Open Air Plasma Deposition of Superhydrophilic Titania Coatings

A method for the deposition and functionalization of a nanostructured organotitanate thin film, which imparts superhydrophilicity to a surface with a one-step, open-air process, is described. Extreme wetting ( < 5 degrees) is achieved through synergistic contributions from both nanoscale roughness, visible light absorption caused by nonmetal dopants, and oxygen vacancies and surface activation by reactive plasma species. To test the efficacy of this material as an antifog coating, glass is coated and subjected to aggressive changes in humidity. Under both fogging and defrosting conditions, the superhydrophilic coating achieves a high degree of transparency, showing nearly two orders of magnitude improvement over the bare glass. The measured adhesion of the superhydrophilic coating is 5.9 J m(-2), nearly double that of the solution-processed control. The reliability of the coating is further validated by demonstrating scratch-resistance. Additionally, the incorporation of organic matter into the molecular structure of the coating disrupts long-range crystallinity from developing. This structural and subsequent chemical analysis of the coating reveals that inorganic and organic species are intimately connected at the nanoscale via alkyl and alkoxy bridges. The amorphous organotitanate material is distinct from conventional TiO2, which requires high temperature crystallization and extensive UV irradiation to display similar superhydrophilic qualities.