Wettability of carbon fibres at micro- and mesoscales

Physical adhesion between Carbon Fibres (CFs) and polymer matrices as well as the formation of voids at the interface between these two materials are mostly controlled by the wetting properties of the fibres. Due to the hierarchical structure of CF reinforcements, it is essential to study their wetting behavior at different scales: from the single fibre (microscale) to the fabric (macroscale) via the tow scale (mesoscale). Probing the wettability of CF tows is, however, highly challenging, because it couples the effects of surface chemistry and geometry of the fibre assembly characterized by spontaneous capillary wicking and elasto-capillarity induced aggregation. Therefore, we first developed a new methodology combining a tensiometric method and a synchronized in-situ optical observation technique to better characterize the wettability of CF tows. We then used it to evaluate the difference in wettability between tows composed of unsized and sized (T300) CFs. By comparing their wettability at the micro- and mesoscale, we could quantify how the modification of the surface chemistry at the microscale is transferred to the mesoscale.