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Seminaire Interne
Par Anis Senoussi / Ananyo Maitra
Le 27 Novembre 2018 à 11h00 - Salle de séminaires 5ème étage, Tour 32-33


Maitra : Can orientational order be sustained in highly active systems?


It is generally believed that orientationally ordered phases of active particles in fluids are generically destabilised by activity. However, I will demonstrate that activity can at times stabilise ordered phases. I first reexamine the standard theory of apolar suspensions on substrates and uncover a hitherto overlooked active force with a distinct spatial symmetry. This active force, which I show is more relevant compared to the usual one at large scales, can lead to an ordered state which becomes more stable with increasing activity. I then examine a novel active phase of synchronously rotating chiral active particles and demonstrate that in this case, the spontaneous rotation can stabilise the ordered phase even in momentum conserved systems. These results can explain the unusual stability of ordered phases in certain bacterial and motor-microtubule systems.


Senoussi :

Rational design of controllable active matter 
Living systems have the incredible ability to organize themselves from molecules to the macroscopic scale. To understand the complex processes involved, we are reproducing some features of morphogenesis by rationally designing spatiotemporal patterns in artificial active materials.
Inspired by earlier works, we designed a minimal system composed of microtubules and multimers of kinesins that can convert chemical energy into large-scale mechanical work. We expressed, purified each molecular components and rationally assembled them. Depending of the initial concentrations, this in vitro system exhibits a rich diversity of structures, from a contractile network to an extensile active solution. Taking advantage of the predictable interactions between their sequences, we coupled this minimal system with DNA molecules. Upon the addition of a specific DNA strand, the system can undergo a macroscopic change resulting in a global contraction.
This approach can be used to create original out-of-equilibrium systems that link a DNA-based chemical reaction network capable of generating a concentration landscape with a force-generating system.