In polymer science, inherent viscosity is the ratio of the natural logarithm of the relative viscosity of a polymer to its mass concentration.[1] Inherent viscosity scales inversely to mass density, and a common unit is dL/g.
Inherent viscosity is defined as [2] η η --> i n h = ln --> η 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 η --> r e l {\textstyle \eta _{rel}} is the relative viscosity, which is defined as η η --> r e l = η η --> η η --> s {\displaystyle \eta _{rel}={\frac {\eta }{\eta _{s}}}} where η η --> {\textstyle \eta } is the viscosity of the solution and η η --> s {\textstyle \eta _{s}} is the viscosity of the solvent.
The definition of η η --> inh {\textstyle \eta _{\text{inh}}} is a finite difference approximation to the derivative d ( ln --> ( η η --> ) ) d c | c = 0 {\displaystyle \left.{\frac {d(\ln(\eta ))}{dc}}\right|_{c=0}} That ideal limiting value is the intrinsic viscosity,[3][4] which is a good measure of the polymerization degree.[5][6]
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