(211g) Structure and Mechanical Properties of Attractive Colloidal Gels and Glasses

Zaccone, A., ETH Zurich
Wu, H., Institute for Chemical and Bioengineering
Morbidelli, M., Institute of Chemical and Bioengineering, ETH Zurich

By means of a scaling approach, we investigated the elasticity and microstructure of depletion gels and attractive colloidal glasses. The former can be considered as a low-density extension of the latter ones as suggested by both theoretical and experimental studies in recent years. Thus, it is natural to model the elasticity of depletion gels based that of attractive colloidal glasses. We adapted our recently developed free energy expansion approach for the elasticity of disordered aggregates of colloids to the case of depletion gels and found that the shear modulus as a function of volume fraction as measured by other authors can be predicted by our analytical model without any free parameters provided the system, in terms of attraction parameters, is quenched well below the spinodal line. By contrast, for the same data, the mode-coupling theory leads to overestimation of the moduli by two orders of magnitude. However, for weak-link networks just above or along the spinodal line anharmonic terms in the elastic energy expansion as well as non-affinity become important and only mode-coupling theory can reproduce the experimental scaling with volume fraction. These results provide a framework to predict the mechanical properties of technologically important materials such as attractive colloidal glasses and dense gels and support the emerging unifying picture for the structure-properties relation in disordered attractive systems.