Re: Flexible membrane material between silicone oil and sea water

emiller wrote:
>
> A sensor we're designing requires a flexible membrane to separate sea
> water from silicone oil (polydimethylsiloxane). Can anybody recommend a
> *** material that can be bonded to a stainless steel substrate?

Glass is inert against sea water, and a microscope
cover slip is thin enough to be flexible.
Aquarium cement certainly would have good adhesion
to the glass, and probably to the stainless as well.
However, if it is a silicone adhesive, it might
lose adhesion in contact with the silicone oil.

Stainless steel shim stock is available as thin
as 0.001", which is quite flexible. However
stainless corrodes in contact with sea water.

Titanium might be a possibility, if thin sheets
are available. Checking on:
http://www.smallparts.com/products/descriptions/smti.cfm
I don't see anything thinner than 0.035",
which I don't think would be flexible at all.

I have a thin tantalum *** I bought on eBay,
which is somewhat flexible, but you probably
won't be able to find another one. This one
was made for the proverbial metal plate in
the head (to repair cranial injuries). I don't
think they repair heads that way anymore.

Polyimide, polyethylene, and polyethylene napthalate
are used as flexible printed circuit substrates,
which is a fairly demanding application.
Epoxy adhesives are often used to bond them
to copper foils.

Among plastics, beware of the possible effects
of water absorption. Kapton is about 4% water
at saturation. If you go with polyimide at all,
Upilex-S from Ube has much lower water absorption,
only about 1%.
.