Electron microscopy study of surface-treated carbon fiber for interface modification in composites

Relatively poor adhesion of carbon fibers with matrix leads to various serious concerns in high performance composites. Interface debonding during loading is the most vulnerable among them particularly when polymer matrix is used. This paper presents the results of electron microscopy investigation of four different techniques that are beneficial for improving interfacial bonding. These techniques were based on modifying the fiber surface by way of both; coating a film on the fiber and ablating a layer from it. The former employed growth of nanostructures of carbon and zinc oxide by thermal catalytic chemical vapor deposition and magnetron sputtering respectively and depositing a layer of pyrolytic carbon by CVD while the latter involved ablation of an outer layer of fiber using femtosecond laser treatment. Both the approaches relied on introducing mechanical anchoring on the fiber surface by micro roughening anticipating an improved fiber- matrix interfacial bonding. Carbon fiber surface prior and post treatment was investigated microscopically using FESEM and TEM. CNTs growth formed network like structure around the fiber, while PyC coating showed continuous layer around the fiber. HRTEM images of ZnO nanostructures; both nanowires and nanowalls possessed crystalline structure revealed by the presence of Moire fringes formed due to overlapping of two crystals with different orientation. Laser treated fiber surface showed formation of LIPSS with average periodicity of 147 +/- 10 nm.