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Conductive paint by conventional technique using gum and graphite powder does not stick to the PDMS surface and comes off once the paint dries. How else can I make a conductive connection over the PDMS surface so that it can stick to it nicely?

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    $\begingroup$ Assuming that by PDMS you mean silicones, you might try an electrically conductive silicone adhesive, usually silver filled, because the only thing that sticks to silicone is silicone ;-) For really good long term bonding to silicones you might also have to plasma etch the PDMS surface for the best adhesion. $\endgroup$ Apr 26 '16 at 23:05
  • $\begingroup$ I do not want to introduce active electrochemistry of the silver as I want to study the electronic properties of my sample which is placed over the Poly-di-methyl-siloxane (PDMS). Hence I require something that shows sluggish re-activity. Graphite powder ink can meet my need but it is not sticking to the surface of PDMS $\endgroup$
    – RThakur
    Apr 28 '16 at 3:51
  • $\begingroup$ The bottom line is that only a silicone based polymer will stick to a silicone substrate. That said, you might want to make your own conductive adhesive by mixing the graphite powder into a silicone adhesive to make it conductive and then just apply it to the PDMS $\endgroup$ Apr 28 '16 at 12:55
  • $\begingroup$ I would first try Sil-Poxy adhesive sold by Smooth-On Corporation. This stuff is made to stick to silicones. Mix the graphite powder right into this adhesive , you will have to experiment to get the right conductivity for the cured layer . $\endgroup$ Apr 28 '16 at 13:20
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As you asked both, "How to make a conductive paint over PDMS?", and, "How else can I make a conductive connection over the PDMS surface so that it can stick to it nicely?", I will answer the latter question as your 'conductive paint' has been problematic for this application and there are already well established methods for conductive coatings for this particular material.

One option is sputtering. Sputtering is a technique that is widely available and is a fairly inexpensive process for coating materials such as PDMS. Sputtered films also have an advantage over other coatings (such as your gum paint), in that these films typically have strong adhesion to the surface being coated and it is a non-destructive technique (e.g. it works well enough to be used in electron microscopy).

Au, along with a host of other metals, are available for coatings, and they can be laid down in various thicknesses at rates from 10's to 1000's of nanometers per minute. In addition, this has been done many times before with this material and can give you the conductive surface you are looking for.

Here is a wasp we coated awhile back for the microscopy labs:

The Au has a resistivity of a few ohms across the wasp, and could be reduced further with a thicker coating and a more uniform surface

The Au has a resistivity of a less than 2 ohms across the wasp, and could be sharply reduced with a thicker coating and a more uniform sample surface.

Considering you have been painting the PDMS surface, I am inclined to assume minimal damage to the micro-structures is not an issue as is sometimes caused by this process.

A second, and potentially easier option, is to simply use an Au, Ag or other conductive foil, although it is difficult to say if this is a good direction for your project as we have few details.

Hope this helps!

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