Effects of the Hydration States of Water Molecules on the Mechanical Properties of Dual Movable Cross-Linked Polymeric Gels

Hydrogels are widely studied in basic science and applications under aqueous conditions. The material properties of the hydrogels are significantly influenced by the water content. As the water content increases, the hydrogels become more brittle. However, the precise relationship between the hydration state and the mechanical properties remains unclear. Intermediate water (IMW), which refers to absorbed water, plays a crucial role in influencing the biocompatibility and antifouling properties of these materials. In this study, the correlation between IMW and the mechanical properties of hydrogel was investigated by using dual movable cross-network (DC) gels. The DC gels feature knitted structures combining hydrophilic and hydrophobic polymers to regulate their hydration state. The mechanical properties of the DC gels generally decreased with an increasing amount of hydrophilic polymers due to the higher water content. Interestingly, certain compositions of the DC gels exhibited superior mechanical properties. Spectral, structural, and thermal analysis suggest that IMW contributes to cross-linking between polymer networks through hydrated water molecules, thereby enhancing the mechanical properties of the DC gels. This study highlights the critical role of water molecules in affecting the mechanical properties of the hydrogels. This study offers important insights into the interactions between polymers and water molecules, thereby contributing to the rational design of water-responsive functional materials.