In Situ All‐Weather Humidity Visualization by Using a Hydrophilic Sponge

Abstract Humidity visualization is of significant importance across both the living systems and the industrial processes, which remains a huge challenge. Herein, for the first time, a hydrophilic sponge, which is composed of rigid gel and super hygroscopic material, has been demonstrated capable of all‐weather humidity visualization in a portable, convenient, economical, and in situ manner. This promising aspect is attributed to the effective all‐weather humidity capture and various color display as a response to the humidity capture capacity, of the super hygroscopic material; as well as the rapid humidity transport and excellent humidity storage ability provided by the porous rigid gel. As a consequence, combined with a smartphone, the invisible information on the environment's relative humidity levels, on the one hand, can be correlated qualitatively with the specific color display of the sponge; on the other hand, it can be correlated quantitatively with the specific color intensity, providing a pretty good smart model for humidity visualization in various complex environments. The present humidity visualization technology may open up a new avenue for the development of novel humidity sensors with a wide range of practical applications.