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Alessio Zaccone: „Shear Elasticity of Dense Attractive Colloids: Homogeneous and Heterogeneous Glasses”
Institute for Chemical and Bioengineering, ETH Zurich, Switzerland

No satisfactory model is currently available to describe the elasticity of arrested colloids in relation to their structure and microscopic interaction. We have developed a theoretical elastic model for attractive arrested colloids and we have verified its predictions by means of molecular dynamics simulations. The model is not only able to quantitatively reproduce experimental results from the literature in the high density (homogeneous) glass regime (ca. 60% volume fraction), but it can also be combined with a hierarchic arrest scheme to successfully describe lower volume fraction regimes where structural heterogeneity plays an important role. In particular, this novel approach allows to discriminate the microscopic (primary-particle level) contribution from the mesoscopic (cluster-level) one in the case of (so-called) dense depletion gels. Thus we propose that arrested attractive colloids can be distinguished as homogeneous or heterogeneous colloidal glasses based on the length-scale by which, according to our model, their shear modulus is controlled. Whereas the characterization of structural heterogeneities requires detailed structural information and is therefore often elusive, the variation of this length-scale is unambiguously signalled by significant variation of the elastic modulus. Upon connecting the mechanical response to the structural features of these materials, our approach provides the missing information in one respect or the other and offers a new insight into the complex physics of arrested attractive colloids.