Abstract
A methodology to enrich epoxy coatings of an effective self-healing feature on wet surfaces was developed as a further step on for practical corrosion protection issues. To this aim, a polyetheramine was chemically engineered by grafting catechol units and then successfully encapsulated in microcapsules (MCs) to be finally embedded into an epoxy resin deposited on steel panels. Fourier transform infrared spectroscopy (FTIR), thin-layer chromatography, and 1D and 2D nuclear magnetic resonance spectroscopy confirmed the successful polyetheramine modification by dopamine units. Different dosages of catechol-modified polyetheramine were encapsulated within poly(styrene-co-acrylonitrile) shell via electrospray method to study the influence of dopamine grafting on the healing performance. Scanning electron microscopy (SEM) analysis revealed the formation of the spherical MCs, while FTIR and TGA analyses confirmed the successful encapsulation. The highly responsive self-healing coatings were then prepared by embedding amine- and isocyanate-containing MCs (1:1 weight ratio; 3 wt% overall) as a dual-capsule system exploiting the polyurea formation as a fast healing reaction. In operando electrochemical impedance spectroscopy (EIS) tests were employed to study the underwater self-healing performance. According to the EIS results, monotonically increasing variation with time of the charge transfer resistance was correlated with a fast and effective underwater self-healing performance for the sample using 40 wt% of a catechol-modified healing agent. Such results, combined with others including SEM investigation on the underwater healed samples, point to an improved adhesion of the growing dopamine-bearing polymer to both underlying metal and epoxy edges of the scratch.Graphic abstract
Highlights
Nowadays, several self-healing techniques have been developed as promising approaches for increasing the service life of the organic coatings via controlling the crack propagation in their matrix [1,2,3,4]
According to the Fourier transform infrared spectroscopy (FTIR) results, the intermediate HDGE-grafted dopamine was successfully produced as the first stage toward the synthesis of the dopamine-modified prepolymer 1 (Fig. 1)
The present work has presented a proof-of-concept methodology to enrich epoxy coatings of an effective underwater self-healing feature through the chemical engineering of the healing agent with catechol units acting as anchoring sites
Summary
Several self-healing techniques have been developed as promising approaches for increasing the service life of the organic coatings via controlling the crack propagation in their matrix [1,2,3,4]. Considering the direct relationship between the steel corrosion phenomena and the presence of moisture and water in the environment, the ability for fast and efficient underwater self-healing is indispensable for effective self-healing anticorrosion coatings [8,9,10,11]. Cho et al studied the underwater healing performance through the incorporation of a poly(dimethylsiloxane)-based healing system in a vinyl ester matrix that revealed stable in the presence of moisture and water. They used methylacryloxypropyl triethoxysilane as the adhesion promoter, leading to enhance in the underwater self-healing performance. Lower stiffness and fracture toughness of PDMS with respect to the matrix material showed to be two important limitations in reaching a suitable overall efficiency [9]
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