Coarse-Graining of Chain Models in Dissipative Particle Dynamics Simulations

We have examined the influence of coarse-graining polymer chains in dissipative particle dynamics simulations on both phase behavior and aggregation dynamics. Our coarse-graining approach involves replacing several beads of a chain with a single bead of larger size and mass, and extends a framework recently developed by Backer et al. [J. Chem. Phys. 2005, 123, 114905] The parameters governing the interactions between particles are determined on the basis of conserving the number of interactions per particle, mass density, pressure, and shear viscosity of the original reference system. Phase diagrams of coarse-grained polymer/solvent systems are conserved, aside from a simple vertical shift in the direction of a(12), the repulsion parameter between solvent and polymer particles. The dynamics of the aggregation process are well conserved upon coarse-graining in a diblock copolymer/solvent system. We find that the invariance of the phase diagrams and aggregation dynamics occurs when the molecular volume of each species is conserved upon coarse-graining. However, this suggests that our coarse-graining approach cannot be applied to a monomeric solvent, in which case each solvent molecule already has the minimum number of degrees of freedom. Our results suggest that considerable freedom exists for selection of mapping ratios from real monomer units to model beads in dissipative particle dynamics simulations of chains in a solvent.