I've been trying to make a solution with 20% wt. polystyrene (average molecular mass 192000) and 80% PGMEA. PGMEA did dissolve PS, but the problem is, there are particles that no matter how many days I stir the solution, they remain as particles. Furthermore, the solution looks a bit cloudy (another sign of having more particles). And finally, solution looks like gel, and not like a viscous solution.
Any thoughts on how I can fully dissolve PS in PGMEA is highly appreciated.
What type of polystyrene that are you using? The behavior you are observing occurs in smaller concentrations?
This behavior can be observed in crosslinked materials, in HIPS and in mixtures.
I use a pellet type polystyrene. not sure about the grade or purity. the only info given by Sigma-Aldrich is theaverage molecular mass. here is the URL of the product I used:
http://www.sigmaaldrich.com/catalog/product/aldrich/430102?lang=en®ion=US
I use SU8 developer (PGMEA), magnetic stir and elevated (90 C) temperature to mix it. when the solution cools down, it becomes cloudy. without magnetic agitation, insoluble particles were too big that I could even see them with naked eyes.
Initially I tired Toluene with the same result, and switched to PGMEA due to its lower vapor pressure and higher boiling point. As long as the solvent has relatively low vapor pressure, which gives me a bit of time to make a uniform film via spin coating, I can change the solvent. other reason to choose PGMEA was that I noticed it is the solvent used in many photoresists.
I prefer NOT to dilute it as I would like to obtain a relatively thick (5-10 microns) film via spin coating.
Thanks again for your help!
Since it is cloudy in Toluene then it is not pure linear polystyrene.
You'll have to change the grade. Contact a polystyrene supplier and get samples of injection molding grades with various melt flow rates. You'll have to figure out the Mw and the type of additives they may be utilizing.
thanks everyone for valuable answers. I still have no clues how to dissolve the rest of the materials in the PGMEA. are there any ways to filter out residuals? or even after filtration, aggregation at room temperature might occur? I tried paper filter and gravity based filtration, but the solution is very viscous and not even a single drop passed from it.
No. Just need to use a grade with tg above 100C and a solvent with low vapor pressure.
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