Shear modulus of colloidal suspensions: Comparing experiments with theory

In this work, the experimentally determined shear modulus of a colloidal suspension has been compared to a calculated shear modulus based on an ordered lattice model. The experiments were performed on a well characterized calcite suspension. The calcite suspension was confirmed to be in a flocculated state, thus exhibiting strong elastic character. The experimental shear modulus was estimated from the elastic modulus in the linear viscoelastic region. This is contrary to established convention, where the high frequency limiting modulus is used. However, the network structure breaks down at high frequencies, resulting in a different system. Therefore the shear modulus was estimated from the response of the intact particle network structure, which resides within the linear viscoelastic region. Calculation of the shear modulus is based on an ordered lattice model, where the particles are arranged in regular 3D-arrays. Interaction forces between the particles are also considered, based on the well known DLVO-theory. Calculations of the shear modulus for flocculated colloidal suspensions are not trivial however, because of the random distribution of particles. Due to this fact the average interparticle distance is impossible to determine exactly and therefore the comparison between experimental and calculated shear modulus was made by calculating the shear modulus as a function of interparticle separation. Some different models for interaction forces between particles were tried, and the results were compared to rheological data. These preliminary results show that useful suspension properties can be evaluated by combining rheological measurements with theories for interactions between particles arranged in ordered lattices.