Physical mechanism for the mechanical reinforcement in nanotube-polymer composite materials

The significant increase in the Young’s modulus of nanotube-polymer composites is often correlated with the formation of a crystalline layer of polymers surrounding the nanotubes. Although the improved stress transfer between the stiffer nanotube and the softer polymer matrix has been attributed to the presence of this wellordered polymeric layer, the actual mechanism for this stress transfer is still unclear. To clarify this matter, we model the polymer-nanotube composite by harmonic chains interacting with a rigid periodic potential, an extension of the so-called Frenkel-Kontorova model. We identify the origin of the reinforcement with the occurrence of a templating transition, in which polymers are constrained by the periodic potential of the underlying nanotube. The model is potentially capable of predicting the ideal combination of polymers and nanotube diameters to maximally enhance the mechanical properties of composite structures.