In Situ H₂O Meter by Visualization in Hydrogels

The solvent content strongly affects the viscoelastic properties and network structure of hydrogels. Because of the gels' structural susceptibility and autofluorescence background, there is still no visual method to evaluate the water content in micropores. Herein, a colorimetric molecular probe (DHBYD) was synthesized for in situ visualization of water content in the micropores of hydrogels. The rapid and reversible colorimetric responses of DHBYD to solvents were obtained, which resulted a full linearity range (0 to 100%) for detecting water content in real time. Demonstrated by theoretical calculations, the sensing was attributed to changes in intramolecular charge transfer via deprotonation of phenol group. A cubic polynomial, on correlation of RGB values with water content, was established for real detection of water content in hydrogels. It reveals a new pathway for simple, in situ, and full-range evaluation of solvent content in micropores of hydrogels without any complicated procedures or expensive instruments. This would achieve fast and in situ monitoring of hydrogels to improve gel properties for better applications. It can be extended to evaluate the solvent content in other fields such as synthesis and industrial applications.