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This work is concerned with the determination of the effective particle−particle interaction in colloidal suspensions from rheology. In particular, a concentrated microgel suspension is considered, in which particles interact through a repulsive polymer−polymer potential. The rheological modeling of this suspension was carried out by the authors in a recent work. Here, the interaction potential provided by that model is compared with the ones resulting from different models found in the literature. In this sense, a series of approaches relating the pair potential to rheological data such as dynamic modulus, viscosity, and yield stress is examined. Then the results of applying these models to experimental data are discussed, showing the advantages and limitations of each approach for the particular case of concentrated microgel suspensions. de Gennes' theoretical pair potential for polymer-covered particles is also included for comparison. The proposed viscosity model appears rather general and it is expected to have success in determining the effective potential in colloidal systems with different particle−particle force laws.

The rheological behavior of suspensions containing cross-linked polymer particles (microgels) was studied. Under flow, these particles behave as soft spheres due to the shear-induced deformability of their external polymeric layer and the suspensions are strongly shear-thinning. At concentrations where particles are densely packed, the suspensions present a solidlike behavior involving elasticity and yield stress. The rheological modeling of such suspensions was based on the concept of the effective volume fraction of particles, which depends on hydrodynamic forces. In this sense, microgel particles were assumed to have a simple core−shell configuration and to interact through a repulsive polymer−polymer potential. The viscosity equation resulting from the modeling allows:  (a) appropriate correlation of the experimental data shear stress versus shear rate in steady shear flow and (b) accounting for the softness of particles, which changes with concentration and shear stress. Also the predictions of the model showed to be quite consistent with results obtained previously for the same suspensions through different techniques such as dynamic rheometry and rheoptics.