Development of Enhanced Interactions for Highly Coarse-Grained Materials

Abstract Modelling micro- and mesoscale transport of soft condensed matter hinges upon its representation, including any complex phenomena, at appropriate length and time scales, especially when using larger-than-atomistic techniques such as dissipative particle dynamics (DPD). Simple repulsive pairwise interactions typically used in DPD calculations can capture some complexity, but certain thermodynamic behaviours such as single-component phase coexistence and transitions are normally unavailable. By extending the commonly-used DPD interactions to include attraction and additional control on repulsion, we have devised a new interaction model for highly coarse-grained and mesoscopic scales. The model, denoted here as nDPD, retains many advantages of the original while enabling more complex thermodynamic behaviours, particularly vapour-liquid coexistence below a critical point and solid-liquid transitions. Some of its features include: changes in liquid curves for vapour-liquid coexistence based on repulsion steepness, comparatively low melting points, contraction of solid phases upon heating (negative thermal expansion) and pressure-induced melting. Here, we demonstrate how nDPD can be parameterised for highly coarse-grained water, and how well it fits potentials for long polymeric chains that have been systematically coarse-grained from atomistic molecular dynamics calculations. These enable further exploration of these materials in the rheological domain using DPD-based modelling.