| Damage in polymeric coatings, adhesives, microelectronic components, and composites spans many length scales. For small scale damage, autonomic self-healing can repair multiple damage modes without manual intervention. In autonomic self-healing materials, a healing response is triggered by damage to the material. Size scale considerations, such as fiber interstitial spacing in advanced composites and thin bond lines in adhesives require development of smaller healing agent filled capsules.;An in situ encapsulation method demonstrating over an order of magnitude size reduction for the preparation of urea-formaldehyde (UF) capsules filled with a healing agent, dicyclopentadiene (DCPD) is developed. Capsules with diameters as small as 220 nm are achieved using sonication techniques and an ultrahydrophobe to stabilize the DCPD droplets. Mechanical properties of the epoxy/capsule composite are measured and compared to previous data for larger capsules (ca. 180 mum).;A variety of other microencapsulation techniques are developed to encapsulate reactive core materials and prepare new capsule architectures. Reactive epoxy resins and solvents are encapsulated in UF and also in double-shelled polyurethane-UF capsules to increase thermal stability. These resin-solvent core microcapsules are used to demonstrate the first full recovery of fracture toughness in a thermoset matrix. In addition, UF capsules prepared with diameters ca. 1.5 mum are used as Pickering stabilizers to develop a novel binary microcapsule architecture that allows the sequestration of two distinct liquids within the same microcapsule.;To investigate self-healing of an interface, a method is developed for sequestration of healing agent filled microcapsules and catalyst to the reinforcement-matrix interface. Microbond specimens, consisting of a single self-healing functionalized fiber embedded in a microdroplet of epoxy, are used to test virgin and healed fiber-matrix interfacial shear strength. When damage initiates at the fiber-matrix interface, the attached capsules rupture, and healing agent is released into the crack plane where it contacts the Grubbs' catalyst to initiate polymerization. Up to 44% recovery of virgin interfacial shear strength after full interfacial debonding is demonstrated. Additionally, no decrease in virgin interfacial shear strength for functionalized fibers is reported for the specific concentrations used to achieve recovery of interfacial shear strength. |
