PDMS membranes are very tricky. Peeling a thin one (30 um or less) of any substrate in air could result in stretching, tears, and membrane collapsing on itself (especially if it has large surface area). The best sacrificial layer for PDMS is PVA (poly-vinyl alcohol) solution in DI water. Spin it first (it will add couple nm to your wafer) and then spin PDMS. For membranes over 50 um, you can typically lift them of with tweezers without dissolving PVA. For membranes 30 um and less, I would submerge the wafer under DI water and gently peel membrane off while allowing PVA to be dissolved as you peel. The membrane will float on the surface without crumbling or folding. Additionally you could always bond a thick piece of PDMS to your membrane as a handle.

Unless it is required by your application, I would discourage use of organic solvents because they will permeate and swell your membrane like crazy.

What is the purpose? You want to have the cured film intact or the surface?

I want to spin coat a PDMS film that I can then peel off of the substrate and keep both the film and Si wafer intact. that way I might be able to reuse the wafer for when I want to spin coat another sample.

You will probably need an additional layer, something like carbon. Does that help? It should work for thin layers. I have some experience with cabron coated Si wafers used for SU-8 resist coating, and it works well. Surface roughness is also good.

Yes it does, thank you. Actual I used a polystyrene petri dish rather than going through the trouble and it seems to work for the application that I need it for. The roughness of it is pretty low and there is low adhesion.

Good idea! :)

Can anyone suggest the way of spin coating of aquous solution based quantum dots on thin film of TiO2?

Might I suggest another option? It may be possible to deposit a soluble layer (which is soluble in a solvent which your layer is not) - such as NaCl, and place it in the appropriate solvent, i.e. water to remove the layer. If you were able to use a NaCl or alternative soluble substrate you would be easily able to remove the film.

Any particular reason you must use Si substrate?

The roughness of a polished Si wafer is in the angstrom, and so I would be able to produce a thin and seemingly smooth film.

Perhaps one option is to add a sacrificial layer under the Sylgard. I don't know what this is....is it dissolved in nonpolar solvent? Anyway, if Sylgard is not water soluble, add a layer of a water soluble polymer on the wafer before you spin coat the Sylgard. Then dip the thing in water and float the Sylgard layer off. If Sylgard is water soluble you will have to find the opposite situation...more difficult because the organic solvent you choose would have to be more dense than the Sylgard in order for it to float.

PDMS membranes are very tricky. Peeling a thin one (30 um or less) of any substrate in air could result in stretching, tears, and membrane collapsing on itself (especially if it has large surface area). The best sacrificial layer for PDMS is PVA (poly-vinyl alcohol) solution in DI water. Spin it first (it will add couple nm to your wafer) and then spin PDMS. For membranes over 50 um, you can typically lift them of with tweezers without dissolving PVA. For membranes 30 um and less, I would submerge the wafer under DI water and gently peel membrane off while allowing PVA to be dissolved as you peel. The membrane will float on the surface without crumbling or folding. Additionally you could always bond a thick piece of PDMS to your membrane as a handle.

Unless it is required by your application, I would discourage use of organic solvents because they will permeate and swell your membrane like crazy.