Influence of Temperature and Pressure on Dynamics and Viscoelasticity of Styrene Butadiene Rubber: Insight from Molecular Dynamics Simulation.

Abstract

In this work, the dynamics and viscoelasticity of styrene butadiene rubber (SBR) are systematically explored for different temperatures (T) and pressures (P), where the coarse-grained model and potential functions are developed by the iterative Boltzmann inversion approach. The simulation results reveal that the dynamics at the monomer and chain scales display different dependencies on T and P. Thus, a time-T-P superposition principle (TTPSP) holds at both the monomer and chain scales for the translational dynamics. However, TTPSP fails at the monomer scale for the relaxation dynamics while remaining valid at the chain scale at a high T. Meanwhile, a low T enhances dynamical heterogeneity, while a high P reduces fragility, which also reduces the monomer mobility. The universal correlations among the relaxation time, corresponding peak height, Debye-Waller factor, T, and P are derived. These indicate the reduced anisotropy of cage shapes at a high P value and some decoupling or coupled relationships. Finally, the storage modulus, loss modulus, and viscosity of SBR are analyzed, which exhibit a gradual increase with decreasing T or increasing P. Interestingly, the viscoelastic properties present a strong relationship with local chain stiffness. TTPSP holds for viscoelasticity at a high T, while it breaks down over the entire T range, which mainly originates from the complex multiscale dynamical behavior of SBR. In summary, this work provides a comprehensive understanding of how temperature and pressure influence the dynamics and viscoelasticity of the SBR.