Intrinsic Viscosity vs. Relative Viscosity

Attribute	Intrinsic Viscosity	Relative Viscosity
Definition	Measure of a fluid's resistance to flow due to its molecular size and shape	Ratio of the viscosity of a solution to the viscosity of the solvent
Units	dl/g or L/g	No unit
Dependence on Concentration	Depends on concentration of the polymer in solution	Depends on concentration of the polymer in solution
Measurement	Measured by extrapolating the viscosity of a polymer solution to zero concentration	Measured by comparing the viscosity of a polymer solution to the viscosity of the solvent

Definition

Intrinsic viscosity and relative viscosity are both important parameters used in the field of polymer science to characterize the flow behavior of polymer solutions. Intrinsic viscosity is a measure of the inherent viscosity of a polymer solution, while relative viscosity is a measure of the viscosity of a polymer solution relative to the viscosity of the solvent. Both parameters are used to determine the molecular weight of polymers and to study their behavior in solution.

Calculation

Intrinsic viscosity is calculated using the following formula: η_sp = (η - η₀) / c, where η_sp is the specific viscosity, η is the viscosity of the polymer solution, η₀ is the viscosity of the solvent, and c is the concentration of the polymer in the solution. In contrast, relative viscosity is calculated as the ratio of the viscosity of the polymer solution to the viscosity of the solvent: η_r = η / η₀.

Units

Intrinsic viscosity is typically expressed in units of deciliters per gram (dL/g), while relative viscosity is a dimensionless quantity. Intrinsic viscosity is a measure of the flow resistance of a polymer solution per unit mass of polymer, while relative viscosity is a measure of the increase in viscosity of a polymer solution compared to the solvent alone. Both parameters provide valuable information about the molecular weight and structure of polymers.

Relationship to Molecular Weight

One of the key differences between intrinsic viscosity and relative viscosity is their relationship to molecular weight. Intrinsic viscosity is directly proportional to the molecular weight of the polymer, while relative viscosity is inversely proportional to the molecular weight. This means that as the molecular weight of a polymer increases, its intrinsic viscosity will also increase, while its relative viscosity will decrease.

Applications

Intrinsic viscosity is commonly used to determine the average molecular weight of polymers, as it provides a measure of the hydrodynamic volume of the polymer chains in solution. This information is crucial for understanding the physical properties and behavior of polymers in various applications. Relative viscosity, on the other hand, is often used to compare the viscosity of different polymer solutions and to study the effect of polymer concentration on viscosity.

Experimental Determination

Both intrinsic viscosity and relative viscosity can be determined experimentally using viscometers. Intrinsic viscosity is typically measured by plotting the specific viscosity as a function of polymer concentration and extrapolating to zero concentration. Relative viscosity, on the other hand, is measured directly by comparing the viscosity of the polymer solution to the viscosity of the solvent. These experimental techniques are essential for characterizing the flow behavior of polymer solutions.

Conclusion

In summary, intrinsic viscosity and relative viscosity are both important parameters used in polymer science to characterize the flow behavior of polymer solutions. While intrinsic viscosity provides information about the molecular weight and structure of polymers, relative viscosity is useful for comparing the viscosity of different polymer solutions. Both parameters play a crucial role in understanding the physical properties and behavior of polymers in various applications.