[mattfred]

I need to measure the dielectric constant of several molecules. I have tried to make a parallel plate capacitor and determine the capacitance from the time constant (tau = rc). My time constants seem to be on the order of 50 ms even with 20 kOhm resistor in place. The plates are approximately 225 cm^2 of polished aluminum approximately 0.25 cm apart. My current seems way lower than it should be (~50 nA) initially and the capacitor seems fully charged in under 0.5 s. I'm applying 210 V with an instrument that should have time resolution under 5 ms and sub-femptoamp precision.

Do I just need higher voltages? There are commercial devices with similar design and functionality that cost several thousand dollars that I don't have available. The source meter should be plenty accurate for this task though.

Any help with this problem (even suggestions of other ways to determine relative dielectric strength) would be greatly appreciated. Let me know if there are more details that you need.

Thanks.