Role of structural disorder in dense particle systems: from amorphous materials to active matter

28.09.2021 13:00 – 14:30

Disorder is ubiquitous is physical systems, and can radically alter their physical properties compared to their ‘pure’ counterparts. For instance, ferromagnetic materials can be used as magnetic memories in our computers’ hard drives only because of the presence of impurities in their crystalline structure: the latter allow for the ‘pinning’ of the ferromagnetic domain walls between digital bits, and the resulting stability of these memories. A very large class of systems lies on the opposite limit where there is no crystalline structure to start from at all: emulsions as mayonnaise, foams, or metallic glasses are all structurally disordered, and this has key implications for their rheological, mechanical or transport properties.

There has been recently many attempts to relate the important corpus of known results for such ‘passive' amorphous materials, and their counterparts in active matter such as confluent biological tissues. One strong motivation is that the interplay between activity and structural disorder might in turn be related to biological functionalities. Here I will discuss two studies performed in that spirit, at a mean-field level. In [1], we compared the mechanical response between sheared granular material and active matter, in the glassy phase where they behave as ’solids'. We were in particular able to establish a direct equivalence between a global forcing (external shear) and a random local forcing (reminiscent of active matter), upon a simple rescaling of the control parameter (the accumulated strain). In [2] we examine how the activity stemming from the apoptosis and division rate in a model biological tissue can on the contrary fluidise these materials, resulting in the non-linear rheology of a ‘complex fluid’.


[1] « A direct link between active matter and sheared granular systems », P. Morse*, S. Roy*, E. Agoritsas*, E. Stanifer, E. I. Corwin, and M. L. Manning, PNAS 118, e2019909118 (2021).

[2] « Nonlinear Rheology in a Model Biological Tissue », D. A. Matoz-Fernandez*, E. Agoritsas*, J.-L. Barrat, E. Bertin, and K. Martens, Phys. Rev. Lett 118, 158105 (2017).

Lieu

Bâtiment: Ecole de Physique

Auditoire Stückelberg

entrée libre