Creation of a nanovascular network for use in self healing applications

Self healing methodologies are being developed to extend the lifetime of materials. Extrinsic self healing systems are based on the introduction of microcapsules, hollow fibers or a microvascular network. The latter one allows flow of the healing agents and multiple healing cycles. Although a lot of progress has been made, the effect of introducing such healing feature on the mechanical properties of the neat material is mainly overlooked. A compromise between the channel size to allow good flow of the healing agents in them and a limited deterioration of the intrinsic mechanical properties of the matrix when introducing channels has to be found. In this work, a nanovascular network for self healing applications was developed. To do so two different approaches are used, a sacrificial fibre methodology to create nanochannels and core shell nanofibers. For both, electrospinning of a natural polysaccharide (pullulan) is used to produce nanofibers which are subsequently embedded in an epoxy matrix. A detailed parameter analysis allowed producing tailored pullulan nanofibers. The healing agents are epoxy and amine monomers. These will react whenever there is a crack produced in the material and the nanovascular network is broken. Therefore, the reaction and diffusion of several epoxy amine healing systems is investigated for the selection of the most appropriate system. Core shell nanofibers containing the liquid healing agent as core were produced by coaxial electrospinning. The effect of introducing the nanochannels or the core shell nanofibers on the mechanical properties of the epoxy matrix is studied. At the same volume fraction, finer fibres have a smaller impact on the mechanical properties. Finally, several methodologies to test the self healing capability are developed.