Fick’s Law of Diffusion describes how particles under random thermal motion tend to spread from a region of higher concentration to a region of lower concentration. In 1855, Adolf Fick described Fick’s Law of Diffusion. A diffusion process that obeys Fick’s laws is called normal diffusion or Fickian diffusion. A diffusion process that does not obey Fick’s laws is known as Anomalous diffusion or non-Fickian diffusion.
The net diffusion rate of a gas across a fluid membrane is proportional to the difference in concentration, to the surface area of the membrane, to the permeability of the membrane to the substance, and inversely proportional to the thickness of the membrane and molecular weight of the molecule.
This principle is illustrated by opening a perfume bottle in the corner of a closed room. If you wait long enough, the perfume odor will permeate the room because the perfume molecules have diffused from one side of the room to the other, from a region of high concentration to a region of low concentration.
Table of Contents
Fick’s First Law
Mathematically, three-dimensional diffusion is characterized by Fick’s diffusion law, which states that the diffusion flux is proportional to the concentration gradient, as :
Movement of solute from higher concentration to lower concentration across a concentration gradient.
J=−D dφ/dx
Where,
J: diffusion flux
D: diffusivity
φ: concentration
x: position
Fick’s Second Law
Prediction of change in concentration along with time due to diffusion.
∂φ/∂t =D ∂2φ/∂x2
Where,
D: diffusivity
t: time
x: position
Φ: concentration
Therefore, charged particles tend to flow down a concentration gradient. This diffusion process also occurs in PN junctions whenever there are gradients of free-charged carriers.
Application of Fick’s law
Biological application:
flux=−P(c2−c1)
(from Fick’s first law)
Where,
P: permeability
c2-c1: difference in concentration
Liquids:
Fick’s law is applicable for two miscible liquids when they are brought in contact and diffusion takes place at a macroscopic level.
Fabrication of semiconductor:
Diffusion equations from Fick’s law are used to fabricate integrated circuits.
Pharmaceutical application
Fick’s law is applied in medical science for the purposes of research and development in healthcare industries.
Applications in food industries.
Fick’s law also applied in food industries. Leaching and drying are normally controlled by internal diffusion.