Effect of polymer-nanoparticle interaction strength on viscoelastic creep attenuation in polymer nanocomposites

Successful use of polymer nanocomposites (PNCs) in infrastructure applications requires a thorough understanding of the mechanisms affecting viscoelastic creep behavior in PNCs, including nanoparticle size, loading, and polymer-nanoparticle interaction strength. In this study, we examine the long-term creep behavior of a model nanocomposite system consisting of 13 and 52 nm diameter silica nanoparticles (NPs) dispersed in a matrix of 200 kg/mol poly(2-vinylpyridine) (P2VP). The polymer-nanoparticle interaction strength is controlled by functionalizing the nanoparticle surface with varying densities of methoxy(dimethyl)octylsilane. to achieve a range of nanoparticle surface chemistries, resulting in a variety of systems from strongly attractive bare-silica/P2VP composites to weakly attractive densely functionalized octyl-silica/P2VP composites. The long-term viscoelastic creep behavior of the composites is measured using dynamic mechanical analysis (DMA). The results are correlated to observations of the nanoparticle dispersion within the PNC, as quantified using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), as well as NP surface energy measurements via inverse gas chromatography (IGC).