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 η i n h = ln η r e l c {\displaystyle \eta _{inh}={\frac {\ln \eta _{rel}}{c}}} where c {\textstyle c} is the mass concentration of the polymer and η r e l {\textstyle \eta _{rel}} is the relative viscosity, which is defined as η r e l = η η s {\displaystyle \eta _{rel}={\frac {\eta }{\eta _{s}}}} where η {\textstyle \eta } is the viscosity of the solution and η s {\textstyle \eta _{s}} is the viscosity of the solvent. The definition of η inh {\textstyle \eta _{\text{inh}}} is a finite difference approximation to the derivative d ( ln ( η ) ) d c | c = 0 {\displaystyle \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.
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