ok, i will try to pouring new pdms ad let you know about the result.

I din't try to use toluene but pentane: the pdms is still there.

thank you to all for the ideas :)

2009/11/19 Dirk Renckens - TNW :
> Dear Gareth and Emanuele,
>
> If you cure PDMS at the recommended temperature of 68 C, it forms a
> monolithic (one piece) structure with older PDMS. You could try
> resilanising the wafer and pouring new PDMS to strip the PDMS that
> remains. If you try it, could you let me know how it works out? Thanks.
>
> Regarding Toluene, in my experience this does not swell strongly enough
> to remove small (<3 mm) pieces of PDMS. However, as gareth says, it is
> okay with SU-8, so feel free to try.
>
> Good luck!
>
> Dirk Renckens
> Chem Eng PhD candidate TU Delft