Dispersion and parallel assembly of sulfonated graphene in waterborne epoxy anticorrosion coatings

Graphene derivatives can function as a barrier reinforcement in waterborne epoxy (WEP) coatings. The main challenge lies in the demulsification of epoxy emulsions caused by the addition of graphene derivatives and the dispersion of graphene sheets with a relatively high filler content. Herein, sulfonic acid groups were grafted on the edges of graphene sheets. The sulfonated graphene (SG) can be stably dispersed in water and waterborne epoxy emulsions, while graphene oxide (GO) caused demulsification of epoxy emulsions. Assembly of SG sheets at oil/water interfaces in WEP emulsions was proposed, which co-stabilized the WEP emulsions. SG reinforced WEP coatings were fabricated on carbon steel plates for corrosion protection. When the SG content was 0.2 wt%, SG sheets were nanoscopically well dispersed in WEP coatings. With the increase of the SG content, the SG sheets tended to assemble parallelly in short ranges, leaving a distance of 20-30 nm between the neighboring sheets. The corrosion protection properties of the coatings were significantly improved by the dispersed SG sheets, as well as the parallelly assembled SG sheets. The most remarkable improvement was achieved by adding 1.0 wt% SG into the WEP coatings, where the impedance modulus at 0.1 Hz was 193 times higher than that of the neat WEP coatings after 150 days of immersion in electrolytes. The outstanding corrosion protection properties were attributed to the stable WEP emulsions, the physical barrier properties of SG, the high SG content, and the sufficient distance between the parallelly assembled SG.