Tannic Acid Surface Modification Enhances Carbon Fiber/Epoxy Interfacial Adhesion: Experiments and Multiscale MD–FEM Analysis

Abstract

Interfacial adhesion strongly affects the load-transfer efficiency and mechanical performance of carbon fiber/epoxy composites. In this study, an APTES-assisted tannic acid (TA) (TAP) interphase was constructed on carbon fibers through APTES pretreatment followed by TA deposition. Experimental characterization, molecular dynamics (MD) simulations, and finite element analysis were combined to investigate the interfacial strengthening mechanism. TAP modification increased the surface roughness, wettability, and interfacial activity of the fibers without reducing their single-filament tensile strength. The water and diiodomethane contact angles decreased to 45.2° and 42.5°, respectively, while the surface free energy increased from 30.0 to 59.8 mJ/m2. The interfacial shear strength increased from 49.2 to 82.4 MPa, while the interlaminar shear strength of the corresponding composites increased from 59.3 to 87.7 MPa, representing improvements of 67.5% and 47.9%, respectively. Improved hydrothermal stability was also achieved. MD simulations revealed enhanced interfacial interactions and stronger adsorption of epoxy molecules, while finite element analysis showed improved load transfer and delayed damage propagation. These results demonstrate the effectiveness of TAP modification for improving carbon fiber/epoxy interfacial adhesion.