Polymer-Water Interaction Enabled Intelligent Moisture Regulation in Hydrogels.

The water-vapor transition is critical for hydrogels in a collection of applications. However, how the polymer-water interaction along with the nature of the structure affect the macroscopic water-vapor transition remains a challenging question to answer. In this work, we tested the moisture transfer behaviors of a series of hydrogels at different humidities and found some hydrogels capable of lowering their surface vapor pressure to stop dehydration at low humidity and absorbing water from ambient air to recover toward initial states at high humidity. Through molecular dynamic simulations, we demonstrate that water inside these hydrogels undergoes increasing intensive intermolecular bonding during evaporation. The increased intermolecular bonding reduces the vapor pressure of the hydrogels and leads to the self-regulation. More interestingly, we demonstrate the self-regulation is closely related to the Young's modulus of hydrogels. These results provide further insight into the mechanism of the water-vapor transition in hydrogels and show potential in a broad range of future applications.