Sommaire:

We study the patterning of cholesteric liquid crystal (CLC) alignment and the generation of defects via interfacial contact with Langmuir-Blodgett films exhibiting broken symmetries and interfacial topological defects. The films are previously self-assembled at the air/water interface where they organize into isolated sub-millimeter circular islands featuring polar nematic order with the elongated molecules anchored at a fixed angle of the interface normal (~ 45º), and a tilt orientation tangential to the circular boundary[1]. In contact with the LB-coated glass substrate, LC molecules follow the local in-plane orientation of the amphiphilic molecules in the monolayer. Previous work with nematic liquid crystals revealed the formation of either single twist-escaped or double singular arch-shaped defect loops, which were confined to the vicinity of the LB-coated plate, and were independent on the far-field boundary conditions [2]. When filling the cell with a CLC, the local twist imposed by the hybrid boundary conditions couples to the intrinsic cholesteric pitch, resulting in the formation of edge dislocations pinned between screw dislocations and kinks. Different three-dimensional imaging techniques (Fluorescence Confocal Polarizing Microscopy, and 2- and 3-photon fluorescent imaging) are employed to reveal the configuration of the director field. [1] J. Ignés-Mullol, J. Claret, R. Albalat, J. Crusats, R. Reigada, M. T. M. Romero and F. Sagués, Texture changes inside Smectic-C droplets in azobenzene Langmuir monolayers, Langmuir, 21, 2948 (2005). [2] N. Petit-Garrido, R. P. Trivedi, J. Ignés-Mullol, J. Claret, C. Lapointe, F. Sagués and I. I. Smalyukh, Healing of Defects at the Interface of Nematic Liquid Crystals and Structured Langmuir-Blodgett Monolayers, Phys. Rev. Lett., 107, 177801 (2011)

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