Constructing Mechanochromic Fluorescent Interphase via Core–Shell Microcapsules: A Route for Interface Reinforcing and Damage Self‐Reporting of CFRP Composites

Abstract Perylenediimide‐chitosan/γ‐poly (glutamic acid) microcapsules sizing (PDI‐CS/γ‐PGA) core–shell microcapsule is designed and used to establish a novel interphase in carbon fiber/epoxy (CF/EP) composite, and the interfacial property, as well as the damage self‐reporting of the composite, is compared with desized carbon fiber (CF‐desized)/EP and commercial carbon fiber (CF‐COM)/EP composite. The ruptured PDI‐CS/γ‐PGA microcapsule exhibits strong “turn‐on” green fluorescence from the released PDI upon mechanical stimuli. The anchoring of PDI‐CS/γ‐PGA microcapsule on carbon fiber with PDI‐CS/γ‐PGA microcapsules sizing (CF@PDI‐CS/γ‐PGA) surface results in increased chemical activity and roughness, exhibiting a weak green fluorescence signal instead of non‐fluorescence on CF‐desized and CF‐COM surface. The transverse fiber bundle tensile (TFBT) strength of CF@PDI‐CS/γ‐PGA composite is 80.97% and 31.09% higher than those of CF‐desized/EP and CF‐COM/EP composite, which is attributed to the mechanical interlocking and chemical bonding interaction between carbon fiber and epoxy matrix by introducing PDI‐CS/γ‐PGA microcapsule with spherular structure and active groups. After microdroplet testing, the strong “turn‐on” green fluorescence signal of the released PDI from the microcapsules is detected in the interfacial debonding regions, realizing the microscopic damage self‐reporting of CF@PDI‐CS/γ‐PGA composite.