Dear Muralishwara Kakunje, these phenomena though are interrelated, they present a broad complexity related to the assumptions under which the derivations are performed. The first link is a similar question thread discussed on RG, they others are support documents, hope they will be usefull. My Regards

https://www.researchgate.net/post/What_is_the_difference_between_permeability_and_diffusion

https://doi.org/10.1063/1.5036999

https://doi.org/10.1557/PROC-137-179

Dear Muralishwara Kakunje, these phenomena though are interrelated, they present a broad complexity related to the assumptions under which the derivations are performed. The first link is a similar question thread discussed on RG, they others are support documents, hope they will be usefull. My Regards

https://www.researchgate.net/post/What_is_the_difference_between_permeability_and_diffusion

https://doi.org/10.1063/1.5036999

https://doi.org/10.1557/PROC-137-179

Dear Dr. Muralishwara Kakunje ,

to reinforce the interesting answer of Dr. Abdelkader BOUAZIZ , I would like to suggest you also to have a look at the following paper:

-An Indirect Approach for Correlation of Permeability and Diffusion Coefficients

K.K. Al-Tarawneh, O. Buzzi, b, K. Krabbenhøft, A.V. Lyamin, and S.W. Sloan

Defect and Diffusion Forum, Vols. 283-286 pp 504-514 (2009)

Available at: https://www.newcastle.edu.au/__data/assets/pdf_file/0020/23267/26_An-Indirect-Approach-for-Correlation.pdf

Best regards, Pierluigi Traverso.

The concept of diffusivity has different interpretations: the ability to diffuse transfer (diffusion capacity\diffusion ability), diffusion coefficient\diffusion constant.

If the term refers to the transfer of a substance, then this is the process of mutual penetration of molecules or atoms of one substance between molecules or atoms of another substance, leading to a spontaneous alignment of their concentrations throughout the occupied volume. For example, according to Wikipedia, "Diffusivity, mass diffusivity or diffusion coefficient is a proportionality constant between the molar flux due to molecular diffusion and the gradient in the concentration of the species (or the driving force for diffusion). Diffusivity is encountered in Fick's law and numerous other equations of physical chemistry".

The term in a more General sense can also refer to other physical (chemical, etc.) phenomena, for example, the coefficient of thermal conductivity or thermal\temperature conductivity coefficient. Or it can describe transport processes in systems of different nature, such as the diffusion of charge carriers or magnetic moment.

The word permeability also occurs in different areas. So, according to Wikipedia (https://en.wikipedia.org/wiki/Permeability):

"Chemistry:

Semipermeable membrane, a membrane which will allow certain molecules or ions to pass through it by diffusion [this describes the property of penetration, passing through the barrier by the diffusion process - ATM];

Vascular permeability, the movement of fluids and molecules between the vascular and extravascular compartments;

Permeation of a gas or vapor through a solid substance.

Earth and soil science:

Permeability (earth sciences), a measure of the ability of a material (such as rocks) to transmit fluids

Permeability (foundry sand), a test of the venting characteristics of a rammed foundry sand

Hydraulic conductivity, the permeability of soil for water"

But perhaps the most widely used term is in Electromagnetism:

"Permeability (electromagnetism), the degree of magnetization of a material in response to a magnetic field", i.e. in magnetism and magnetic materials science, it means the ability of a substance to magnetize and "amplify" the applied external magnetic field. This is the coefficient of proportionality between the magnetic field strength H and the magnetic induction B in the substance (mu). In the Gaussian system of electromagnetic units, this is described by the ratio B = mu*H.

But as we can see from the previous answer, even in a narrower area of your interests, there can be broad interpretations of phenomena and concepts associated with these terms.

Hi;

The term permeation describes the overall mass transport of the gas or liquid penetrant through the composite material, while the term diffusion describes the movement of the penetrant molecules within the mass of the material. Generally, molecular diffusion through the composite material is the slowest step and therefore the determining speed in the permeation process.

With my best regards

Dear Muralishwara Kakunje;

Please find attached some interesting articles explaining the difference between permeability and diffusivity which I hope you find useful.

With my best regards

Please find some articles explaining the difference between permeability and diffusivity :

Relationship between permeability and diffusivity in polyethylene glycol hydrogels

Article Relationship between permeability and diffusivity in polyeth...

Diffusion and Permeability

https://doi.org/10.1016/B978-012656976-6/50105-0

Relationship between permeability and diffusivity in polyethylene glycol hydrogels

G S Offeddu , E Axpe , B A C Harley , M L Oyen

Thanks everyone for joining the discussion. There are lots to learn. Thanks for the attachments.

Dear Muralishwara Kakunje;

To be concise, permeability is the product of diffusivity and solubility.