Multifunctional multilayer coatings: Enhancing durability through self-healing mechanisms activated via Joule effect

Abstract

A multilayer coating with multifunctional capabilities has been developed, consisting of an inner self-heating layer via carbon nanotube (CNT) addition into an epoxy resin with two different surface pre-treatments (non-treated and grit blasted), and an outer self-healing layer based on an epoxy/polycaprolactone (PCL) blend and an epoxy/2-aminophenyl disulfide (2-AFD). The analysis of the glass transition temperature (Tg) in the outer layer showed no significant differences between PCL and AFD-based mixtures, with values around 135 °C. The results of the electrical conductivity tests demonstrated that the grit blasting surface pre-treatment on the inner layer had no influence on the electrical conductivity. Indeed, all systems successfully reached the temperature to activate the vitrimeric behavior of the outer layer via resistive heating at voltages within the range of 80 to 140 V. Moreover, a novel self-healing test was conducted and recorded in an environmental scanning electron microscope (ESEM) chamber to establish the self-healing time required to achieve a high crack recovery efficiency. Finally, the results of the self-healing tests under convective and Joule heating show comparable healing efficiencies, exceeding 82 % in all study conditions showing a good capability for an autonomous repair and increasing the accessibility in difficult conditions such as offshore wind energy