NONEQUILIBRIUM MOLECULAR AND BROWNIAN DYNAMICS SIMULATIONS OF SHEAR THINNING OF INVERSE POWER FLUIDS

The shear thinning behaviour is compared of model atomic and colloidal liquids computed using molecular dynamis (MD) and Brownian dynamics (ED) simulations, respectively. Apart from the equations of motion, other quantitative features of the two models are identical. Using an internal standard time scale, derived from the integral of the normalized linear stress relaxation function, it is shown that there are significant differences in the normalized shear thinning curves and the associated assembly restructuring under shear of the two model liquids. The hexagonal string phase appears approximately at a value of half shear thinning for the MD system, whereas the ED liquid manifests the string phase only at much higher equivalent shear rates at the onset of the second Newtonian plateau. These differences are explained in terms of the more 'sluggish' dynamics of the model colloidal system, derived from their inertialess equations of motion. Other thermodynamic and mechanical properties of the model liquids are shown to reflect the relative reluctance of the ED liquid to form the string phase, when compared with the MD liquid.