Concentration dependence of the linear elastic behaviour of model microgel dispersions

A model study of the linear viscoelastic behaviour of concentrated aqueous dispersions of deformable particles is described. Measurements on several grades of Sephadex beadlets with varying degrees of cross-linking were made in the linear range and demonstrated predominantly elastic behaviour. After allowing for differences in intrinsic swelling a universal concentration dependence was apparent. The detailed concentration dependence of the elastic modulus of the dispersions is consistent with a cell model with interparticle potentials given by Hertzian contact theory for elastic spheres. At very high concentrations, when swelling becomes restricted, the observed behaviour approaches that expected for deswelling of covalent gels with a scaling law exponent ≈0.6. The intrinsic elastic modulus of the granules inferred from the above cell model is in good agreement with independent estimates obtained from osmotic deswelling measurements on individual granules analysed according to Flory theory for cross-linked networks.