Novel routes to liquid-based self-healing polymer systems

Inspired by the current state-of-the-art and the progressing advancements in the field of self-healing materials, this thesis addresses several novel routes to advance the concept of liquid-based self-healing polymer systems. This thesis presents the concept and characterisation of a one-component solvent-based healing mechanism for thermoplastic materials and in addition to the healing strategy, a new capsular architecture is proposed for the purpose of simultaneous release of two reactants at the same location. Other liquid container designs are investigated to enhance the liquid release upon fracture (also in the case of multiple healing events) and come with less scarification of the intrinsic material properties. Chapter 2 describes the theoretical and experimental evaluation of all the material system parameters that are significant in the performance of a one component solvent-induced selfhealing mechanism for thermoplastic materials. Parameters that are investigated include solvent sorption rates, solvent induced depression of Tg and polymer diffusion coefficients. In Chapter 3 autonomous solvent-induced self-healing mechanism for PMMA are presented and investigated. The self-healing of the mechanical properties is experimental validated for different solvents and capsule volume concentration as a function of the healing time. In Chapter 4 the capsule-composite thermoplastic self-healing material is characterised qualitatively and quantitatively by X-ray tomography using SEM-based and Synchrotron X-ray facilities. The techniques allow detailed investigation into the release volume and kinetics ofhealing-agent at the damaged site. Chapter 5 presents a novel microcapsular architecture, designed for the encapsulation of two individual liquids within a single microscopic structure. These binary microcapsules have a central liquid core and are peripherally decorated with the second liquid component, which is achieved by the synthesis and application of liquid-filled Pickering particles. Chapter 6 presents a numerical study into the influence of the microcapsule geometrical shape on the performance of a self-healing material. Classical spherical shapes are compared to cylindrical ones with varying degree of anisotropy and spatial orientation. In Chapter 7 production routes are evaluated to obtain anisotropic rod-like microcapsules. The investigated routes involve droplet deformation and encapsulation in shear and elongational flow, by usage of a modified ink-jet printing technique and by creation of stable anisotropic droplets in suspension using Pickering particles. In Chapter 8 the concept for a compartmented liquid-filled fibre is given, providing an alternative to the continuous capillaries and discrete spherical microcapsules currently applied in the field of self-healing. Control over the morphology allows production of fibres with different mechanical properties that are in the order of standard composite matrix materials and have slightly lower failure strains.