Thermal conductivity of hydrogels with damaged network

The thermal conductivity of polymeric materials is greatly influenced by the morphology of the internal molecular networks. Specifically, the irreversible alteration of molecular networks through external stress or damage changes the thermal conductivity of polymers. However, the intricate relationship between molecular network alteration and changes in thermal conductivity under large deformations remains elusive. To elucidate and quantify the variation of thermal conductivity in hydrogels as a result of the damage of polymer networks, it is necessary to construct a physically-based model. In this work, taking the PAAm-PAAm double-network hydrogel as a model material, we utilized uniaxial tension to precisely modulate the damage levels of materials. Notably, experimental observations revealed a decrease in hydrogel's thermal conductivity concurrent with progressive structural damage. It was assumed that the inter-molecular heat transfer pathways were reduced due to damage of cross-linkers within the networks. Then a percolation model utilizing square site structures for capturing heat transfer pathways' influence on overall thermal conductivity was constructed. This work deepens our fundamental understanding of the interaction between damage-induced network alteration and the evolution of thermal conductivity. Moreover, the constructed model enables the prediction of changes in the thermal conductivity of hydrogels through simple mechanical testing.