Origin of normal stress difference in consolidating strong depletion gels

In this study, we employ large scale numerical simulations complemented by a micromechanical model to investigate the consolidation process of a strong depletion gel. We clearly demonstrate that the origin of the normal stress difference in such depletion gel systems is a direct consequence of the mechanical anisotropy in the force networks, which cannot be captured by traditional continuum models that start with a stress-free reference state. The history-dependent nonlinear effects of prestress are better captured by tracking the evolution of essential state parameters, such as force anisotropy, mean normal force, and the average bond number, which govern different aspects of the consolidation process. A simple micromechanical constitutive relationship is proposed between the different stress tensor components and the internal state parameters, which is in excellent agreement with the simulation observations. Intriguingly, our findings strongly indicate the dominance of particle length scale phenomena in dictating the mechanical response of the consolidating depletion gel. This observation directly contradicts the existing literature's assumption, namely, that a characteristic cluster length scale larger than the particle length scale determines the mechanical response.