For an isolated dissolved molecule or dispersed entity, an equation relating the translational diffusion coefficient, \(D\), to the equivalent hydrodynamic radius in translational diffusive flow, \(r_{D}\) , and to the viscosity of the solvent continuum or the dispersion medium continuum, \(\eta_{0}\), with \[D = kT/(6\uppi \eta_{0}r_{D})\] where \(k\) is the Boltzmann constant, and \(T\) the thermodynamic temperature.