We are interested in understanding the role of particle deformability in the phase behavior and rheological properties of colloidal suspensions. In particular, we are studying the properties of dense ionic microgel suspensions. The particles are based on poly(vinylpyridine), which is a monomer that ionizes with pH, and a slight amount of divinylbenzene, a cross-linker. When de-swollen, the suspension exhibits liquid and crystal phases, and shear thins at high enough shear rates; the same behavior is obtained for swollen, but highly cross-linked particles. By contrast, when the microgels are swollen, the suspension does not crystallize, irrespective of the particle density, and does not exhibit shear thinning. This behavior is markedly different to that of ordinary colloids, in line with recent theoretical calculations [1], and suggests that the elasticity of the single particle can dramatically affect the phase behavior and mechanical properties of the packed suspension.

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[1] Gottwald, D.; Likos, C.N.; Lowen, H. Phys. Rev. Lett. 2004, 92, 068301.