# A non-empirical free volume viscosity model for alkane lubricants under severe pressures

## TL;DR

This paper develops a non-empirical, microscopic free volume viscosity model for alkane lubricants under severe pressures, combining molecular dynamics data with theoretical concepts to accurately predict viscosity without empirical parameters.

## Contribution

It introduces a parameter-free viscosity model based on equilibrium molecular dynamics and microscopic ensemble averages, applicable to high-pressure alkane lubrication.

## Key findings

- Accurately predicts viscosity and diffusion coefficients at high pressures and temperatures.
- Provides a microscopic basis for viscosity modeling without empirical fitting.
- Enhances understanding of alkane lubricant behavior under severe conditions.

## Abstract

Viscosities $\eta$ and diffusion coefficients $D_s$ of linear and branched alkanes at high pressures $P$$<$0.7 GPa and temperatures $T$=500-600 K are calculated by equilibrium molecular dynamics. Combining Stokes-Einstein, free volume and random walk concepts results in an accurate viscosity model $\eta(D_s(P,T))$ for the considered P and T. All model parameters (hydrodynamic radius, random walk step size and attempt frequency) are defined as microscopic ensemble averages and extracted from EMD simulations rendering $\eta(D_s(P,T))$ a parameter-free predictor for lubrication simulations.