NEMD INVESTIGATION OF THE RHEOLOGY OF OBLATE MOLECULES - SHEAR-FLOW IN LIQUID BENZENE

We employ a recently developed refinement of the computer-simulation algorithm of Edberg, Evans and Morriss to study the rheology of liquid benzene. This is the first simulation study of the rheology of oblate, or disc-like, molecules. We study shear-induced molecular order (shear birefringence) and molecular rotation (the Born effect) and their effect on the shear viscosity of liquid benzene. Our data clearly show that in the linear regime the benzene molecules preferentially align their sixfold rotation axes in the shear plane, at 135° to the streamlines. In this same regime the average angular velocity of the benzene molecules is equal to half the strain rate (ω2 = 1/2δux/δy). As the strain rate increases, the fluid at first shear-thins, with the average angular velocity decreasing and the alignment angle decreasing from 135° towards 90°. At very high strain rates the fluid shear thickens, the alignment angle becomes quite close to 90° (so that the plane of the benzene ring is nearly parallel to the streamlines), but the average intrinsic angular velocity increases, again approaching the Born value (ω2 = 1/2δux/δy). © 1990 Taylor & Francis Group, LLC.