Multiphase multiscale particle-nanofiber interactions in composites

Composite nanofibers have been of growing interest in various areas of science and engineering. They are intriguing due to tailorable properties by composition and/or the processing methods. Composite nanofibers can be produced from polymer solutions and suspensions with non-polymeric phases for multi-functionality. Material/processing development and materials characterisation aspects of this class of materials have great potential for novelty as also sought in this dissertation. Among the various manufacturing methods, electrospinning is a versatile and established technique as also intensively used in this dissertation. Properties of the electrospun composite nanofibers can be modified by manipulation of the polymer chemistry and hybridization of multiple phases to polymer solutions. In this research, composites nanofibers were mostly used to interleave epoxy matrix carbon and aramid fiber reinforced composites. Aramid fiber woven fabric with phenolic binder layers was also utilized to host the nanofibrous interlayers. They were used as toughening agents of the interlaminar region of these composites. Characterization of electrospun nanofiber composites is a major challenge in materials science and engineering. The present dissertation focuses on the hybridization of several types of polymers and non-polymeric phases which are produced by electrospinning technique. Also, it proposes special characterization methods using scanning electron microscopy. Several nanofiber composites were obtained from polystyrene, copolymerized poly[styrene-co-(glycidyl methacrylate)], polyacrylonitrile, and copolymerized poly[acrylonitrile-co-(glycidyl methacrylate)]. Several multiphase composites were produced through the hybridization of polymers and particles including vi milled carbon fibers and zirconia polymorphs. Composite nanofibers were produced through single and dual electrospinning method, facilitating tailorable properties in the vicinity of particles. Several characterization methods were implemented, including thermogravimetric analysis, dynamic scanning calorimetry, x-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, optical microscopy, scanning electron microscopy, universal testing machine, and micro-indentation. Computer programming was utilized for image processing, statistical analysis, and data visualization through coding in MATLAB and Python. Overall, multiphase composite nanofibers were able to improve the mechanical performance of composites, standing out as an effective method in the future of the composite design and engineering. This study includes the following novelties in the material development and processing: 1) synthesis of a new polymer by copolymerization of acrylonitrile monomer and glycidyl methacrylate, poly[acrylonitrile-co-(glycidyl methacrylate)], 2) synthesis of new multiphase interlayer with milled carbon fiber, 3) introduction of interface tailoring through dual electrospinning. This study includes a new method of characterization based on the secondary electron signal of polymorphs