On the Rheological Properties of Polymer Nanocomposites

It is well known, that the properties of polymers can be improved by the incorporation of nano-additives in the polymeric matrix, forming nanocomposite materials that possess optimized physicochemical properties. In this work, we investigate the rheological response of different series of poly(ethylene oxide) / silica, PEO/SiO₂, nanocomposites by oscillatory shear rheology in the linear viscoelastic regime. SiO₂ nanoparticles of two different radii (7nm and 67nm) were dispersed in PEO of different molecular weights covering the regime from unentangled to highly-entangled systems; their fine dispersion was verified with Transmission Electron Microscopy (TEM), while their structure and morphology were investigated with X-Ray Diffraction (XRD) and Small Angle X-ray Scattering (SAXS). The effects of the size and concentration of the nanoparticles on the dynamic response of the nanocomposites were studied as well as the effect of the degree of entanglements when the PEO molecular weight was varied. The puzzling finding of the work was the decrease of the viscosity that was observed with the addition of nanoparticles at low concentrations; this works aims at explaining this behavior.