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Filamentous phages as chiral building blocks for hierarchical helical self-assembly.

THESIS IN PHYSICAL AND ENGINEERING SCIENCES, STARTING FALL 2019, BORDEAUX

The phase behavior of rod-shaped colloidal particles is much richer than that of their spherical counterparts in view of the additional orientational degrees of freedom that may drive so-called liquid crystal phases. The physics becomes even more complex when additional non-adsorbing polymers are present imparting so-called depletion interactions between the rods. In this PhD project, the candidate will perform experiments to study and understand the chirality transfer from the particle scale to the mesoscale through self-assembly of virus rods into a variety of chiral supramolecular morphologies (1D twisted ribbons, 2D hexagonal membranes, hexatic and bulk cholesteric phases,…). If chirality is ubiquitous in Nature from DNA to living organisms, the understanding of chirality amplification from chiral building blocks to ordered helical superstructures remains a challenge. Here, we will use a model system of chiral rod-like particles, namely the filamentous fd viruses which have unique physical properties, such as uniform particle lengths, rod helicity that can be tuned from left to right handed, that are not found in other model systems of rod-like colloidal particles. Rod-like viruses are also used as aqueous non-toxic cheap building blocks to create functional materials and biosensors. As colloids, they can be visualized and tracked at the single particle scale with optical microscopy. This enables a detailed and quantitative comparison with theoretical predictions and numerical simulations which has significantly advanced our understanding of soft matter physics in general and self-organization into liquid crystals.

Figure : Images of the different chiral morphologies to be studied in the PhD project (a) fd virus transmission electron microscopy image and schematic representation of its structure (b) Cholesteric phase of virus suspensions observed by polarizing microscopy (c) 1D twisted ribbon and (d) 2D hexagonal crystalline platelets (one presenting a screw dislocation) formed by fd condensation mediated by attractive depletion interaction and observed by DIC microscopy. The scale bars represent 50µm in (b) and 5µm in (c) and (d).  [1]

In this PhD Project, the candidate will study the formation of helical superstructures formed by attractive fd viruses, with a specific focus will be devoted to the role of topological defects in the mechanisms of chirality transfer at the mesoscopic scale, as well as to the influence of the geometric confinement in the resulting helical superstructures. The candidate will benefit from the strong collaboration with a theoretical group in Orsay.

PLEASE CONTACT (CV) :

- Eric Grelet
Centre de Recherche Paul Pascal (CRPP) UMR 5031
115 Av Schweitzer, 33600 Pessac, FRANCE ;
E-mail : Eric Grelet ; Tél : 05 56 84 56 13


[1] REFERENCES:B. Sung, A. de la Cotte, E. Grelet. Nature Communications 9, 1405 (2018). A. Repula, E. Grelet, Phys. Rev. Lett. 121, 097801 (2018). L. Alvarez, M.P. Lettinga, E. Grelet, Phys. Rev. Lett. 118, 178002 (2017). F. Tombolato, A. Ferrarini, E. Grelet, Phys. Rev. Lett. 96, 258302 (2006). E. Grelet , S. Fraden, Phys. Rev. Lett. 90, 198302 (2003).