Mark–Houwink equation

The Mark–Houwink equation, also known as the Mark–Houwink–Sakurada equation or the Kuhn–Mark–Houwink–Sakurada equation or the Landau–Kuhn–Mark–Houwink–Sakurada equation or the Mark-Chrystian equation gives a relation between intrinsic viscosity ${\displaystyle [\eta ]}$ and molecular weight ${\displaystyle M}$:^[1][2]

${\displaystyle [\eta ]=KM^{a}}$

From this equation the molecular weight of a polymer can be determined from data on the intrinsic viscosity and vice versa.

The values of the Mark–Houwink parameters, ${\displaystyle a}$ and ${\displaystyle K}$, depend on the particular polymer-solvent system as well as temperature. For solvents, a value of ${\displaystyle a=0.5}$ is indicative of a theta solvent. A value of ${\displaystyle a=0.8}$ is typical for good solvents. For most flexible polymers, ${\displaystyle 0.5\leq a\leq 0.8}$. For semi-flexible polymers, ${\displaystyle a\geq 0.8}$. For polymers with an absolute rigid rod, such as Tobacco mosaic virus, ${\displaystyle a=2.0}$.

It is named after Herman F. Mark and Roelof Houwink.