RHEOLOGICAL PROPERTIES OF THIN LIQUID-FILMS BY MOLECULAR-DYNAMICS SIMULATIONS

In this paper we present the molecular dynamics simulations of thin fl uids films sheared in Couette flow geometry between two structured pla ne walls. An NVT ensemble of atoms was chosen and simulation conducted in isothermal conditions. To keep the temperature at the required lev el a Gaussian thermostat was employed. This method was shown to be sup erior to the simple velocity rescaling method, especially at high shea r rates. The Gaussian thermostat method gave results for viscosity in good agreement with the results of other researchers who used the rese rvoir method. The results for density and velocity profiles were obtai ned for a wide range of simulation parameters. The effects of shear ra te and wall-fluid interaction strength were investigated in detail ove r a wide range of parameters. The material functions and normal stress differences were also obtained and the effects of shear rate and wall strength parameter on these properties were studied. The effect of fi lm thickness on the viscosity was investigated and was compared with w hat we found for bulk fluid using the SLLOD algorithm. the existence o f a non-Newtonian region with shear-thinning effect is found and exami ned for various films. The results suggest an increase in viscosity fo r thinner films in the Newtonian regime, though this is valid only for a limited range of wall-fluid interaction strength. A decrease in vis cosity was also observed when the attraction force of the wall was inc reased. (C) 1997 Elsevier Science B.V.