Study on the construction of polyethyleneimine/nano-silica multilayer film on the carbon fiber surfaces to improve the interfacial properties of carbon fiber/epoxy composites

To enhance the interfacial properties of carbon fiber (CF) reinforced epoxy composites without damaging the CF strength. The polydopamine (PDA) was used as the precursor layer, and polyethyleneimine (PEI) and nano-silica (nano-SiO2) were deposited on the surface of CF by layer-by-layer electrostatic self-assembly. The layered strengthening materials (CF-Ln) were prepared and the microstructure of the CF was systematically characterized. The results showed that when the number of self-assembled layers is 5 (CF-L5), nano-SiO2 covers the surface of CF uniformly, and the tensile strength of CF-L5 monofilament reaches the maximum value, which is 12.1% higher than that of untreated CF (U-CF). Meanwhile, the interface properties between CF-L5 and epoxy matrix have been significantly improved. The interfacial shear strength (IFSS) between CF-L5 and epoxy matrix is 99.4% higher than that of U-CF. The improvement of the interfacial properties between CF-L5 and epoxy matrix is due to the introduction of alarge number of active groups (-NH2, -OH) in the PEI/SiO2 multilayer film deposited on the surface of CF, which improves the wettability between the CF and epoxy matrix. Also, the nano-SiO2 increases the roughness of the CF surface and improves the mechanical engagement between the CF and epoxy resin.