Sommaire:

Biology has been an important source of inspiration for physics in the past. One famous example is the Brownian motion of seeds that finally lead to the determination of Avogadro’s number. Another example is the discovery of the first virus, Tabacco Mosaic Virus, that lead the famous paper of Onsager on the isotropic-nematic phase transition, showing that colloidal rods form the most basic system to study the origin of self-assembled structures. In this talk I will first show what can be learned from the dynamical behavior of individual rods about the nature of the equilibrium self-assembly in structure with no ordering, only orientational ordering and 1-, 2- and 3-D positional ordering [1,2]. This is experimentally achieved by tracking rod-like fd viruses with video fluorescence microscopy. The viruses are ideal model systems since they are very slender, monodisperse and can be made with variable stiffness. Dynamic signatures for the different phase transitions are obtained, leading to a reconsideration of the nature of the transitions. Another interesting aspect of colloidal rods is that they are very susceptible to external fields. In shear flow the torque on the rod will cause alignment, while in confinement rods tend to align with the wall. Both effects can drive or frustrate structure formation. In the second part of the talk, I will give several examples of this interplay of rod dispersions with external fields and show pathways to a microscopic understanding of the observed phenomena. Here I will also include experiments on F-actin in shear flow. [1] M. P. Lettinga and E. Grelet. Self-Diffusion of Rodlike Viruses through Smectic Layers. Phy. Rev. Lett. 99, 197802, 2007. [2] S. Naderi E. Pouget, P. Ballesta, P. van der Schoot, M. . Lettinga, and E. Grelet. Fractional hoping-type motion in columnar mesophase of semi-flexible rod-like particles. Phys. Rev. Lett. 2013.

Pour plus d'informations, merci de contacter Stocco A.