ON THE RHEOLOGY OF N-EICOSANE

We carry out non-equilibrium molecular dynamics (NEMD) simulations of liquid n-eicosane (C20H42) undergoing planar Couette flow. We show tha t a different rheological picture emerges if one uses the standard (bu t incorrectly formulated) 'atomic' thermostat rather than a thermostat which only couples to the centre of mass translational degrees of fre edom. In the latter case eicosane shows shear thinning at low to moder ate 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 (1 991)]. 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 spi n at a slower rate in the shear plane.