Spatial resolution comparison of AC-SECM with SECM and their characterization of self-healing performance of hexamethylene diisocyanate trimer microcapsule coatings

Abstract

Hexamethylene diisocyanate trimer (HDIt) microcapsules were synthesized by in situ polymerization and were characterized via field emission-scanning electron microscopy, fluorescence microscopy, and Fourier transform infrared spectroscopy. We added HDIt microcapsules into epoxy resin coatings as functional additives and then assessed the resulting self-healing performance of the epoxy resin coatings using a scratched crevice on a 5083 aluminum surface as a test scenario. The protective coating with the HDIt microcapsules had robust self-healing after the samples were immersed in a solution of 0.6 M NaCl for 48 h. Healing efficiencies of epoxy resin coatings as high as 45.3 ± 2.9%, characterized by a fracture test, were achieved for 16 wt% HDIt microcapsules. The self-healing ability was further shown by using scanning electrochemical microscopy (SECM) and alternating current scanning electrochemical microscopy (AC-SECM). We found that AC-SECM offered additional local electrochemical topographies of the self-healing surface at different AC frequencies. Comparing the two topographical tests obtained from both SECM and AC-SECM revealed that AC-SECM achieved better spatial resolution and was less influenced by the scanning step size and the cleanliness of the tip surface.