Covalently Modulated and Transiently Visible Writing: Rational Association of Two Extremes of Water Wettabilities

Anticounterfeiting measures are of ever-increasing importance in society, e.g., for securing the authenticity of and the proof of origin for medical drugs. Here, an arms race of counterfeiters and valid manufacturers is taking place, resulting in the need of hard-to-forget, yet easy-to-read out marks. Anticounterfeiting measures based on micropatterns—while being attractive for their need in not widely available printing methods while still being easily read out with fairly common basic optical equipment—are often limited by being too easy to be destroyed by wear or handling. Here, nature-inspired wettability is rationally exploited for developing an unprecedented anticounterfeiting method, where hidden information can be only identified under direct exposures to an aqueous phase or mist and disappears again on air-drying the interface. A chemically reactive and hierarchically featured dip coating, capable of spatially selective covalent modification with primary amine containing small molecules, is devel...