Fully Atomistic Molecular Dynamics Computation of Physico-Mechanical Properties of PB, PS, and SBS

The physical properties-including density, glass transition temperature (T_g), and tensile properties-of polybutadiene (PB), polystyrene (PS) and poly (styrene-butadiene-styrene: SBS) block copolymer were predicted by using atomistic molecular dynamics (MD) simulation. At 100 K, for PB and SBS under uniaxial tension with strain rate ε ˙ = 10¹⁰ s^-1 and 10⁹ s^-1, their stress-strain curves had four features, i.e., elastic, yield, softening, and strain hardening. At 300 K, the tensile curves of the three polymers with strain rates between 10⁸ s^-1 and 10¹⁰ s^-1 exhibited strain hardening following elastic regime. The values of Young's moduli of the copolymers were independent of strain rate. The plastic modulus of PS was independent of strain rate, but the Young's moduli of PB and SBS depended on strain rate under the same conditions. After extrapolating the Young's moduli of PB and SBS at strain rates of 0.01-1 s^-1 by the linearized Eyring-like model, the predicted results by MD simulations were in accordance well with experimental results, which demonstrate that MD results are feasible for design of new materials.