How can overcome delamination problem on multilayer chitosan solutions (containing 1 % chitosan (wt/v) in 1 % (v/v) acetic acid)?

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Raul Montes

Looking at your images, I am pretty sure you have a contamination problem. But there could be a variety of reasons, probably a combination of the following:

Substrate Contamination: To achieve good adhesion it is necessary to remove organic residues and particulate contaminates from the substrate. Try using different cleaning processes. I will at least use AMI (acetone->methanol->IPA) ultrasonic baths or RCA-1 cleaning (5:1:1 H20:HCl:H202). You can also try piranha (3:1 H2SO4:H2O2). Make sure to follow the proper safety precautions. Measuring contact angle can provide immediate quantitative insights into surface cleanliness.

Solvent contamination: It is also possible that the contamination is coming from other sources such as the solvent, which usually results in streaks in the film. To solve this you can filter your spin coating material, for example, using a syringe filter.

Bad adhesion of the first layer: It could be the case that you have good adhesion between subsequent layers but bad adhesion of the first layer. I suggest using O2 plasma to activate the surface. In some cases using a longer contact time for the first layer creates a better anchoring network for the subsequent layers. This is especially helpful when using solvents with low evaporation rates.

Bad interlayer adhesion: If you are depositing the same materials, notice that the underlying film is soluble in the spin coating solution, therefore make sure to use a proper drying step after each deposition. You can try using temperature or a vacuum desiccator. A vacuum oven at a relatively low temperature (40-60C) usually gives good results.

Too high acceleration: too high velocities or accelerations create excessive turbulence. You are using relatively low velocities, so try to lower the acceleration as the speed goes from 500 to 1000 RPM.

I suggest going over the following guide:

https://www.ossila.com/en-us/pages/spin-coating

Desmond Ang

Dear Nafi,

Besides the common contamination issue from a multiple-processing coating approach..

Environmental cleanliness, could attribute to the delamination issues, which you might want to consider as a controlled items in designing processes..

Good luck, Cheers!

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