Predicting the Rheology of Complex Fluids

Abstract

Progress towards the absolute prediction of the constitutive rheological relations of more complex fluids using the methods of non-equilibrium molecular/particulate dynamics simulations is reviewed. The approaches are based upon the initial use of simple hard-, soft-, and colloidal-sphere effective pair potentials and corresponding state scaling analyses. The general objective is illustrated initially using results for the soft-sphere fluid viscosity, and soft-sphere scaling laws to predict the Newtonian viscosities of simple molecular liquids and gases for physical data banks. It is further shown how the non-Newtonian behaviour of these simple hard- and soft-sphere models can be scaled to predict the flow curves of colloidal suspensions when the models and equations-of-motion are appropriately modified or scaled to take account of the mean hydrodynamic flow field, solvation and/or Brownian motion effects of the medium.

Preliminary extensions towards the prediction of dry powder flow using methods of granular dynamics are also reported: the collisional dynamics are damped by an effective coefficient of restitution which leads to similar scaling laws; gravitational scaling units may also be used in this case.

Key Words:

• Rheology
• complex fluids
• non-equilibrium molecular dynamics
• soft-spheres
• scaling laws