Enhanced Strength and Modulus in Low Graphene‐Carbon Fiber Epoxy Composites Achieved by Optimizing the Electrodeposition Parameters and Solution Concentration

ABSTRACT Graphene deposition to the carbon fiber (CF) is an effective method to enhance the interfacial strength and overall mechanical properties of CF epoxy composites. However, graphene deposition morphologies on to the CF such as wrap/cover, transverse/vertical, and partial wrap/cover play an important role in enhancing tensile, flexural, and interlaminar shear strength (ILSS) properties due to variations in interphase thickness. Earlier studies primarily focused on wrap/cover morphologies, which improved ILSS and interfacial shear strength but did not show significant improvement in tensile or flexural properties. In this study, electrophoretic deposition (EPD) process parameters and solution concentration were optimized to achieve a lower weight percentage (wt.%) of carboxyl graphene (G‐COOH) deposition of transverse/vertical morphologies, specifically R‐0.1 (0.1 wt.% with lowest graphene concentration), 0.1, 0.2, and 0.3 wt.%. Contact angle measurements of these G‐COOH deposited CF fabrics exhibited hydrophobic behavior due to the increased surface roughness resulting from the transverse/vertical morphologies, despite the presence of hydrophilic Mg(OH) ₂ /MgO deposited on the CF during EPD. The significant enhancement of unnormalized and normalized tensile strength (48% and 78%), unnormalized and normalized flexural strength (27% and 54%) and normalized ILSS (11%) achieved for the lower wt.% (R‐0.1 wt.%) of G‐COOH deposition compared to previous studies. All mechanical properties were normalized to a 50% fiber volume fraction to keep its effect constant, as it is a major governing factor, and to isolate the effect of graphene deposition. The fabricated composites exhibited the increased interphase thickness w.r.t G‐COOH deposition wt.%, while only slight differences in void fraction were observed among the composites. Significant differences in the signature of fracture were observed among different composites owing to different levels of delamination and fiber‐pullout.