Rheological behaviour of concentrated suspensions of soft spheres

Rheological properties of concentrated suspensions of soft spheres have been studied in a concentration range where all the volume is filled by more or less swollen particles. The suspensions appear as soft gels and show a dynamic modulus which is nearly frequency independent. Under shear, an orientation of the deformed spheres at 45 degrees from the velocity lines is observed. Since above a critical concentration, the elastic modulus appears related to the intrinsic softness of the particles, the modulus of the suspension has been calculated theoretically from a simple core-shell model of a swollen individual particle through a minimization of the free energy. A satisfactory agreement is observed with experimental data, using reasonable values of the fitting parameters.