Inhibitory effect of silane modification on hygrothermal degradation of carbon fiber/epoxy interfaces: Multi-scale investigation

This study investigated the hygrothermal degradation and stabilization mechanisms of silane-modified carbon fiber/epoxy interfaces through a multi-scale approach combining microscopic experiments and molecular dynamics (MD) simulations. A three-step “oxidation-reduction-grafting” method was successfully employed to construct a robust Si-O-C covalent bridging network on the fiber surface, overcoming its inherent chemical inertness. Experimental results revealed that silane modification improved the dry interfacial shear strength (IFSS) by 117% and imparted exceptional environmental resistance, with a strength reduction of only 0.25% under high-temperature and wet conditions, compared to 15.21% for the unmodified interface. MD simulations further revealed that the grafting density plays an important role in regulating interfacial performance and failure behavior. The hygrothermal resistance mechanism stems from a profound synergy between space-filling effects and electrostatic repulsion: the grafted chains effectively occupy interfacial free volume and sever moisture diffusion channels, while high-density negative charge regions create a Coulombic repulsion field that elevates the energy barrier for polar water molecules to approach the interface. However, excessive grafting leads to packing defects due to steric hindrance, undermining the shielding effect.