Macroscopic and molecular shear viscosity

A brief review of the effect of Newton's macroscopic dynamic shear viscosity on the rotation of a cylinder and a ball in a viscous fluid is presented. The approximate nature of some of Stokes' formulae is discussed, and formulae from elementary viscosity theory are given. The concept of molecular viscosity is introduced, and it is shown that, among other information sources, spectra of depolarized molecular light scattering and electromagnetic wave dispersion in liquids of constant-dipole-moment molecules may, within a certain scheme, be used to derive the value and temperature dependence of the coefficient of shear dynamic molecular viscosity. As an example, the temperature behaviour of molecular viscosity in salol and o-terphenyl is presented and discussed qualitatively.