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 depl etion 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 c oncentration 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 el asticity and compared with a model for the pressure based on renormalisatio n group theory. The second Virial coefficient has been used as an adjustabl e parameter and the value used found to be in good agreement with experimen tal values for large values of a(eff)/R-g. The approach presented here high lights some of the difficulties in predicting the rheological properties fo r metastable depletion systems. (C) 2000 Elsevier Science B.V. All rights r eserved.