Enhancing Self-Healing Properties of Polymeric Nanocomposites through Surface Modification of Van der Waals 2D Materials: Exploring Beyond Graphene.

Abstract

Engineering materials are designed to meet the demand for improved mechanical properties, including necessary fatigue resistance, fracture toughness and ability to withstand the mechanical damage inflicted during constant loading and unloading of stresses under the application. Nevertheless, microcracks and other structural defects can still be formed under the influence of external factors involved in their operation. In this work, surface-modified Van der Waals 2D materials, such as transition metal dichalcogenides (TMDs), hexagonal boron nitride (hBN) and MXene have been incorporated as nanofillers in polymer matrices to enhance their self-healing capabilities. The surface modification of these 2D materials with suitable functional chain ends is achieved and the resulting nanosheets possess the ability to chemically bond with the polymer matrix and actively participate in the healing chemistry. The thesis begins with a comprehensive review of the state-of-the-art in 2D materials-based self- healing polymeric composites and their applications, highlighting the fabrication techniques, methods for characterization and mechanics of bonding. The subsequent chapters focus on synthesizing and characterizing surface-functionalized hBN and WS2 along with their possible integration into different model polymer matrices. The influence of different parameters, such as filler loading, surface functionalization, and polymer matrix composition, on the resulting nanocomposites' self-healing efficiency and mechanical properties has been investigated. The developed polymer nanocomposites' healing mechanisms and the nanosheets' functionalization mechanisms are elucidated through detailed microscopic and spectroscopic analysis. The role of interfacial interactions between the 2D nanofillers and polymer matrices in facilitating an efficient healing process was investigated, and novel strategies for optimizing the healing performance were proposed such as alignment of nanosheets. Mechanical testing of the nanocomposites shows significant improvement in the healing and mechanical properties of surface-modified 2D materials due to enhanced adhesion with the polymer matrix. Further, the detrimental effects of nanosheet agglomeration, the lateral size of the nanofillers, and functional group loading on the nanosheets are also studied. The incorporation of 2D nanosheets into the polymers also gives valuable insights into the molecular interactions occurring during the functionalization of nanosheets and the healing of nanocomposites. The results presented in this thesis contribute to the development of novel materials with enhanced mechanical properties and extended lifespan, opening up new avenues for applications in diverse fields such as aerospace, automotive, and biomedical engineering.