Comparison of equilibrium techniques for the viscosity calculation from DPD simulations

Area of Science:

• Computational physics and chemistry
• Mesoscopic fluid dynamics modeling
• Polymer science

Background:

• Dissipative Particle Dynamics (DPD) is a mesoscopic simulation technique widely used for fluid morphology and structure prediction.
• The accuracy of DPD for calculating the viscosity of complex fluids, such as polymer solutions, remains an area of investigation.

Purpose of the Study:

• To evaluate the capability of DPD simulations in accurately determining the viscosity of unentangled polymer solutions.
• To compare the efficiency and accuracy of the Einstein and Green-Kubo formulas for viscosity estimation in DPD.
• To introduce a revised Einstein relation for enhanced statistical accuracy.

Main Methods:

• Estimation of viscosity using both Einstein and Green-Kubo formulas within DPD simulations.
• Derivation of a revised Einstein relation analogous to the Jung and Schmid Green-Kubo formula.
• Simulation of unentangled polymer solutions with varying conservative and friction parameters.

Main Results:

• DPD simulations successfully reproduced theoretical dynamical behavior, irrespective of parameter choices.
• The revised Einstein method achieved comparable statistical accuracy to the Green-Kubo formula with shorter simulation trajectories.
• A Schmidt number consistent with fluid systems was estimated.

Conclusions:

• DPD simulations are a reliable method for calculating the viscosity of complex fluids.
• The revised Einstein formula enhances the statistical accuracy of viscosity calculations, particularly for shorter simulation times.
• This study validates DPD for complex fluid viscosity prediction and offers an improved methodology.