Subventions et des contributions :

Subvention ou bourse octroyée s'appliquant à plus d'un exercice financier. (2017-2018 à 2022-2023)

This research program employs theory and computer simulations to explore the mechanical behavior of structurally disordered and polymeric matter far from equilibrium. Examples of disordered materials include amorphous metals, many soft glasses such as foams, pastes, emulsions, and dense colloidal suspensions or cell assemblies. In these materials, deformation mechanisms are much less understood than in crystalline solids, where the motion of defects as carriers of plastic flow is easily identified. Existing engineering descriptions tend to focus on average behavior and fail when fluctuations become large. Here we seek a fundamental understanding of the microscopic origin of the rheological behaviour of amorphous metals and yield stress fluids in order to be able to tune and improve their mechanical properties. The rheological flow rules governing stress and strain rate are not only strongly nonlinear, but also imply spatial nonlocal cooperativity when the material yields. This cooperativity leads to the localization of deformation into shear bands, which currently precludes widespread applications of metallic glasses. Here, we will connect molecular simulations on the particle scale quantitatively with coarser descriptions on mesoscopic and continuum scales to construct a predictive statistical theory of plastic flow of amorphous matter.

Additionally, we will innovate new computational tools for simulating structure and mechanics of nanostructured macromolecular networks with transient (i.e. physical) crosslinks. Common examples are thermoplastic elastomers formed out of copolymers or semicrystalline polymers, which have widespread consumer and industrial applications. We will analyze deformation processes at chain level with molecular simulations connecting different length and time scales in order to develop and test theoretical models that can translate molecular structure into mesoscale morphology, and then predict macroscale properties. An important part will be to investigate breaking of soft elastomers with self-healing capabilities via physical mechanisms such as hydrogen bonds or phase separation. We will compute the structure, viscoelasticity, and fracture of smart (stimuli responsive) hydrogels based on thermosensitive (co)polymers, which find applications as actuators, artificial tissue or medical implants. In a model for semiflexible biological hydrogels representing the cytoskeletal network of living cells, we will explore the propagation of the elastoplastic response to local perturbations, which is believed to play an important role in cell signaling. Elucidating pathways to controlled assembly and response of elastomers and hydrogels enables computationally-informed accelerated design of new materials and better understanding of the emerging properties of active matter.