Fibres with ultra-high tensile strength have attracted unprecedented attention due to the rapidly increasing demand for strong fibre reinforced composites in various fields. However, despite a theoretical strength as high as around 46 GPa, current commercial alumina fibres only reach strength value of around 3.3 GPa because of the defects between the grains. Electrospinning provides a method to produce ceramic nanofibres with diameters reduced to nano-scale with effectively enhanced strength. Different calcination procedures were applied to study the morphology and crystal structure growth of alumina. Tested with a custom-built AFM-SEM system, the tensile strength of single crystal α-alumina nanofibres were found to have little dependence on diameter variations, with an average value of 11.4±1.1 GPa. While the strength of polycrystalline γ-alumina nanofibres were controlled by defects, showing a diameter dependent mechanism. Apart from the intrinsic properties of the fibre and matrix, the interface between them also plays an important role in determining composite mechanical properties. Collected by a rotating drum during electrospinning, aligned fibres were used to reinforce polycarbonate matrix for fabricating composite. The composite mechanical properties were successfully improved after surface modification with silane coupling agent. With a fibre volume fraction of around 7.5%, the composite strength doubled and the Young's modulus increased by a factor of 4 when compared with the pure polycarbonate. Apart from surface modification, the fibre/matrix interface can also be affected by transcrystallinity. Transcrystalline layers were formed in the alumina reinforced polycarbonate composites after annealing. Significant enhancement of the Young's modulus of the crystallized polycarbonate by a factor of 3 compared to the amorphous phase was measured directly using AFM based nanoindentation. Optimization of the Young's modulus is suggested as a balance between extending the annealing time to grow the transcrystalline layer and reducing the processing time to suppress void development in the PC matrix.

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In recent years, increased use of electronic devices and wireless operations resulted in unavoidable electromagnetic (EM) pollution which has a significant impact on civil and military sectors. Considering the foremost requirement, huge efforts were invested in the development of electromagnetic interference (EMI) shielding materials. In this context, metals are usually preferred but design complexities like high density and susceptibility towards corrosion are limiting factors; additionally, the reflection of microwaves from the surface fails to serve as EM absorbers. The concern here is to minimize the reflection of the high frequency electromagnetic wave from the surface and to enhance the microwave absorption in GHz frequencies. In this thesis, we have made an attempt to design EMI shielding materials with exceptional absorption ability derived from Polycarbonate (PC)/ Poly styrene-co-acrylonitrile (SAN) based polymer blends. Herein, unique co-continuous micro-phase separated blend structures with selective localization of microwave active nanoparticles in one of the phases were realized to be most effective for microwave attenuation over just dispersing it in one polymer matrix (i.e. PC and SAN composites). The synergistic attenuation of electric and magnetic field associated with EM radiation was achieved through incorporation of various magnetic nanoparticles, however, dispersion of magnetic nanoparticles was a challenging task. Therefore, in order to localize magnetic nanoparticles in PC phase of the blends and to enhance the dispersion state, various modification strategies have been designed. In summary, we have developed a library of engineered nanoparticles to achieve synergistic attenuation of EM radiation mostly through absorption. For instance, the PC/SAN blends containing MWNTs and rGO-Fe3O4 nanoparticles manifested in exceptional EMI shielding, well above required shielding effectiveness value for most of the commercial applications, essentially through absorption. Taken together, the finding suggests that immiscible blends containing MWNTs and the decoration of magnetic nanoparticles (rGO-Fe3O4) on the surface of reduced graphene oxide sheets can be utilized to engineer high-performance EMI shielding materials with exceptional absorption ability.