The influence of shear rate and adsorbed polymer chain flexibility on thermally stiffening nanocomposites

The novelty of the nanocomposite used in the current work is that it thermally stiffens with increasing temperature. It consists of a low glass transition temperature (T_g) polymer matrix incorporating silica nanoparticles that contain an adsorbed high-T_g polymer. Although the unique thermal-stiffening property has great application potential, the weak interactions between the adsorbed polymer and nanoparticles make it vulnerable to severe shear stresses that are prevalent in standard processing operations. In the current study, a laboratory mixing extruder was used to process nanocomposites that were initially solution blended, as a function of shear rate and adsorbed polymer chemistry. The extrudates were characterized via multiple methods such as electron microscopy, small angle X-ray scattering, and rheometry. Results indicated that the extrusion process altered the dispersion and distribution of nanoparticles, thereby, leading to changes in the mechanical properties depending on the adsorbed polymer chain flexibility – systems with flexible adsorbed chains recovered most of their mechanical performance. The effect of adsorbed chain flexibility provides an insight into designing thermally stiffening nanocomposites with better processability.