid’s resistance to flow under the weight of gravity. The kinematic viscosity is calculated when no external force, except gravity, is acting on the polymer. Its value does not change with a change in applied force.

Two polymeric fluids that have the same dynamic viscosity can have different kinematic viscosity due to dependence of kinematic viscosity to the density of the fluid. Thus, if a very low concentration of polymer solution is prepared in order to consider the density of solution to the density of water or any type of solvent, a very big error would be happened in measuring the viscosity. Assuming the equality between the density of the polymer solution and the density of water causes the kinematic and dynamic viscosity would be the same. So, it is better to measure the dynamic viscosity directly by dynamic viscosity which is popular types of instruments used to measure dynamic viscosity. Moreover, it is possible to measure the density of polymer and one type of the viscosity and then calculate the other type of viscosity.

Falling piston viscometer, Rotational viscometer, Falling ball viscometer, and Vibrational viscometer are used to measure the dynamic viscosity of polymer solutions.