Effect of Embedded g-C3N4 Nanosheets on the Hydration and Thermal Response Behavior of Cross-Linked Thermoresponsive Copolymer Films

The effect of embedded graphitic carbon nitride (g-C₃N₄) nanosheets on hydration and thermal response behavior of cross-linked thermoresponsive poly(di(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate), abbreviated as P(MA-co-MA₃₀₀), thin films is probed by white light interferometry. Compared with that of the cross-linked pure P(MA-co-MA₃₀₀) films, the surface roughness of the cross-linked hybrid films is slightly increased, which is caused by the minor aggregation of g-C₃N₄ nanosheets during the spin-coating process. After exposure to a water vapor atmosphere, both cross-linked pure and hybrid films can absorb water and swell. However, the introduction of g-C₃N₄ not only induces a larger hydration extent but also triggers a nonlinear transition behavior upon heating. This prominent difference might be related to the residual hydrophilic groups (-NH₂ and N-H) on the surface of g-C₃N₄ nanosheets, which enhance the interaction and absorption capability for water molecules in the hybrid films. Upon further increasing the amount of embedded g-C₃N₄ nanosheets in films, more hydrogen bonds are formed and a larger hydration extent of films is observed. To break all of the hydrogen bonds in films, a higher transition temperature (TT) is required. The observed hydration and transition behaviors of hybrid films can be used to design hydrogel-based films for hydrogen evolution or wastewater treatment.