Simulating electrical double layer in comsol

Hi,

I am trying to simulate an ISFET. There are two electrical double layers in the device. One is at the electrolyte insulator interface. The second one is at electrolyte electrode interface. So, how can they be simulated individually and as a complete set? Finally, i want to couple this model with a mosfet with the insulator at the gate. How shall i proceed?

Regards,
Soumendu