Quantities characterizing a multi-component medium

If the medium is made up of midtiple chemical species, then for each of those species, we define a charge per unit volume, a specific mass p., and a velocity If denotes the charge per unit mass (constant for a given species), we haiwe-.p = pz,. The mass flux of species in relation to a fixed frame of reference is  

For the mixture, we introduce average values. The charge per unit volxune is defined by  

The fluxes in relation to the barycentric motion are then defined, such as the diffusion flux (see Chapter 2 of [PRU 12])  

From a thermodynamic point of view, the state of each chemical species is characterized by the same variables as in non-conductive media (see Chapter 2 of [PRU12]). For example, species k is present at a concentration (mass fraction), a chemical potential per unit mass. The non-polarized conductive medium, with internal energy 

This result is no longer valid for polarized systems, as we shall see in Chapter 3. In a non-polarized medivun, the Gihbs equation given above can be written as a fvmction of other variables. Indeed, the Maxwell equations shown earlier enable us to write that the fields B and E depend on the scalar potential (p and the vector potential A such that  

---