[SY-H5] Determination of mechanical properties of polymers from coarse grained molecular dynamics simulations: a few case studies
Polymers, by virtue of being synthetic, microscopically tailorable and light materials, are finding uses in challenging new technological situations. These new applications, involving high temperatures, harsh environments, impact, sustained dead loading and others, often demand changes in the macromolecular architecture. The ability to predict the effects of an architectural alteration on the ultimate mechanical behaviour of a bulk polymer is therefore, useful. Coarse grained molecular dynamics provide a route to conducting large and long simulations to establish structure property relationships in these materials. However, a wide variety of coarse graining methodologies exist and their suitability for obtaining mechanical properties needs to be systematically established before they can become effective predictive tools. In this talk, we will focus on our experience with coarse grained molecular dynamics simulations on long chained and crosslinked polymers. In particular, we will discuss, coarse graining strategies that rely on Boltzmann inversion based techniques for calibrating bonded interactions, and a variety of heuristic techniques targetting specific physical properties for the non-bonded. We will highlight the problems associated with simultaneously targetting multiple end properties like density, total energy and atomic virial. Moreover, the mismatch in time scales between detailed atomistic and coarse grained simulations and their influence on the rate dependent behaviour of properties like the glass transition temperature and uniaxial stress-strain response will also be discussed. Finally, we will demonstrate a few case studies on polystyrene and a group of crosslinked polyimides to show that coarse grained molecular dynamics simulations of polymers have good predictive capability and sometimes can provide useful insights into material behaviour.