On the Rheology of n-Eicosane

Abstract

We carry out non-equilibrium molecular dynamics (NEMD) simulations of liquid n-eicosane (C₂₀H₄₂) undergoing planar Couette flow. We show that a different rheological picture emerges if one uses the standard (but incorrectly formulated) ‘atomic’ thermostat rather than a thermostat which only couples to the centre of mass translational degrees of freedom. In the latter case eicosane shows shear thinning at low to moderate shear rates and then shear thickening at higher shear rates [G. P. Morriss, P. J. Daivis and Denis J. Evans, J. Chem. Phys., 94, 7420 (1991)]. However in the atomic thermostatted simulations, eicosane shows only shear thinning across the range of shear rates studied. Moreover in the atomic case, the eicosane molecules are more elongated and spin at a lower rate in the shear plane.

Key Words:

• Thermostats
• alkanes
• molecular dynamics
• shear