Effects of Aggregation Degree and Cross-Linking Density on the Viscoelasticity of CNTs/CB-Filled Natural Rubber Composites: A Coarse-Grained Molecular Dynamics Simulation

Nanoparticle (NP)-filled natural rubber (NR) has garnered significant research interest because of its superior viscoelastic behavior. In this study, the effects of aggregation degree and cross-linking density on the viscoelasticity of carbon nanotubes (CNTs)/carbon black (CB)-filled NR composites are studied using coarse-grained molecular dynamics simulations. Dynamic shear simulation is conducted to calculate the storage modulus, loss modulus, and loss factor of the filled rubber. The simulation results demonstrate that CNTs dominate the dual-phase NP network composed of CNTs and CB. Meanwhile, the improvement of the aggregation degree of CNTs helps to increase the interaction between components and promote the formation of bound rubber. However, excessive dispersion of CNTs can reduce the interaction between CNTs, weaken the rigidity of the entire NP network, and reduce the formation of bound rubber, resulting in a decrease in storage modulus and a weakening of the Payne effect. In addition, the cross-linking structures of CNTs and NR also help to improve the storage modulus of the filled rubber and weaken the Payne effect of the filled rubber, which can be attributed to the enhanced interfacial rigidity and stability. The microstructure evolution of the composite network is analyzed in detail to reveal the synergistic mechanism of dual-phase NPs on the viscoelasticity of the filled rubber.