Quantitatively predicting the mechanical behavior of elastomers via fully atomistic molecular dynamics simulation

Employing computer simulation to accurately and quantitatively predict the mechanical properties of polymeric materials is a long-standing challenge. Herein, we consider two methods to simulate the mechanical properties based on a fully atomistic model of crosslinked styrene-butadiene rubber (SBR) network via molecular dynamics simulation. In the first method (stepwise deformation and relaxation), by keeping the tensile velocity constant and regulating the simulation time that each deformation period takes, sufficient relaxation occurs in the consecutive deformation, which enables each deformation period followed by a corresponding relaxation period. The engineering stress-strain curve finally obtained by this stepwise deformation and relaxation method exhibits similar features of elastomers compared with the experimental results. The second method divides the whole deformation process into several discontinuous parts. Sufficient relaxation also occurs in several independent SBR systems at the specific strain and the relaxed stress plateau is indicated to represent the stress that SBR system exhibits at specific strain after allowing the system to relax. Compared with the traditional uniaxial tensile method (continuous deformation in constant strain rate) and the first method we adopt, the second method could also characterize the mechanical behavior of elastomers and improve the computational capability on the level of a large-scale system. Compared with the excessively large values obtained by traditional method, the elastic modulus, the modulus at 100 %, 300 % and 500 % of the full atomistic SBR are calculated as 38.5 MPa, 12.0 MPa, 25.1 MPa and 83.1 MPa, respectively, which exhibits more realistic mechanical behavior and merely exceeds around one order of magnitude than the experimental results. These methods are believed to serve as a good basis for further accurately simulating and predicting the mechanical properties of elastomers.