Influence of oligomeric silsesquioxane coatings treatment on the interfacial property of CF/PAA composites

Carbon fibers (CF) were modified with different oligomeric silsesquioxane (SSO) coatings to improve the interfacial property of carbon fibers/polyarylacetylene (CF/PAA). The interlaminar shear strength (ILSS) of CF/PAA was tested to make out the effect of treatment. Atomic force microscopy (AFM) in the force modulation mode was adopted to study the cross-section surface of unidirectional CF/PAA composites and the relative stiffness of various phases, including CF, interphase and resin. Probability histogram and line distributing of CF/PAA cross-section surface relative stiffness, obtained from the statistical analysis of the relative stiffness image, were used to compare and study the interface characterizations of composites. The results show that the ILSS increases effectively and the effects on interfacial characterizations are different after the CF surface was modified with different SSO coatings owing to the different structures. Cage oligomeric silsesquioxane including large organic groups (Methacryl isobutyl-POSS) has the better treatment result. AFM observations lead to the conclusion that an interfacial transition layer with different morphology and stiffness appears in CF/PAA composites after being treated by the SSO coatings of different structures. It can be inferred that the appearance of the transition layer may contribute to the improvement on fibre/matrix adhesion.