I am trying to make a clear film of poly HEMA in THF, I make a viscous solution and let it evaporate for 5 days slowly but I don't know how to do the follow up from there to completely remove THF if I don't want to keep it for few more days? If I try to evaporate the solvent too fast the film will foam or have bubbles.
As stated above by Chithra, after casting the solution onto a PTFE-coated or silanized Petri dish (in order to ensure easy removal of the film), allow most of the solvent to slowly evaporate at room temperature until a solid film is formed. Then, put the dish in an oven and gradually raise the temperature up to 70-80 deg C, and keep it until no weight loss is observed. This technique allowed me to prepare smooth films of PHEMA and its copolymers.
Try to make a dilute solution say 3-5% w/v solution to keep the viscosity low. It may vary for your polymer. While making the polymer solution first donot shake the container (preferrably a volumetric flask) for 1-2 hours till polymer swells and dissolves. It takes some time for polymer to swell and any amount of shaking before that is only going to introduce bubbles and not dissolve it. Also make sure that your THF is dry as it absorbs water from air which may make the films hazy. You may ask any organic chemist to help you dry the THF and how to handle it for keeping it dry. Now with the lid closed gently stirr the flask by hand till the solution becomes homogeneous. Pour it in a petridish (may be siliconized). Once the film is reasonably dry (1-2 days) you can gently remove the film by pouring some distilled water (5-10 ml) (it is a non solvent) on top of the film in the petridish and use a thin needle to gently ditach the outer edges. Whole film may come out very nicely this way. Wash the film few times with distilled water to remove traces of THF from surface. Do this step only if your poymer in known not to interact with water and trap it. Now quicly dry the film by wrapping it between tissue papers. Now put the film preferrably in a vacuum oven between 60-80 degrees for 3-8 hours. This you may have to be standarize by trial and error which give best THF removal and no poymer degradation. At the end you may like to take a trial run on thermogravimetric analyzer and DSC to check if you get no weight loss before glass trasition (Tg) temperature. This way you may be able to get a desired optically clear thin film in about 2 days.
I missed to note the name of the poymer in my answere. It seems this poymer can absorb 60% water by weight. Hence any trace of water has to be avoided at all stages.
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