The phase separation behaviour and the viscoelastic properties of particles with non-adsorbing polymers:: Part II — Theoretical study

The high frequency shear modulus of a series of dispersions undergoing depletion interactions are modelled using a new depletion potential. This model gives rise to a net attraction between colloidal particles with added non-adsorbing polymer once a critical concentration is reached. This critical concentration is of the order of c*. The curvature of this potential allows the use of liquid state or cell models to predict the high frequency shear modulus. This requires a detailed knowledge of the polymer osmotic pressure as a function of concentration. This pressure has been derived from the elasticity and compared with a model for the pressure based on renormalisation group theory. The second Virial coefficient has been used as an adjustable parameter and the value used found to be in good agreement with experimental values for large values of aeff/Rg. The approach presented here highlights some of the difficulties in predicting the rheological properties for metastable depletion systems.