Deposition of aromatic polyimide thin films in supercritical carbon dioxide

• Depositions of polyimide thin films on the substrates were carried out in scCO2.
• An apparatus including a cold-wall reactor was constructed for deposition in scCO2.
• ODA and PMDA were used as polyimide monomers.
• The film thickness increased with increasing supplying monomer concentrations.
• The film thickness decreased with increasing deposition temperature.

The deposition of aromatic polyimide (API) thin films was carried out in supercritical carbon dioxide (scCO2) with 20 mol% of N,N-dimethylformamide (DMF) as a cosolvent, and using 4,4′-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) as monomers. A new apparatus based on a flow method that consisted of a cold-wall type reactor and two supply lines for each of the API monomers was used. The effect on the morphology of the films was investigated at feeding monomer concentrations and deposition temperatures ranging from 5 × 10−4 to 5 × 10−6 on a mole fraction basis and from 423 to 523 K, respectively. The results showed that increasing the monomer concentration and decreasing the deposition temperature increased the thickness of the films, and a smooth surface of the film was obtained at 423 K. Additionally, FT-IR study and thermogravimetric (TG) analysis of the film deposited at monomer mole fractions of 5 × 10−5 and at a deposition temperature of 473 K were also carried out. The FT-IR spectrum of the deposited film in scCO2 with DMF represented imide structures although there was a small peak of amide carbonyl stretching that originated from the polyamic acid and DMF. The TG curve indicated the temperature of 5% weight loss was more than 800 K under an air atmosphere after complete imidization.

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