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Equilibrium and non-equilibrium molecular dynamics techniques are used to simulate a molecular liquid (n-hexadecane) at extreme physical conditions (high temperatures, pressures and shear rates), typical of those encountered in many elastohydrodynamic lubrication applications, and to study the effects of pressure and temperature on the calculated rheological properties. Pressure and temperature effects are found to be more pronounced at low shear rates than at high shear rates, where the non-Newtonian behaviour is dominated by the strong external kinematic effects. The observed non-Newtonian behaviour of the pressure and temperature coeficients of viscosity and the variation of certain molecular geometric functions calculated to assist the microscopic understanding are combined to provide a possible explanation for the phenomenon of limiting shear stress under elastohydrodynamic lubrication conditions. Further implications for the behaoiour of lubricant-like molecules in practical applications are also discussed.

Dissipative particle dynamics (DPD) originated as a tool for performing fluid dynamics simulations of complex fluids and amongst other things has been used to simulate dilute polymer solutions. The technique employed an Euler time-stepping technique up until recently, when a velocity-Verlet type algorithm was proposed. This paper presents a more accurate velocity-Verlet and analyses the equilibrium properties of this new technique for finite time-steps. An expression for the temperature in terms of the basic DPD parameters is derived for this scheme. Int. J. Mod. Phys. C 1999.10:241-261. Downloaded from www.worldscientific.com by FLINDERS UNIVERSITY LIBRARY on 02/07/15. For personal use only.

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