I have been trying to spin coat alternating layers of PVP (polyvinylpyrrolidone) and PS (polystyrene) polymers on glass substrate. I would start by coating PVP on glass first and then the second layer would be PS, these two layers on visual inspection is good but when i try to coat third layer of polymer i.e PVP it gets crack and appearance of film is frosty.
solvent for PS - toluene
solvent for PVP - ethanol/Acetonitrile(50/50 wt %)
Also, concentration of polymers in solvent which i had tried spin coating is 1,2,4% by wt but having same issue.
Thank you.
Dear Pritam,
Have you annealed the layer After your coated film? It may help if you anneal each layer at the temperature above the boiling point of each solvent you used.
Dear Xuhua, thank you for response.
yes we have tried annealing but still having same problem of cracking.
Dear Pritam,
The molecular weights (MWs) of your PVP and PS polymers can play an important role for your spin-coating film quality. Tring varied
MWs of polymers may solve your problem.
Best wishes
Xuhua
Dear Xuhua,
How molecular weight affects the film quality?
we used PS(Mw=35000) and PVP(Mw=40000)
Dear Pritam,
It is well known that the solvent and molecular weight of a polymer have a big influence on spun polymer thin film quality due to the flexibility of chains. Please see below reference:
https://onlinelibrary.wiley.com/doi/abs/10.1002/pen.760301104
You may try to use certain ratio of high and low molecular weight PS and PVP to optimise the film quality. At the meantime, there is another factor of varied solvents that you can optimise for the film quality.
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