Non-Newtonian behaviors of simple fluids by molecular dynamics simulations

The non-Newtonian behaviors of two typical simple fluids, LJ fluids and hard sphere gases, are studied using molecular dynamics simulations. Both Couette and oscillatory shear flows are investigated. In the steady shear flow, both the LJ fluid and hard sphere gas exhibit shear thinning at high shear rates. In the oscillatory flows, phase lags of the shear strain rates behind the shear stresses are observed at extreme high frequencies and the phase differences increase with frequency for both the LJ fluid and hard sphere gas. As for the physical mechanism, the changes of the pair radial distribution function and potential energy of the LJ fluid are observed at high shear rates. However, as hard sphere gases have no potential energies and fixed molecular configuration, the traditional theory cannot interpret the non-Newtonian phenomena of hard sphere gases. From the viewpoint of the recent kinetomass theory, the inertia effect of kinetomass (equivalent mass of transferred energy) can account for the non-Newtonian behaviors of simple fluids.