Physics:Self-diffusion

According to IUPAC definition, self-diffusion coefficient is the diffusion coefficient [math]\displaystyle{ D_i^* }[/math] of species [math]\displaystyle{ i }[/math] when the chemical potential gradient equals zero. It is linked to the diffusion coefficient [math]\displaystyle{ D_i }[/math] by the equation: [math]\displaystyle{ D_i^*=D_i\frac{\partial\ln c_i}{\partial\ln a_i}. }[/math]

Here, [math]\displaystyle{ a_i }[/math] is the activity of the species [math]\displaystyle{ i }[/math] in the solution and [math]\displaystyle{ c_i }[/math] is the concentration of [math]\displaystyle{ i }[/math]. 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.

See also

• Brownian motion
• Diffusion
• Molecular diffusion