Covalent cross-linking of PEI-HDI to construct superhydrophilic surface of PET film

Developing robust and durable superhydrophilic surfaces on polyethylene terephthalate (PET) films is critical for advancing their applications in self-cleaning and biomedical technologies. In this study, a coating solution containing polyethyleneimine and HDI polyisocyanate was bar-coated onto PET film surfaces and subsequently cross-linked to form a dense R-NH-CO-NH-R' covalent network. After modification, the PET film surfaces demonstrated superhydrophilicity (WCA=0°) accompanied by a significant increase in surface energy to 79.4 mN/m, while achieving excellent 5B-grade adhesion. Furthermore, when exposed to 40-hour immersion in aqueous solutions, the modified surfaces maintained their superhydrophilicity (0° WCA) with essentially unchanged surface energies. The coatings showed near-complete surface coverage along with substantial covalent bonds retention. Such crosslinking construction approach via bar-coating exhibits promising potential for PET films in superhydrophilic applications.