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Hey Engineering Community, a physicist this side.

I am tinkering on a project where I need a local deformation of the thin sheet(0.2mm thickness, 25cm*20cm dimension); pressing on the surface from one end will give me a local deformation in the z-direction.

So, to make ends meet, I used Liquid Silicone Rubber, but I want to make at least one surface conductive. Now, I have tried adding conductive materials like graphite and MnO2+Zn powder( from an AA battery cell), but the conductivity is not shown, probably because all the material is embedded inside the surface of LSR after curing.

So, what I did was to make a layer of LSR and before it dried up, I added MnO2+Zn mixture on it, and then after it dried up, I washed off the excess powder, the surface did become a bit conductive, giving around 10^3 ohm-cm resistivity. Now, it's not optimal; I need more, and I need a better method of actually doing it.

Now, I was thinking of somehow adding a thin layer of polypyrrole on silicone rubber, but I haven't found a paper doing this. What primer or adhesive should I use and how to do it? (Remember, I am not a material engg, so it might be something simple I am missing).

Ofcourse a technique to make the whole sheet conductive also works, but I don't want to compromise on the flexibility of the sheet, I need to rise at least 0.1mm above(deformation).

Also, one more problem I am facing is attaching electrodes to the rubber sheet as it is an insulator and attaching copper tape as electrodes need a conductive adhesive, but I tried making one using the MnO2+Zn mixture again with Fevicol Probound, and after drying the adhesive becomes non-conductive. (I don't want to use Silver Ink as electrodes as it becomes hard after drying)

Any suggestions would be appreciated.

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  • $\begingroup$ You can embed a conductor in silicone. Overlap for joints, etc. it will wear over time, but can't be too much worse than a motor's brushes. $\endgroup$
    – Abel
    Commented Jun 11 at 15:08
  • $\begingroup$ Consider using carbon or gold pills/pellets as are used in silicone rubber keypads. These are thin moulded silicone rubber sheets with keys incorporated. Used widely in (for example) TV remote controls. As an example, see this link to a manufacturer of this type of moulding pannam.com/rubber-keypads . From your description, I cannot be sure if it would be helpful, so take it as a suggestion. $\endgroup$
    – elchambro
    Commented Jun 12 at 1:08

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The classic method is to take a sample of the raw rubber and mill significant weight percents of carbon black into it, so as to form a network of carbon particles within it that are touching. Electrical contact is made by mechanically squeezing copper tape to the surface of the carbon-loaded polymer or by extruding the rubber over copper wires and then making your connection to the wires.

The hi-tech way is to put a sheet of the rubber into a vacuum deposition system and sputter or vapor deposit an atomistically thin carbon, aluminum, copper or gold layer onto its surface. The conductivity will depend sensitively on the thickness of the sputtered layer.

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There are several main methods of producing "electrically conductive" rubber.

One is to add fine particulate such as carbon to the rubber as you have been doing. A second method is to insert a metal structure- mesh or wires of a sort. These are mainly used for AC conductivity to deal with EMF, but even the carbon particle variants can have low enough resistivity to pass DC (consider them a resistor rather than ideal conductor for voltage drop)

https://www.majr.com/conductive-rubber-what-it-is-and-where-its-used/

Have you considered purchasing some conductive rubber and working it into the geometry you require? Keep in mind that silicone rubber in excess of ~800 deg F might weld- you may need to inert the surroundings to preserve carbon in such rework.

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