L‐Cysteine‐Encapsulated MXene Nanosheet Possessing Ultra‐Antioxidation in Aqueous Suspension for Electrophoretic Deposition Assisted Carbon‐Fiber‐Surface Modification

Abstract With recent progress in 2D materials, Ti 3 C 2 T x MXene featured high metallic electrical conductivity, high electromagnetic interference shielding effectiveness, and super in‐plane stiffness, exhibits unique advantages in many fields, but is rarely applied as a sizing agent in long‐time continuous processing of carbon fiber sizing because of its poor ambient stability in aqueous suspension. Herein, a new strategy to chemically encapsulate the reactive sites of MXene nanosheet with l ‐cysteine for restricting the attacking of water and/or oxygen in aqueous suspension is proposed. Based on the ultra‐antioxidation, polarity, and electrical properties of l ‐cysteine‐encapsulated Ti 3 C 2 T x MXene (LC‐MX) nanosheet, the LC‐MX, even if aging for weeks in aqueous suspension, can be deposited on the surface of high‐modulus carbon fiber (HMCF) uniformly via the electrophoretic deposition assisted sizing. Benefiting from the enhanced surface energy, wettability, and roughness of LC‐MX‐sized HMCF (HMCF‐LCMX) relative to that of unsized one (U‐HMCF), the interfacial property of HMCF‐LCMX/epoxy (EP) composites is also improved, for which the interlayer shear strength (ILSS) of the composite reached 88.5 MPa, 52.8% higher than that of U‐HMCF/EP composite (57.9 MPa). This work makes an essential step toward the application of ultra‐stable MXene nanosheet suspension in large‐scale continuous carbon fiber sizing.