Formation of Turmeric-Based Thin Films: Universal, Transparent Coatings

Curry stains on clothes and dishes in daily life inspired us to investigate the potential use of turmeric powder, the major ingredient in curry, as a universal coating material. After condition optimization, the coating solution was made by boiling and filtering a turmeric slurry, and the coating was formed at pH 3, leading to the formation of ultrathin, transparent films. Various inorganic and polymeric substrates were successfully coated with turmeric-based materials, including gold, TiO₂, SiO₂, glass, stainless steel, indium tin oxide, nylon, polyethylene, polycarbonate, polypropylene, acryl, and poly(ethylene terephthalate). The turmeric-based coating was also applied to poly(tetrafluoroethylene) (PTFE, Teflon) and cyclic olefin copolymer (COC), and after double dip-coating, the water contact angle was changed from 118.2° to 49.1° for PTFE and from 91.2° to 44.7° for COC. The water contact angles for the other substrates converged to 35° after coating, confirming the substrate-independent universal coating capability of turmeric. The X-ray photoelectron spectroscopic analysis indicated the presence of nitrogen in the film, and the possible involvement of amines in film formation was investigated with several amine compounds.