Influence of direct fluorination treatment on surface and optical properties of colorless and transparent polyimides

Due to excellent comprehensive performance, colorless and transparent polyimide (CPI) films are the greatest potential substrates for flexible displays, lighting, and solar cells. In this work, CPI films were modified by direct fluorination to increase the wettability and transmittance. The effects of fluorination duration on the chemical structure and surface physical morphology of CPI films were investigated in detail by attenuated total reflection infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results show that, depending on the fluorination duration, direct fluorination causes significant changes in surface composition and structure. The F/C and O/C ratios of the samples were enhanced as the fluorination time increased. Surface microcrack increased at initially, then decreased as fluorination time increased. The fluorinated surfaces exhibit a high hydrophily and lipophobicity, and consequently a very high surface energy, according to contact angle measurements. In comparison to original CPI film, the fluorinated CPI films exhibited higher optical transmittance in the ultraviolet–visible light region compared with original CPI film. In addition, the fluorinated CPI films showed good thermal stability up to 500 °C and higher glass transition temperatures (Tg) compared with original CPI film.