Constant thickness for cast polymer

[simin44]

I need to cast my Eudragit (Polyacrylate) copolymer for NIR spectroscopy. Critical point: I need very constant thickness in all part of the cast. I tried several times using PTFE casting dish. It seems as the polymer is drying (at room temperature) the middle part of the cast become thicker than the edge of the cast. Is there any technique to prevent it?

 

[anthamatten]

This is always a challenge. I'd try a few things: using a larger casting surface (to remove edge effects), changing solvents (I don't know what you're casting from), and using a so-called doctor's blade to level your solution immediately after casting. You might want to try dip coating too, if you have a motor, or something to pull the substrate out of a solution at a constant speed.

 

[simin44]

Well, I need to cast the polymer since I have to cut to the pieces and scan them later using Near Infrared Specs. NIRS technique is very thickness sensitive, even a difference of 1 micrometer is significant. Dip coating would not be an option since I need to cut and remove the film for farther curing analysis. The solvent is water and solid content of the polymer mix is 10%. Pretty dilute. I appreciate your input. thanks a lot,