Self-diffusion

According to IUPAC definition, self-diffusion coefficient is the diffusion coefficient D i ∗ {displaystyle D_{i}^{*}} of species i {displaystyle i} when the chemical potential gradient equals zero. It is linked to the diffusion coefficient D i {displaystyle D_{i}} by the equation: According to IUPAC definition, self-diffusion coefficient is the diffusion coefficient D i ∗ {displaystyle D_{i}^{*}} of species i {displaystyle i} when the chemical potential gradient equals zero. It is linked to the diffusion coefficient D i {displaystyle D_{i}} by the equation: D i ∗ = D i ∂ ln ⁡ c i ∂ ln ⁡ a i . {displaystyle D_{i}^{*}=D_{i}{frac {partial ln c_{i}}{partial ln a_{i}}}.} Here, a i {displaystyle a_{i}} is the activity of the species i {displaystyle i} in the solution and c i {displaystyle c_{i}} is the concentration of i {displaystyle i} . This term is commonly assumed to be equal to the tracer diffusion determined by watching the movement of an isotope in the material of interest.