 Dukhin number

A dimensionless ratio comparing surface conduction with bulk conduction over a characteristic length. With pore radius r and surface conductance $K_s$, one convention is $\mathrm{Du}=K_s/(\sigma r)$; the cylindrical surface-to-bulk conductance ratio is twice this value.

The Dukhin number (Du) is a dimensionless quantity used in colloidal science and electrokinetics to describe the relative importance of electrokinetic effects and diffusion in a system containing charged particles, such as colloids or emulsions. It is named after the Russian scientist M. A. Dukhin, who contributed significantly to the understanding of electrokinetic phenomena.