Effect of plasma modification on the anisotropic surface structure of PAN-based graphitic carbon fiber

Plasma treatment is widely used to modify carbon fiber (CF) surfaces to improve their adhesion to the matrix. Commercial polyacrylonitrile (PAN)-based CFs (T700S and T800H) were plasma-treated after heat treatment at 2700 °C. The different types of domain structures observed on the surface of CFs were closely related to their microstructure as well as physical properties. X-ray photoelectron spectroscopy analysis of the plasma-treated CF surface showed a significant increase in oxygen concentration. AFM revealed that both heat and plasma treatments induced morphological changes at the submicron and nanoscales by tracing the growth and breaking of domains. Notably, enhanced surface roughness contributed to better interfacial adhesion in composites by providing a larger contact area between the CFs and the matrix, resulting in stronger mechanical interlocking at the interfaces. Plasma-treated samples for 10 min exhibited 3.0 to 5.6 times higher IFSS values compared to those of the heat-treated CFs. Additionally, FE simulations demonstrated that surface roughness can create significant mechanical interlocking at the interface, leading to significant variations in interface behavior between the transverse and longitudinal directions. This allows for an observation of the changes in the surface chemistry after modifications are applied to industrially available heat-treated CF.