Self-diffusion

Self-diffusion describes the diffusive motions of molecules within themselves e.g. the movement of a water molecule in water. According to the IUPAC definition, the self-diffusion coefficient D_i^* of medium i is the diffusion coefficient D_i of a chemical species in said medium when the concentration of this species is extrapolated to zero concentration. It can be described by the equation:

D_i^* = D_i\frac{\partial\ln c_i}{\partial\ln a_i}