Dear Roaa,

Nanoparticles of zero valent metals (less than 5 nm) size have been suggested as superior alternatives to superparamagnetic metal oxides, having greater superspin magnitudes and lower levels of magnetic disorder. But the synthesizes of such particles have been hindered by their instability.

It has been stated that pore wall volume has a significant effect on the dynamics of such nanoparticles.

You may want to look at Fick's law and 2D diffusion.  For example:

 August 13th, 2015 The importance of the measurement of diffusion in 2-phase systems

https://www.brainshark.com/malvern/vu?pi=65736585&b=1&tx=120486&c1=22

Thank you for your information dear Gowhar.

Dr. Alan Rawle, am realy happy that you sharing this, it was very helpfull.