Elastic, viscoelastic, dynamic, topological and structural properties of crosslinked SBR through atomistic molecular dynamics simulations

In this research work, we provide a detailed investigation of the structural and viscoelastic properties of crosslinked styrene butadiene rubber (SBR) networks that are studied using atomistic molecular dynamics simulations. The composition of the system ratio is (styrene/<i>trans</i>/vinyl/<i>cis</i>): (15/33/26/26) by weight and a 4-atom sulfur chain was used as a hardener for the crosslinking process. The main goal of our work is to characterize a fully percolated SBR network, with a crosslinking density of 8%, at the molecular level, structurally, mechanically and topologically and compare its properties with a system with a lower crosslinking density (3%) and the non crosslinked SBR melt. SBR crosslinked systems are generated <i>via</i> a recently proposed crosslinking algorithm. The shear stress relaxation modulus and the mean square displacement (MSD) were calculated for all systems along with structural properties, such as the pair distribution function, angles and dihedral distributions, and statistical distributions of the atoms between the crosslinks, and finally the topology of these networks was investigated according to the number of clusters that are created during the different crosslink densities, the molecular weight fraction of the largest cluster in these networks, and finally the percolation threshold. The results indicate that the higher we crosslink the SBR, the stiffer our final rubber becomes according to the results of the dynamics and rheology. We further probe the dependence of the structural and viscoelastic properties of the SBS rubber on crosslinking density by comparing a fully percolated system with one having lower crosslinking density (3%) and the non crosslinked SBR melt.