Tuning the structure and mechanical property of polymer nanocomposites by employing anisotropic nanoparticles as netpoints

Bimodal Polymer End-Linked Nanoparticle Network Design Strategy to Manipulate the Structure-Mechanics Relation

A kind of bimodal polymer end-linked network employing nanoparticles (NPs) as net points has been designed and constructed through coarse-grained molecular dynamics simulation. We systematically explore the effects of the molecular weight (length of the long polymer chains), chain flexibility, and temperature on the accurate distribution of the spherical NPs and the resulting mechanical properties of the bimodal network. It is found that the NPs can be dispersed well, and a larger average distance between the NPs is realized with the increase of the length of the long polymer chains, the rigidity of short and long chains, and the temperature. There is a linear relationship between the average interparticle distance of NPs and the arithmetical average of the root-mean-square end-to-end distance of long and short chains. By adopting the uniaxial deformation, the stress-strain behavior and the bond orientation are examined. The results illustrate that introducing the short chains into the uniform long chains network can notably improve the tensile stress-strain performance. The bond orientation behaviors present that short chains are more prone to be oriented and stretched, contributing to more stress during the stretching process. Furthermore, enhanced stress-strain behaviors can be observed by manipulating the chain stiffness and temperature. Interestingly, the bimodal end-linked network reveals a distinctively enhanced stress-strain behavior versus the temperature, which is opposite to that of traditional physically mixed polymer nanocomposites (PNCs), attributed to a higher entropic elasticity and the uniform dispersion of NPs of the end-linked system at high temperatures. The network exhibits a linear relationship for the stress at a fixed strain versus the temperature. Notably, it is indicated that the contribution of entropy accounts for most of the total stress, while the change of internal energy only accounts for a small part, which is consistent with the experimental observation of the classic rubber elastic theory. In general, our study demonstrates a rational route to precisely control the spatial dispersion of the NPs and effectively tailor the mechanical properties of PNCs.

Interfacial anti-fatigue effect in graphene-copper nanolayered composites under cyclic shear loading

Low-cycle fatigue behaviors of graphene-copper nanolayered (GCuNL) composites are explored at different interface configurations and repeat layer spacings. The graphene interfaces can trap dislocations through impeding the propagation of dislocations in copper layers, giving rise to the absence of softening, and an increase in the fatigue strength of GCuNL composites (up to 400% that of pure copper). This anti-fatigue effect is independent of the crystal orientation of copper or the chirality of graphene due to interfacial constraints and can be controlled by tailoring the repeat layer spacing. Low repeat layer spacing increases the instability and nonlinearity of the composites, while high repeat layer spacing decreases the anti-fatigue effect. The optimum value of the repeat layer spacing for the GCuNL composites is 3-7 nm, in order to achieve a balanced anti-fatigue capability and interface stability.

Molecular insights into the effect of graphene packing on mechanical behaviors of graphene reinforced cis-1,4-polybutadiene polymer nanocomposites

We adopt molecular dynamics simulation to study the graphene packing patterns on chain structure, dynamics, uniaxial tension and visco-elastic behaviors.