<Dl> <Dd> J = − D ∇ n, J i = − D ∂ n ∂ x i . (\ displaystyle \ mathbf (J) = - D \ nabla n \, \; \; J_ (i) = - D (\ frac (\ partial n) (\ partial x_ (i))) \ .) </Dd> </Dl> <Dd> J = − D ∇ n, J i = − D ∂ n ∂ x i . (\ displaystyle \ mathbf (J) = - D \ nabla n \, \; \; J_ (i) = - D (\ frac (\ partial n) (\ partial x_ (i))) \ .) </Dd> <P> The corresponding diffusion equation (Fick's second law) is </P> <Dl> <Dd> ∂ n (x, t) ∂ t = ∇ ⋅ (D ∇ n (x, t)) = D Δ n (x, t), (\ displaystyle (\ frac (\ partial n (x, t)) (\ partial t)) = \ nabla \ cdot (D \ nabla n (x, t)) = D \ Delta n (x, t) \,) </Dd> </Dl>

What is the significance of diffusion in the molecular theory of matter