Early NEMD simulations yielded an unexpected result: at high shear rates
) the viscosity decreased strongly,
to increase again at even higher .
(See, e.g. [Heyes et al., Mol. Phys. 57(1986)1265].)
This ``Non-Newtonian'' behaviour may indeed be observed
While a value of is unrealistically high for gases, it
is in an accessible range for liquids composed of large molecules, i.e.
this would mean
; then and with
Explanation: When becomes comparable to the thermal speed,
the molecules spontaneously arrange in flow lines that glide along each
other without interdiffusion. A plane perpendicular to the lines will
be crossed at points that form a hexagonal lattice.
At even higher shear the formation of vortices destroys the flow line
pattern, and the viscosity increaes again.
Heyes' results were later challenged and suspected of being computational
artefacts after all, the argument being that the specific method of
thermostating the sample was the source of trouble. As with Spring 2002
the issue seems unsettled.