Nanocomposites of Epoxy with Fe3O4 Featuring Dynamic Disulfide Bonds: Fracture Toughness, Reprocessing, and Functional Properties

Nanocomposites of epoxy with Fe₃O₄ featuring dynamic disulfide bonds were fabricated. To facilitate the dispersion of Fe₃O₄ nanoparticles, we synthesized poly(ε-caprolactone)-grafted Fe₃O₄ nanoparticles, which were then incorporated into epoxy to generate robust interfacial interactions between epoxy and the inorganic nanoparticles. Through this approach, a fine dispersion of the inorganic nanoparticles in the epoxy matrix was successfully obtained. The incorporation of Fe₃O₄ nanoparticles with fine dispersion resulted in the epoxy being effectively toughened; the critical stress field intensity factor (K_IC) was enhanced twice as the control epoxy. Thanks to the integration of the dynamic covalent bonds (i.e., disulfide bonds), the nanocomposites displayed excellent reprocessable or recyclable properties. Depending on the contents of poly(ε-caprolactone)-grafted Fe₃O₄ nanoparticles, the nanocomposites can be modulated to have shape recovery with the desired shape transition temperatures. Benefiting from the dynamicity of disulfide bonds, the shape memory behavior featured reconfigurability. Inheriting from the nature of Fe₃O₄ nanoparticles, the nanocomposites likewise displayed superparamagnetic and photothermal properties. By taking advantage of the photothermal behavior, shape memory can be triggered through infrared laser irradiation and in a noncontact manner.