Discussion
Which one of the following permits the direct determination of intrinsic viscosity of a polymer solution for known molecular weight of the polymer?
Answer: D
The relation is the Mark-Houwink equation.
The Mark-Houwink (Mark-Houwink-Sakurada) equation links intrinsic viscosity directly to molecular weight:
\[ [\eta] = K M^{a} \]
where K and a are constants for a given polymer, solvent and temperature. With M known, \([\eta]\) follows at once; used the other way, it is how viscometry gives the viscosity-average molecular weight.
The Flory-Huggins equation describes the free energy of mixing of a polymer solution, not its viscosity. Newton's law of viscosity only defines viscosity as shear stress over shear rate. The Williams-Landel-Ferry equation describes how viscosity or relaxation times shift with temperature above the glass transition.
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