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Accueil > Evénements > Séminaires > Archives 2015 > Chirality under confineme
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Chirality under confinement, multidimensional constraints in liquid crystalline materials - Piotr Sleczkowski - Mardi 3 mars 2015 à 13 h 30

INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-12 - 4e étage, salle 426

Piotr Sleczkowski - Ancien doctorant (soutenance en 2014) en cotutelle entre l’INSP et le Biomolecular Nanotechnology Group, MESA+ Institute for Nanotechnology, University of Twente.

Abstract

Liquid crystals are special type of materials which retaining to some extent the order of molecular organization also gain the dynamic properties. One of the main issues in liquid crystals research and also in the area of nanoscience and nanotechnology are studies of the interfaces between two different materials. Such interfaces, including the organic/inorganic interfaces, are particularly important for the development of devices, like Light-Emitting Diodes or Photovoltaic cells, in which the active layer is composed of liquid crystal molecules. In the first part of the talk research which was aimed at the understanding of behavior of mesogenic molecules under the influence of a metallic substrate (i.e. 2D confinement) will be described. It has been shown, by combining experimental and theoretical methods that under the influence of the solid substrate, combination of intermolecular and interfacial interactions may lead to the appearance of chirality. In particular, for the case of a model H5T molecule the self-assembled monolayers have shown the appearance of both : point and organizational types of chirality, despite of the fact that neither the molecule nor the substrate was chiral. Another molecular system, C-12 - a triphenylene peripherally substituted with azobenzene moieties – was also evidenced to form self-assemblies bearing the chiral nature. In the case of C-12 it has been shown that the origin of the self-assembly comes from the intermolecular interactions between the azobenzene moieties of neighboring molecules, which are substrate-mediated. Thus, the Au(111) substrate was proven to selectively support the self-assembly of C-12 in hexagonally packed domains. The main subject of study in the second part was investigation of the influence of the 3D confinement on the chirality in the chiral systems composed of cholesteric liquid crystals. The results presented are devoted to both static description of the system and dynamic studies. Due to the photo-responsive character of a chiral dopant used we were able to modify the cholesteric pitch of the CLC mixture and thus map the expression of chirality for varying geometrical confinement parameter : radius-to-cholesteric pitch. We evidenced a successful control of the cholesteric droplets by UV irradiation and we studied the induced structural variations.