The Effect of Nanofillers on the Viscoelastic Creep Behavior of Thermoplastics

The use of polymer nanocomposites (PNCs) in infrastructure applications requires a comprehensive understanding of the mechanism of nanoparticle reinforcement during viscoelastic creep. Some of the most relevant parameters that impact the mechanical reinforcement of nanoparticles to a thermoplastic matrix are the nanoparticle size and concentration, and the interaction between the nanoparticle surface and the polymer matrix. In this study, the long-term creep behavior of a model nanocomposite system is examined by applying time-temperature superposition to dynamic mechanical analysis (DMA) of PNC films at temperatures between T_g-60 °C and T_g+60 °C. The PNC system is composed of monodisperse 10-nm, 15-nm, and 28-nm silica nanoparticles dispersed in an amorphous polymer matrix of approximately 200,000 g/mol weight-average molecular weight. The interaction between nanoparticle surface and polymer matrix is adjusted by using bare silica featuring hydroxyl surface groups capable of hydrogen bonding versus nanoparticle surfaces treated with a phenyl-capping agent. The effect of these parameters on PNC morphology is quantified by small-angle X-ray scattering (SAXS) and by transmission electron microscopy (TEM), and correlated to the long-term viscoelastic creep behavior observed by DMA.