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Topological defects in anisotropic soft materials - Samo Kralj - endredi 28 juin 2013 à 10 h 30

Samo Kralj, Faculty of Natural Sciences and Mathematics, University of Maribor and Jozef Stefan Institute, Ljubljana, Slovenia
Vendredi 28 juin 2013 à 10 h 30 - Salle 406, couloir 22-12 - 4e étage

Topological defects (TDs) are unavoidable consequence of continuous symmetry breaking phase transitions. They exhibit several universal features and often span apparently completely different systems. Particularly convenient testing ground to study basic physics of TDs are liquid crystals (LCs) due to their softness, liquid character and optical anisotropy. In the lecture I will present our recent theoretical studies of TDs in nematic LCs, which are of interest also to other branches of physics.

I will first focus on coarsening dynamics of TDs following the isotropic-nematic phase transition. Among others we have tested the validity of the Kibble-Zurek [1,2] prediction on the size of the so called protodomains, which was originally derived to estimate density of TDs as a function of inflation time in the early universe. Next I will consider nematic LC shells [3]. These systems are of interest because they could pave path to mm sized scaled crystals exhibiting different symmetries. Particular attention will be paid to curvature induced unbinding of pairs of topological defects. This process might play important role in membrane fission processes. Finally, I will demonstrate how appropriate nanoparticles (NPs) could be exploited to stabilize various defect lattices in chiral LCs [4]. Shown examples have several analogues in other condensed matter systems. For example, NP-driven stabilization of smectic twist grain boundary phase is analogous to impurity stabilized Abrikosov phase in type II superconductors.

[1] W.H. Zurek, Nature 317, 505 (1985).
[2] Z. Bradac et al., J.Chem.Phys 135, 024506 (2011).
[3] S. Kralj et al., Soft Matter 7, 670 (2011) ; 8, 2460 (2012).
[4] G. Cordoyiannis et al., Soft Matter 9, 3956 (2013).