Thermally Activated Shear Stiffening in Polymer-Grafted Nanoparticle Composites for High-Temperature Adhesives

Thermally activated shear stiffening viscoelastic fluid can help to improve the performance of viscoelastic dampers and high-temperature adhesives. Polymer nanocomposites with heterogeneous interphases are applied to design such adaptive materials. In this work, shear stiffening in polymer-grafted nanoparticle composites is investigated. We report the linear rheological responses of grafted particle composites before and after large-amplitude oscillatory shear application. We found that interfacial mixing of short grafts with chemically different long matrix chains led to the enhancement of plateau moduli and terminal relaxations, unlike with the long grafts. Moreover, we showed that the elastic modulus of grafted chains was enhanced upon deformation through inter-diffusion and entanglements of interfacial layers with the short matrix chains in both grafted systems. These results suggest that dynamic coupling between chemically different polymers away from nanoparticle surfaces is a design strategy to achieve the thermally stiffening behavior in polymer nanocomposites.