The property of diffusion that is concerned with the construction materials is an essential knowledge that has to be identified, in order to understand the sustainability of civil engineering structures. The diffusion here is defined as the transportation process that is carried out at the molecular level by the component in a given medium. This transportation is caused due to strong agitation it is subjected to. This is motion or vibration is called as Brownian motion. In a thermal aspect, we can call it as a vibrational effect.
The principle is that a difference in concentration within a medium would facilitate in a motion. The motion will happen from the point of higher concentration to lower concentration area. Even in the fluid that doesn't move in naked eye show the diffusion process at the molecular level. Here as per our discussion, the fluid considered is water.
The phenomenon of diffusion is irreversible. The overall particle motion is designated as a concentration change locally, which is represented by C. This is because the motion of each ion in the solution is difficult to be studied. The ion in the solution is designated by its chemical potential, which is represented as ς. Where the relation is given by
ς = ςo + RT (lnC)
The reference state chemical potential value is given by ςo, T is the absolute temperature, R is the gas constant and C is the concentration.
A flow of J⃗ vector ( a component) is caused due to the chemical gradient. When we understand from the thermodynamics of the irreversible diffusion process carried out, it is clear that the flow and the chemical potential have a linear relationship to each other.