RHEOLOGICAL BEHAVIOR OF CONCENTRATED SUSPENSIONS OF SOFT SPHERES

Rheological properties of concentrated suspensions of soft spheres hav e been studied in a concentration range where all the volume is filled by more or less swollen particles. The suspensions appear as soft gel s and show a dynamic modulus which is nearly frequency independent. Un der shear, an orientation of the deformed spheres at 45 degrees from t he velocity lines is observed. Since above a critical concentration, t he elastic modulus appears related to the intrinsic softness of the pa rticles, the modulus of the suspension has been calculated theoretical ly from a simple core-shell model of a swollen individual particle thr ough a minimization of the free energy. A satisfactory agreement is ob served with experimental data, using reasonable values of the fitting parameters.