Exploring the ability of a multiscale coarse-grained potential to describe the stress-strain response of glassy polystyrene
Thomas W. Rosch, John K. Brennan, Sergei Izvekov, and Jan W. Andzelm
Accepted
A new particle-based bottom-up method to develop coarse-grain models of polymers is presented and applied to polystyrene. The multi-scale coarse graining (MS-CG) technique of Izvekov et al. [J. Chem Phys. 120, 10896 (2004)] is applied for the first time to a polymer system to calculate nonbonded interactions. The Inverse Boltzmann Inversion (IBI) method was used to parameterize the bonded and bond-angle bending interactions. Molecular dynamics simulations were performed, and the CG model exhibited a significantly lower modulus compared to the atomistic model at low temperature and high strain rate. In an attempt to improve the CG model performance, several other parameterization schemes were used to build other models from this base model. The first of these models included standard frictional forces through use of the constant-temperature dissipative particle dynamics (DPD) method that improved the modulus, yet was not transferrable to higher temperatures and lower strain-rates. Other models were built by increasing the attraction between CG beads through direct manipulation of the nonbonded potential, where an improvement of the stress response was found. For these models, two parameterization protocols that shifted the force to more attractive values were explored. The first protocol involved a uniform shift, while the other protocol shifted the force in a more localized region. The uniformly-shifted potential greatly affected the structure of the equilibrium model as compared to the locally-shifted potential, yet was more transferrable to different temperatures and strain-rates. Further improvements in the coarse-graining protocol to generate models that more satisfactorily capture mechanical properties are suggested.