Question

Which one of the following measures of viscosity is dimensionless?

• A. Inherent viscosity
• B. Reduced viscosity
• C. Zero-shear viscosity
• D. Specific viscosity

Hint:

In polymer solutions, {specific viscosity} is the most commonly used dimensionless quantity to describe the effect of solutes on the solution's viscosity. It helps in understanding the interaction between the polymer and solvent.

Answer 1

The Correct Option is D

Viscosity is an important property of fluids, describing the resistance of a fluid to flow. When studying polymer solutions, viscosity can be measured in various forms. Some forms of viscosity have dimensions, while others are dimensionless.
- Inherent viscosity is defined as the natural logarithm of the ratio of the viscosities of a solution and the solvent, divided by the concentration of the solute. This quantity is dimensionless, but it is not a direct measure of viscosity itself.
- Reduced viscosity is the ratio of the specific viscosity to the concentration of the solute. It is also dimensionless and provides an important measure of how the presence of a solute affects the viscosity of a solution.
- Zero-shear viscosity refers to the viscosity at very low shear rates, often used in the study of high molecular weight polymers. It is important in rheology, but it is not dimensionless.
- Specific viscosity is defined as the ratio of the increase in viscosity due to the solute to the viscosity of the pure solvent. Since it compares relative viscosities, it is dimensionless by definition.
Among the options, specific viscosity is the only dimensionless measure of viscosity. Therefore, the correct answer is (D) Specific viscosity.