Abstract
An optimized Dissipative Particle Dynamics (DPD) model with simple scaling rules was developed for simulating entangled linear polyethylene melts. The scaling method, which can be used for mapping dimensionless (reduced units) DPD simulation data to physical units, was based on scaling factors for three fundamental physical units; namely, length, time, and viscosity. The scaling factors were obtained as ratios of equilibrium Molecular Dynamics (MD) simulation data in physical units and equivalent DPD simulation data for relevant quantities. Specifically, the time scaling factor was determined as the ratio of longest relaxation times, the length scaling factor was obtained as the ratio of the equilibrium end-to-end distances, and the viscosity scaling factor was calculated as the ratio of zero-shear viscosities, each as obtained from the MD (in physical units) and DPD (reduced units) simulations. The scaling method was verified for three MD/DPD model liquid pairs under several different nonequilibrium conditions, including transient and steady-state simple shear and planar elongational flows. Comparison of the MD simulation results with those of the scaled DPD simulations revealed that the optimized DPD model, expressed in terms of the proposed scaling method, successfully reproduced the computationally expensive MD results using relatively cheaper DPD simulations.
Highlights
An optimized Dissipative Particle Dynamics (DPD) model with simple scaling rules was developed for simulating entangled linear polyethylene melts
The development of simple and accurate rescaling parameters through adequate mapping of DPD results to corresponding Molecular Dynamics (MD) results could lead to significant advantages in the realistic and reliable analysis of the dynamics of polymeric liquids using computationally affordable methods such as DPD
A simple and accurate method was developed to rescale equilibrium and nonequilibrium DPD simulation data, which are naturally dimensionless, to physical units that are consistent with those obtained from equivalent atomistic MD simulations of model linear entangled polyethylene liquids
Summary
An optimized Dissipative Particle Dynamics (DPD) model with simple scaling rules was developed for simulating entangled linear polyethylene melts. Coarse-grained models of atomistic liquids offer a more computationally tractable alternative to brute force MD simulations wherein individual atomistic molecular units are grouped together and treated as single entities, greatly reducing the number of degrees of freedom to be tracked during the time integration Mesoscale simulation methods, such as SL, SS, and DPD, have contributed significantly to the understanding of linear and nonlinear rheology of entangled fluids at length and time scales beyond the computational limitations of MD simulations. The accuracy of DPD simulations is directly related to how accurately various static and dynamic properties of the chain (as determined via atomistic simulations) can be used to determine the time and length scales of the associated multiatomic particles of the DPD simulations To this end, attention is focused on developing an accurate yet simple method to obtain rescaling parameters such that DPD and MD simulation results are fully consistent over a wide range of deformation rates in common flow situations, such as steady-state and startup of shear and elongational flows
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