Effect of silane-bridging on the dispersion of polyetheramine-functionalized graphene oxide in waterborne epoxy composites

Corrosion resistance of waterborne epoxy (WEP) coatings can be enhanced by the addition of graphene sheets as the physical barriers. The dispersion of graphene sheets in the WEP matrix is one of the key issues. Here, silane coupling agent was introduced in polyetheramine functionalization of graphene oxide as the molecular bridge via a two-step modification. Firstly, hydrolyzed silane was reacted with the hydroxyl groups of graphene oxide. Then, polyetheramine was grafted on the silanized graphene oxide, producing D-SGO. A long molecular tail with amino end groups was introduced on graphene surfaces, enhancing the steric hindrance, the compatibility with epoxy curing agent, as well as the interfacial bonding with WEP matrix. The interlayer spacing between polyetheramine-functionalized graphene oxide layers was increased from 1.13 nm to 1.77 nm by the silane-bridging. The molecular structure of D-SGO was analyzed by chemical characterization and molecular dynamics simulations. The two-step modification not only increased the length of the grafted molecules, but changed the reaction sites from the carboxyl groups at the graphene edges/defects to the hydroxyl groups on the basal plane. The insert of silane-bridging improved the dispersion of D-SGO. According to impedance measurements, the modulus of D-SGO(0.2%)/VVEP was kept at 5 x 10(9) Omega cm(2) for 4 months. The superior anticorrosion performance benefited from the barrier properties of well-dispersed D-SGO and the enhanced interfacial bonding between D-SGO and the WEP matrix.