I was trying to electrospun a nano-fiber sheet used as electrode. The material I used is 14wt% PAN (150,000 MW) solution (solvent: DMF). The PAN solution was electrospun directly onto a Nickel substrate (Fig 1). After electrospining, this sample undergoes following heat treatments.
1. 240 degree C in muffle furnace for 2 hrs. Heat rate 1 deg C/min. Air atmosphere. To make the PAN from a thermoplastic to a thermoset material. (Fig 2)
2. 900 degree C in tube furnace for 1 hr. Heat rate 5 deg C/min. Argon atmosphere. To carbonize the PAN and make it electroconductive.
However, after the carbonization process, the PAN sheet shows a severe deformation(Fig 3). Looks like it is shrunken. And the Ni substrate bent. (Fig 4)
I was trying to make the PAN sheet covering the Ni substrate entirely after carbonization. Anyone knows the reason for the deformation of PAN sheet? Any suggestion on how to modify the process?
Thank you!
Dear Siyuan Wu ,
Shrinkage and bending of PAM nanofibers can occur if they are not fixed during the temperature treatment and this problem can be solved by electrospinning it on aluminum foils as substrates and stabilizing the whole composite. In this way, the forces that would cause the nanofiber mats to break are distributed over the entire surface, making stabilization possible without fiber deformation.
I attached the related article, which has proposed this method for solving the shrinkage problems of PAN nanofibers.
Hope you find this answer helpful for your task.
The reason for the deformation is internal tension within the nanofibers. The polymers get stretched during electrospinning and when the solvent rapidly evaporates the polymers remain in a configuration with low entropy/high order. When you heat the polymers they can move relative to eachother and coil to reduce entropy. This causes shrinkage and deformation.
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