Séminaire Théorie

Mardi 21 Novembre 2017 à 11h00.

Aging and mechanical properties of poorly connected soft solids

''Self-assembly and aggregation of soft condensed matter like proteins, colloids or polymers into poorly connected and weakly elastic solids is very common and ubiquitous in nature. Phase separa- tion, spinodal decomposition as well as externally driven self-assembly or aggregation often lead to gels, which display diverse structures and solid-like mechanical features. The structural complexity of soft gels entails a versatile mechanical response that allows for large deformations, controlled elastic recovery and toughness in the same material. A limit to exploiting the potential of such materials is the insufficient fundamental understanding of the microstructural origin of the bulk mechanical properties, as well as their progressive aging over time. Investigating how different dynamical processes emerge at rest and how the mechanical response depend on the material microstructure will provide a new rationale, which would ultimately lead to several applications, ranging from improving the performance of batteries (colloidal gels), designing smart composites that can prevent the cascade of catastrophic events and can be used in anti-seismic buildings, and many with important biological function, such as new scaffolds for tissue engineering. In the first part of my talk, using numerical simulations of a minimal model, I will briefly present the cooperative dynamics emerging from the mesoscale organization of the network. The analysis of the gel restructuring at rest aims at disentangling the role of thermal fluctuations and the relaxation of the internal stresses closely reminiscent of various experimental observations. Then, I will present the link between the topology of the network and the non-linear rheological response: our analysis elucidates how the network connectivity alone could be used to modify the gel mechanics at large strains, from strain-softening to hardening and even to a brittle response. Reference: M. Bouzid et al., Nature Communications (2017)''