Solid-phase molecular self-assembly facilitated supramolecular films with alternative hydrophobic/hydrophilic domains for skin moisture detection

Human skin moisture is closely related to health and personal care issues. Many creams were developed to claim capable of skin moisturizing. However, people can hardly check their skin moisture status and the moisturizing effect of various creams conveniently, since currently all the skin moisturizing detection rely on large equipment requiring power supply. Herein, we report a power-supply independent supramolecular film that is able to directly report the moisturizing status of the skin. With the strategy of solid-phase molecular self-assembly (SPMSA), the aqueous precipitates formed by commercially available polyelectrolyte and oppositely charged surfactant would transform into a supramolecular film under a mild mechanical pressure, where the hydrophobic surfactant domains bridged by polyelectrolyte merge into hydrophobic mesophases to reduce interfacial energy. The hydrophobic mesophase will greatly retard water diffusion inside the film, so that a humidity gradient is generated as the film is exposed to a humid environment. The film will bend upward automatically in touch with moisture skin, and the bending degree is proportional to the skin moisture status. Therefore, the film can be used as portable smart power-free skin moisture sensor.