Theory for the Elementary Time Scale of Stress Relaxation in Polymer Nanocomposites

We construct a microscopic theory for the elementary time scale of stress relaxation in dense polymer nanocomposites. The key dynamical event is proposed to involve the rearrangement of cohesive segment-nanoparticle (NP) tight bridging complexes via an activated small NP dilational motion, which allows the confined segments to relax. The corresponding activation energy is determined by the NP bridge coordination number and potential of mean force barrier. The activation energy varies nonlinearly with interfacial cohesion strength and NP concentration, and a universal master curve is predicted. The theory is in very good agreement with experiments. The underlying ideas are relevant to a variety of other hybrid macromolecular materials involving hard particles and soft macromolecules.

Automated summary

We present a microscopic theory for stress relaxation in dense polymer nanocomposites, which is based on the rearrangement of cohesive segment-nanoparticle (NP) bridging complexes. The key dynamical event involves the activated motion of small NPs, allowing the confined segments to relax. The activation energy depends on the NP bridge coordination and potential of mean force barrier, and it shows a nonlinear variation with interfacial cohesion strength and NP concentration. The theory is in excellent agreement with experimental results, and it has implications for other hybrid macromolecular materials.