Identification of interfacial and interphasal failure in composites of plasma polymer coated fibres

It has been demonstrated in previous work by this group that the mechanical properties of a glass fibre reinforced polymer composite can be improved by the deposition of a plasma polymer coating onto the fibres prior to their incorporation into the matrix. It was further demonstrated that the mechanical properties of the resulting composite could be tailored by adjusting the composition of the coating. More complete fractography of these composites has now been performed. Time of flight secondary ion mass spectrometry (ToF-SIMS) was used to identify the chemical species present on both the surface of the fibres and the composite fracture surfaces and so deduce their role in achieving adhesion between the fibre and matrix. By imaging the fracture surfaces with matrix, interphase and fibre specific secondary ions the locus of failure could be identified. It was found that changing the composition of the plasma polymer coating applied to the fibre moved the locus of failure from within the interphase to the interface. This demonstrates how the chemistry of the interphase can produce the desired fracture mechanics to optimise composite mechanical properties.