Unraveling the Mechanism of Nanoscale Mechanical Reinforcement in Glassy Polymer Nanocomposites
by Shiwang Cheng, Vera Bocharova, Alex Belianinov, Xhaomin Xiong, Alexander Kisliuk, Suhas Somnath, Adam P. Holt, Olga S. Ovchinnikova, Stephen Jesse, Halie Martin, Thusitha Etampawala, Mark Dadmum, Alexei P. Sokolov
The mechanical reinforcement of polymer nanocomposites (PNCs) above the glass transition temperature, Tg, has been extensively studied. However, not much is known about the origin of this eff ect below Tg . In this Letter, we unravel the mechanism of PNC reinforcement within the glassy state by directly probing nanoscale mechanical properties with atomic force microscopy and macroscopic properties with Brillouin light scattering. Our results unambiguously show that the “glassy” Young’ s modulus in the interfacial polymer layer of PNCs is two-times higher than in the bulk polymer, which results in signifi cant reinforcement below Tg. We ascribe this phenomenon to a high stretching of the chains within the interfacial layer. Since the interfacial chain packing is essentially temperature independent, these findings provide a new insight into the mechanical reinforcement of PNCs also above Tg.