This work assessed the relative effects of processing conditions and interfacial interactions on the structure and properties of PBS/fumed silica nanocomposites. Rheology and scattering were used to investigate the dispersion state of silica particles with different surface treatments in nanocomposites produced by ultra-high speed twin-screw extrusion. Structural parameters of the silica, such as fractal dimension and Fisher exponent, were estimated by low-frequency rheology responses and lower q scattering data. This study demonstrates that both decreased bulk polymer properties and improved filler suspension caused by high shear compounding determine the final properties of these PBS based nanocomposites. While the molecular weight of bulk polymer matrix was significantly reduced, the extreme shear increased the probability of forming percolated clusters, leading to remarkable reinforcement (up to 4000%) as evidenced by the low-frequency rheological response. Further, the improvement in dispersion was enhanced when the filler was functionalized with a compatibilizing surface treatment. (C) 2016 Wiley Periodicals, Inc.