Inherent viscosity

In polymer science, inherent viscosity is the ratio of the natural logarithm of the relative viscosity of a polymer to its mass concentration. Inherent viscosity scales inversely to mass density, and a common unit is dL/g.

Inherent viscosity is defined as $$\eta _{inh}={\frac {\ln \eta _{rel}}{c}}$$ where ${\textstyle c}$ is the mass concentration of the polymer and ${\textstyle \eta _{rel}}$ is the relative viscosity, which is defined as $$\eta _{rel}={\frac {\eta }{\eta _{s}}}$$ where ${\textstyle \eta }$ is the viscosity of the solution and ${\textstyle \eta _{s}}$ is the viscosity of the solvent.

The definition of ${\textstyle \eta _{\text{inh}}}$ is a finite difference approximation to the derivative $$\left.{\frac {d(\ln(\eta ))}{dc}}\right|_{c=0}$$ That ideal limiting value is the intrinsic viscosity, which is a good measure of the polymerization degree.