New Self-Healing Coatings

Most self-healing materials to date show limited healability and high material/fabrication process costs. In our group, we have developed thermally triggered self-healing coating materials in which crack-closing occurs through a shape memory effect of a thermoset matrix and crack re-bonding occurs by diffusion of an interpenetrating thermoplastic component. In order to apply the coatings on metal substrates, two methods were used. In the first method, poly(e-caprolactone) (PCL) was electrospun onto the substrate, yielding a fiber web, and then an epoxy copolymer formulation (DGEBA/NGDE/Jeffamine D-230) was spin-coated onto the fiber web. Following epoxy cure, the interpenetrating composite coating exhibits the described self-healing characteristics. Our second method utilized polymerization-induced phase separation (PIPS) of epoxy and PCL, yielding a distinct morphology also amenable to self-healing. Phase separation kinetics and blend morphology was investigated using optical microscopy, turbidity measurement, and differential scanning calorimetry. For both approaches, structural self-healing (crack closure) was observed using microscopy, while functional recovery (corrosion resistance restoration) was investigated using linear sweep voltammetry on samples exposed to NaCl/ solution. Both approaches led to excellent structural and functional self-healing. From potentiostat results, corrosion current density and consequently, corrosion rate was calculated. Results indicate enhanced corrosion density for healed samples. Moreover, self-healing during immersion in water was proved to be effective, indicating applicability to naval and biomedical applications.

Acknowledgment: This project is sponsored by DOE through collaboration with NEI Corporation.