All species, except when the Immobile Species checkbox has been enabled, may be transported by diffusion, and charged species are also transported by migration in the electric field.

For dissociation species you can choose to set the transport parameters to be the Same for all species appearing in the different dissociation steps, or you can use Individual settings for each subspecies.

Typically the mobilities and diffusivities for small species are related by the Nernst–Einstein relation, and when this relation is enabled you can choose whether to specify either the Diffusivity (SI unit: m2/s) or the Mobility (SI-unit: s·mol/kg). The Debye–Hückel–Henry relation is commonly used for larger molecules, such as proteins.

If Mass transfer in porous media is enabled on the interface top node, you can use the settings of this section in the species nodes to account for the changed mass transport in a porous domain due to the lowered porosity and the increased tortuosity.

The default correction model is Bruggeman, which multiplies the diffusivity and mobility values by the porosity to the power of 1.5. The porosity of a domain is set by the Porous Matrix Properties node.

To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog.

The Debye–Hückel–Henry relation makes use of the ionic strength for calculating the species mobility from the diffusivity. All charged species contribute to the ionic strength, either assuming the species contributing to an Ideal solution or by using the Linderstrøm-Lang assumption. The latter is usually used for macromolecules.