You can try depositing something
like tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane to help release
the PDMS from the mould. This can be done quite easily in a
vacuum desiccator.

Your curing temperature is higher than I would normally use (65degC for 1
hour should be enough for Sylgard 184). Higher curing temperatures can cause
more shrinkage of the PDMS and maybe other effects (2:30hrs is far longer
than necessary at 120C).


On Sun, Dec 12, 2010 at 16:26, DEBASHIS MAJI  wrote:

> Dear all,
>
> I need to make some fine structures (rectangular ridges) over PDMS using
> SU8-50 as the master moulds over Glass substrates. I am able to peel off
> the
> PDMS with the ridge structures in the first trial with the SU8 master.
> However when I am trying to reuse the master again, Their is problem in
> peeling off of the PDMS and it tends to tear off at the ridge corners. In
> the process the Su8 also gets spoiled with the tweezers. My ridges vary
> from
> 500um to 1500um in width and are 50 um in height. I am using the same
> baking
> conditions for PDMS every time (120C for 2.30 hrs). I have also tried to
> increase the baking time for the second trial, but it still remains a
> problem. Is it some residual PDMS in the first trial that is creating
> problem for the 2nd run? Do I need to clean the SU8 masters every time
> after molding PDMS?... I shall be highly obliged if anybody can suggest
> some
> easy solution to this like applying some thin layer between the two layers
> before pouring PDMS over SU8... etc..
>
> Thanks in advance to all....
>
> Debashis Maji,