Study of arbitrarily low shear rate rheology using dissipative particle dynamics

TL;DR

This paper demonstrates that the transient time correlation function (TTCF) technique enables accurate rheology measurements at arbitrarily low shear rates in dissipative particle dynamics (DPD) simulations, overcoming previous high shear rate limitations.

Contribution

The study adapts and validates the TTCF method for DPD systems, allowing low shear rate rheology measurements with improved accuracy and without the need for trajectory mappings.

Findings

TTCF yields lower standard error than classic averaging across shear rates.

SNR remains constant at low shear rates using TTCF.

Mapping is unnecessary for accurate TTCF-based viscosity calculations.

Abstract

The use of dissipative particle dynamics (DPD) simulation to study the rheology of fluids under shear has always been of great interest to the research community. Despite being a powerful tool, a limitation of DPD is the need to use high shear rates to obtain viscosity results with a sufficiently high signal-to-noise ratio (SNR). This often leads to simulations with unrealistically large deformations that do not reflect typical stress conditions on the fluid. In this work, the transient time correlation function (TTCF) technique is used for a simple Newtonian DPD fluid to achieve high SNR results even at arbitrarily low shear rates. The applicability of the TTCF on DPD systems is assessed, and the modifications required by the nature of the DPD force field are discussed. The results showed that the standard error (SE) of viscosity values obtained with TTCF is consistently lower than that of the classic averaging procedure across all tested shear rates. Moreover, the SE resulted proportional to the shear rate, leading to a constant SNR that does not decrease at lower shear rates. Additionally, the effect of trajectory mapping on DPD is studied, and a TTCF approach that does not require mappings is consolidated. Remarkably, the absence of mappings has not reduced the precision of the method compared with the more common mapped approach.