Dear Sadeghi,

COMSOL material library have the inbuilt properties of of PDMS (MEMS>>Polymers>>PDMS). So, you don't need to add the permeability values. Additionally, you can also define the material properties using the blank material.

Now look at your definitions:

1 barrer= 10^(-10) (cm^3. cm)/(cm^2.s.cmHg)

1 barrer=7.6×10^(-9) (cm^3. cm)/(cm^2.s. atm)

Since, 1 cmHg = 76 atm

This is implemented in your second row from first row directly. This implies that you can directly use the definition of 1 m= 100 cm.

I hope this will help you.

I would define a parameter with the units I like and use it.

For example my_unit_energy = 1 [kgxm^2m/s^2].