Enhancing Self-Healing and Mechanical Robustness through Aluminum Acetylacetonate-Driven Metal-Ligand Coordination for Skin-Inspired Sensing

In the field of advanced materials science, the application of aluminum ions as dynamic metal salt cross-linkers in self-healing polymers has been less prevalent compared to transition or rare earth metal ions, attributable to the relatively modest self-healing and mechanical properties of aluminum ions. Our study introduces an alternative strategy by combining aluminum ions with acetylacetonates (acac^-) as counteranions and integrating a pyridine-capped polyurethane-urea polymer backbone (PTD) and phosphorus-rich small molecules (3N2AP) to develop a composition, Al_ac-3N2AP-PTD. This formulation exhibits phosphorus-based flame retardancy, improved self-healing capabilities, and enhanced mechanical properties. It demonstrates superior performance compared to existing aluminum-based systems and is competitive with traditional transition metal ion-based systems. To elucidate the underlying mechanisms of these enhancements, molecular dynamics (MD) simulations were conducted to examine the coordination dynamics and the effects of counteranions within the polymer network. The simulation results indicated longer coordination bond lengths in the system incorporating acac^-, supporting its efficacy and clarifying the mechanisms contributing to the increased self-healing capabilities and mechanical robustness. In our development of a stretchable, self-healing, and conductive composite, we fabricated PPy-Al_ac-0.25-3N2AP-PTD via an electrochemical deposition process. This material acts as an electronic skin (e-skin) strain sensor, exhibiting strain sensitivity while preserving its inherent mechanical and self-healing properties, thus differentiating it from traditional doping methods. The use of acac^- as dynamic counteranions in metal-coordinated polymers represents an advancement in material performance, offering substantial potential for the development of electronic materials.