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A B S T R A C TIn this study, desized carbon fibers were coated with carbon nanotubes using two diverse coating techniques, i.e. dip coating and spray up process, while the factors affecting the coating techniques were investigated. The morphological study revealed better nanotube coating on carbon fibers from dip coating technique as compared to spray up process. Later, nanotubecoated fibers from dip coating were impregnated with epoxy to fabricate multiscale carbon fiber reinforced epoxy matrix composites. The nanotubes on fiber surface were expected to improve the interlaminar shear properties of the multiscale composites. According to short beam shear testing, 14% increase in interlaminar shear strength was observed in composite containing nanotubes as compared to reference composite. Microscopic observation under optical and electron microscopes confirmed the void-free impregnation of fibers with epoxy along with the presence of nanotubes on fibers and in matrix in the vicinity of fibers. Finally, the mechanisms involving the enhanced interlaminar properties were identified and discussed.

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Carbon fiber reinforced polymeric matrix composites are enormously used in aerospace and automotive industries due to their enhanced specific properties. However, the area of interlaminar shear properties still needs investigation so as to produce composites with improved through-the-thickness properties. To improve interlaminar shear properties of these composites, acid-functionalized multiwalled carbon nanotubes were deposited on de-sized carbon fibers through electrophoretic deposition. De-sizing of carbon fabric was performed through three different methods: furnace heating, acidic treatment and chloroform usage. As the acid-treatment provided better results than other two techniques, the acid-de-sized carbon fibers were coated with nanotubes and subsequently incorporated in epoxy matrix to prepare a novel class of multiscale composites using vacuum assisted resin transfer molding technique. Nearly 30% rise in the interlaminar shear strength of the composites was obtained which was credited to the coating of nanotubes on the surface of carbon fibers. The increased adhesion between carbon fibers and epoxy matrix due to mechanical interlocking of nanotubes was found to be the possible reason of improved interlaminar shear properties.

Two-dimensional glass fibers reinforced silica matrix composites (GFS) were fabricated by silica sol infiltration (SSI) method by varying the number of infiltration cycles. A uniform weight gain was observed after each infiltration up to 9 th infiltration suggesting the uniform loading of nano silica within GFS composites. The relationship between the infiltration cycle and the physical and flexural behavior of composites was measured by means of a density and 3-point flexural test along with supporting evidences via microstructural characterization. The results of mechanical testing indicated an increase in the flexural properties by up to 25%, after each infiltration cycle, due to increase in density. Finally, microstructural study revealed the presence of various toughening mechanisms during fracture, under flexural loading in the GFS composites.