Self-healing materials have shown great promise in recent years with improvements in mechanical robustness and healing ability. Still, there is great work to be done in understanding how these materials deform under strain on a molecular level.  In this work, we have demonstrated a tunable self-healing elastomer with both dynamic and covalent crosslinks using two sequential amide condensation steps from a fatty acid starting material.  This modular synthetic strategy allows for controllable changes in materials properties through variations in the structure and concentration of reagents.  The elastomer was able to be stretched over 500% and could regain up to 50% of its toughness after healing at room temperature.  The Young's Modulus of the elastomer varied between 0.35 and 2.1 MPa, depending on reaction conditions. Using this material as a platform, we studied the mechanism for stress dissipation in the hybrid elastic network under strain.  With infrared spectroscopy we were able to monitor the �open� or �closed� state of the hydrogen bonds via shifts in the N-H bending frequency of the amide hydrogen bonding groups.  As the material was strained, the peak for N-H bending shifted to show an increase in �open� hydrogen bonds after about 100% stain.  This shows that hydrogen bonds begin to break after a critical strain and they fail before the covalent crosslinks.  This work supports the idea that the dynamic crosslinks begin to reversibly break before the covalent crosslinks in this and other hybrid network systems. It also shows that dynamic crosslinks are an effective means of stress dissipation when used in concert with covalent crosslinks.

Stress dissipation via hydrogen bonding in a hybrid network self-healing elastomer

248th National Meeting (2014)

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