In this study, the surface of silica was modified by direct fluorination treatment at different temperatures. The effect of fluorinated silica (F/Si) on the interfacial mechanical properties and thermal stability of acrylonitrile-butadiene rubber (NBR) composites was investigated. The surface properties of the silica were determined by infrared spectroscopy, X-ray photoelectron spectroscopy, and solid NMR measurements. The resultant interfacial mechanical properties and thermal stability of the composites were characterized by tearing energy (G(IIIC)) and decomposition activation energy, respectively. It was found that the number of fluorine groups introduced onto the silica surfaces increased with increasing temperature of fluorination, resulting in more uniform dispersion of silica in the NBR matrix. As a result, the G(IIIC) of the F/Si-NBR composites significantly increased compared to the non-treated silica/NBR composite and the highest value was found to be 65% higher. These results could be attributed to the strong intermolecular interactions between F/Si and NBR matrix in composites. (C) Koninklijke Brill NV, Leiden, 2012