# Determination of pressure-viscosity relation of 2,2,4-trimethylhexane by all-atom molecular dynamics simulations

## TL;DR

This study uses all-atom molecular dynamics simulations to determine the pressure-viscosity relationship of 2,2,4-trimethylhexane at various pressures, providing insights into its rheological behavior under high-pressure conditions.

## Contribution

It introduces a high-pressure all-atom MD simulation approach with Eyring theory extrapolation to determine viscosity-pressure relations for hydrocarbons.

## Key findings

- Viscosity increases with pressure.
- Simulation results fit well to a common pressure-viscosity model.
- Extrapolated Newtonian viscosities at high pressures.

## Abstract

The Newtonian viscosity of 2,2,4-trimethylhexane at 293K is determined at pressures from 0.1MPa to 1000MPa. Non-equilibrium molecular dynamics simulations are performed using AIREBO-M, an all-atom potential for hydrocarbons especially parameterized for high pressures. The steady-state shear stress and viscosity are determined from simple shear simulations at rates between $10^7$ and $5\cdot 10^9\ \textrm{s}^{-1}$. At low pressures, simulation rates are low enough to reach the Newtonian regime. At high pressures, results are extrapolated to the Newtonian limit by fitting rate-dependent viscosities to Eyring theory. The resulting pressure dependent viscosity is typical of small molecules and fits to a common model are discussed.