Damage sensing and self-healing materials through microencapsulation process

Smart materials are a class of materials able to respond to stimuli and environmental changes and to activate their functions according to these changes. The design, fabrication, and construction of smart structures is one of the ultimate challenges for engineering researchers today. With the aim to extend materials lifetime two types of smart materials are knowing a growing interest especially in the coating field: damage sensing and self-healing materials. The first ones allows the damage identification whilst the second ones possess the intrinsic capability to heal small cracks. A method for the production of materials with those advanced properties includes the microencapsulation, which is the process of enclosing a liquid core within a polymeric shell. The present work reports the fabrication of novel microcapsules characterized by a UV-screening shell and examples of composite coatings containing such microcapsules. After a mechanical damage is applied, the microcapsules rupture leads to the core diffusion into the matrix. The smart material functionality is then triggered by the UV light. In the damage sensing application a photochromic or fluorescent dye was encapsulated so that the corresponding composite could act as a damage sensor, showing a fluorescent signal when a scratch was applied on its surface to simulate a real damage and after subsequent exposure to UV light. The self-healing material has a similar action mechanism but differs in the encapsulated core. Experimentally, a UV-absorbing polyurea shell was obtained by reacting a polyisocyanate with an amine via a interfacial polymerization process. The influence of two types of amine on the UV-screening ability of the shell was investigated. Differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), scanning electronic microscopy (SEM), rheological analyses, optical microscopy and IR analyses demonstrated the successful encapsulation of various core materials. For the self-healing coatings fabrication, different photocurable resins were chosen as core material in the synthesis of microcapsules.