Hydrophillic coating on silicone

[Silverbullet]

I have a large number of silicone mouldings which are absorbing too much water. The problem was due to using a silicone filled with precipitated silica rather than fumed silica. Precipitated silica absorbs up to 8% water whereas the fumed silica absorbs only 1.5%. I have tried drying the mouldings and painting with activated Silicone oil to reduce absorbtion but this did not work. Does anybody know of a coating or process which could reduce the water absorbtion

 

[Silverbullet]

I have been advised that I might try impregnating the surface with a hydrophillic wax as this might occupy the water absorbtion sites. Does anybody know about these.

 

[btrueblood]

Um. I think you mean you want a hydrophobic coating, i.e. a coating which repels, or does not absorb, water.

Silicone oil is one of the most water-repellent substances around, but probably acts as a semi-solvent to your cured silicone rubber.

 

[Silverbullet]

Yes. I do need a hydrophobic surface. My advice was to use a surficant which would attach its hydrophillic side to the silica filler and therefore present a hydrophobic surface. I am not happy with the results so far and I prefer the silicone oil solution. I have only tried one type of silicone oil. Are there many different oils and might one have significantly improved results over another.