An Interface-Driven Stiffening Mechanism in Polymer Nanocomposites

Erkan Senses and Pinar Akcora *

Dynamic mechanical response in responsive and adaptive composites can be achieved either through the responsive polymer; with the chemical regulators affecting the bonding between fillers or through reversible covalent bonding. Tuning the interfaces between fillers and polymer matrix potentially plays a critical role in all these systems to enhance their adaptive responses. Here, we present that the bonding–debonding of chains on nanoparticles can be modulated under extensive periodic strains. Mechanical response of an attractive model polymer composite, poly(methyl methacrylate) filled with silica nanoparticles, is monitored in a series of deformation–resting experiments allowing us to tune the interfacial strength of polymer. Chains that are desorbed from the surface with the oscillatory shear entangle with the free chains during the rest time. We show that periodic deformation process results in unusual stiffening of composites. Mechanical response during the recovery reveals this behavior arising from the enhancement in the entanglement of chains at interfaces. The interfacial hardening can be used in designing polymer composites with stress-sensitive interfaces to achieve new repair mechanisms for biomedical applications, and also in energy absorbing reinforced systems.

Interesting paper on the stiffening of composites based on periodic input stress.