If you do not mind producing a thick film, say tens of micrometers, then you can apply extremely thin layer of mold release agent on a glass and coat this with the nano composite. This does have danger of contaminating the composite if the release agent is thick. Better approach is to treat the glass surface with near monomolecular layer equivalent of aliphatic silane coupling agent (ultra-dilute toluene solution of less than 0.1% silane and reflux overnight, followed by pure solvent wash). This will produce unreactive glass surface to which the composite film can be cast. Upon polymerization of epoxy, you can place the sample under warm water for sometime, a day or two, the film will be released without much effort. If you want to produce an extremely thin composite film, such as less than a micrometer, you can cast the composite on a salt plate, such as NaCl plate used for infrared spectroscopy. You can place the solution on the salt plate with the pure solvent placed nearby and put a cap to include the salt plate and solvent so that the closed space will be under near saturation of the evaporating solvent. This approach will allow extremely homogeneous thick sample. Another approach is to spin coat if you have spin coater. Upon polymerization, the sample can be placed in water to dissolve the salt place and the ultra thin film will float at the surface of water. You can then recover the film with copper grid for microscopy work.

If you do not mind producing a thick film, say tens of micrometers, then you can apply extremely thin layer of mold release agent on a glass and coat this with the nano composite. This does have danger of contaminating the composite if the release agent is thick. Better approach is to treat the glass surface with near monomolecular layer equivalent of aliphatic silane coupling agent (ultra-dilute toluene solution of less than 0.1% silane and reflux overnight, followed by pure solvent wash). This will produce unreactive glass surface to which the composite film can be cast. Upon polymerization of epoxy, you can place the sample under warm water for sometime, a day or two, the film will be released without much effort. If you want to produce an extremely thin composite film, such as less than a micrometer, you can cast the composite on a salt plate, such as NaCl plate used for infrared spectroscopy. You can place the solution on the salt plate with the pure solvent placed nearby and put a cap to include the salt plate and solvent so that the closed space will be under near saturation of the evaporating solvent. This approach will allow extremely homogeneous thick sample. Another approach is to spin coat if you have spin coater. Upon polymerization, the sample can be placed in water to dissolve the salt place and the ultra thin film will float at the surface of water. You can then recover the film with copper grid for microscopy work.

@Hatsuo. I don't mind having a thick layer, so I will go with your first answer. If I have any clarification I will get back to you in this thread if you don't mind. Thank you very much.

you could apply a defined thickness with a bar coater on a teflon or polyethylene sheet. After curing the film will not stick to these types of plastic substrates.

Apply a layer of stripper to the mold, then a thin layer of epoxy, or try a vertical placement