I need an inert sealant that is also a good thermal and electrical insulator. Suggestions?

Question

I am constructing a system using a standard Peltier component for use in a unique biomedical research application. I need to be able to seal the heat sink (cold side) of the Peltier component to improve its efficiency. The cold side will have a copper adaptor bonded to it and give rise to an insulated copper wire that pulls heat from the test system. I want to seal all the exposed copper on the cold side, so that only the wire insulation and sealant are exposed. The cold side of the component will be pulling about 0.5 W of Q and operating at about 5degC. The hot side will dump to forced convection and will not, obviously, be sealed. The sealant should be nontoxic, inexpensive, widely available, relatively easy to work with, and, above all, a good electrical and thermal insulator. It looks like the thermal conductivity of silicone and most epoxies are too high for my purposes. This is a little outside my area of expertise. Any suggestions?

@to_700mi: no, I'm not talking about the wires that run the peltier. We're using a large-bore copper wire as a heat conduit, to pull heat out of a biological system onto the cold side of the peltier. The cold side cools a film of copper foil soldered to copper wire, which leads to a copper adapter fitted to an artery. The Peltier cools the wire, the wire cools the adaptor, and the adaptor cools the artery. The hot side isn't bonded to anything; it's exposed to air and cooled by fan convection. We can do this because our Qc and deltaT are relatively small, and our prototype assembly demonstrates that we can maintain a robust thermal gradient over the required length of copper wire. But we want to improve the efficiency of the device by sealing the cold side with a thermal insulator so that it's not absorbing any heat from the environment.

Answer 1

I would look at foam polyurethane otherwise known as "Great Stuff"

Answer 2

A Peltier device is clamped between the surface to be cooled and a large heatsink

BOTH surfaces need heatsink compound
as much heat has to be transferred from the four surfaces involved, surface irregularities prevent this from happening

I do not understand your concern about the connecting wires, they are topologically not part of the cold part and not part of the heatsink , but reside in the space between the two

The device I used was fed with up to 4 Amps from 15 Volts
So a large fan was needed to increase heatsink efficiency

60 Watts input when you are trying to cool something down
is a real challenge AND the hot side is only about 3 mm from the cold side

Answer 3

Use GE XST silicone caulk.

It's about $5 a tube and ROCKS. I've had it on the outside of my house for about 10 years and the stuff adheres like hell and doesn't chip/blister or peel off.

Answer 4

For sealing between window frames `and studs you can get urethane foam in an aerosol can.

Answer 5

What about using a ceramic to seal everything. ceramic are low voltage and thermal conductors. Cement is even a type of ceramic and may work.

Answer 6

try scotchkote at the url below.

Answer 7

100% silicone sealer should work. You can buy at any hardware store.