Wetting dynamics and surface energy components of single carbon fibers

Measuring contact angles made by liquids around individual carbon fibers (CFs) using the Wilhelmy technique is a conventional method to evaluate their surface properties. However, despite its apparent simplicity, inaccurate measurements of capillary forces and wetted lengths, due to the fineness of the CFs, as well as an improper selection of probe liquids can lead to incorrect contact angle and surface energy calculations, leading to an erroneous characterization of their surface properties.

In this study, dynamic wetting experiments of individual CFs were performed in ethylene glycol, diiodomethane, and formamide based on the Wilhelmy method. Capillary forces exerted on the CFs were recorded and analyzed in detail to calculate reliable dynamic contact angles at different contact-line velocities. The molecular-kinetic theory (MKT) and hydrodynamic approach (HD) were then used to model the experimental data and to obtain static contact angles.

The analysis shows that the experimental data are in good agreement with the linear MKT suggesting that the dominant channel of energy dissipation at the contact line is the contact-line friction. From the predicted static advancing contact angle values, the surface energy components of the CFs could be obtained thus providing a way to characterize their interfacial properties and predict their compatibility with polymer matrices. This study furthermore points out the importance of choosing the correct combination of test fluids to obtain reliable surface energy results.