Exfoliation and defect control of graphene oxide for waterborne electromagnetic interference shielding coatings

Graphene oxide (GO) prepared by Hummers' method possesses many structural defects which decrease its conductivity and limit its application in electromagnetic interference (EMI) shielding. Highly exfoliated GO with less defects (LGO) was prepared by a combination of less oxidant dosage (only 1/3 of the original dosage) and ultrasound-assisted Hummers' method. The sulfonated reduced LGO (S-rLGO) was compounded with P(St-BA) latex to serve as EMI shielding composite via a blending-casting process. After thermal and chemical reduction, reduced LGO (rLGO) possesses much higher conductivity than reduced GO. With a S-rLGO loading of 25 wt%, a high EMI shielding effectiveness (SE) of 15.9 dB at only 0.25 mm is achieved. Meanwhile, the tensile strength of composite is improved by 1097% owing to the Tc-Tc interaction. LGO was demonstrated to possess both good structural integrity and exfoliation degree, proving its better potential than GO as precursor of graphene for broad application.