Dissipative particle dynamics simulations of a single isolated polymer chain in a dilute solution.

In this study, we investigate the suitability of dissipative particle dynamics (DPD) simulations to predict the dynamics of polymer chains in dilute polymer solutions, where the chain is represented by a set of beads connected by almost inextensible springs. In terms of behaviour, these springs closely mimic rods that serve as representations of Kuhn steps. We find that the predictions depend on the value of the repulsive parameter for bead-bead pairwise interactions used in the DPD simulations ($a_{ij}$). For all systems, the chain sizes and the relaxation time spectrum are analyzed. For $a_{ij} = 0$, theta solvent behaviour is obtained for the chain size, whereas the dynamics at equilibrium agrees well with the predictions of the Zimm model. For higher values of $a_{ij}$, the static properties of the chain show good solvent behaviour. However, the scaling laws for the chain dynamics at equilibrium show wide variations, with consistent results obtained only at an intermediate value of $a_{ij} = 25$. At higher values of the repulsive parameter ($a_{ij} \geq 25$), our simulations are also able to predict the abrupt cut-off in the relaxation spectrum, which has been observed earlier in experiments of dilute solutions. The cut-off reached an extent that, for chain lengths of 10 Kuhn steps, the spectrum consists of a single time scale. This agrees remarkably well with earlier experiments and MD simulations. To verify further, we also studied the chain dynamics in shear flow using DPD simulations. Specifically, we analysed the variation of the chain stretch and end-over-end tumbling with shear rates. Overall, the trends obtained from DPD simulations agree well with those observed in earlier BD simulations.