Fick's Laws of Diffusion

Two continuum relations describing molecular or ionic transport driven by concentration differences: Fick's first law gives steady-state diffusive flux J = −D∇c (flux proportional to the spatial concentration gradient and the diffusion coefficient D); Fick's second law gives time-dependent concentration change ∂c/∂t = D∇²c for homogeneous, constant-D media (or its generalized form when D varies sp