Page "Molecular diffusion" Paragraph 1

Molecular diffusion, often called simply diffusion, is the thermal motion of all ( liquid or gas ) particles at temperatures above absolute zero.

The rate of this movement is a function of temperature, viscosity of the fluid and the size ( mass ) of the particles.

Diffusion explains the net flux of molecules from a region of higher concentration to one of lower concentration, but it is important to note that diffusion also occurs when there is no concentration gradient.

The result of diffusion is a gradual mixing of material.

In a phase with uniform temperature, absent external net forces acting on the particles, the diffusion process will eventually result in complete mixing.