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Three-dimensional liquid crystalline superstructures for photonics (** joint talk with I-CAMP)

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The Mathematics of Liquid Crystals

Liquid crystalline materials allow for formation of complex optical and photonic patterns the superstructures- within the bulk of the material or by adding colloidal inclusions. Memory [1], self-assembly [2], topology [3], and material flow [4] can serve as guiding and controlling mechanism of the structures, offering possible competitive advantages to be used in complex optics and photonics. Here, we present three dimensional colloidal and bulk liquid crystal superstructures, as recently achieved by numerical modelling and experiments. Central to the superstructures are complex conformations of topological defects, as they can bind, stabilise, or distort the structure. We show that 3D colloidal crystals can be assembled from elastic dipoles of spherical beads in nematic liquid crystals [5] or via inherently inhomogeneous order profiles in bulk and confined cholesteric blue phases [6]. Colloidal crystals are generalised to close-packed colloidal lattices, which we show can serve as natural templates for defect networks [7]. Finally, photonic bands are calculated for selected structures and possible defects in the structure are discussed [8].

[1] T. Araki, M. Buscaglia, T. Bellini, H. Tanaka, Nature Materials 10, 303 (2011). [2] P. Poulin, H. Stark, T. C. Lubensky, D. A. Weitz, Science 275, 1770 (1997). [3] U. Tkalec, M. Ravnik, S. Copar, S. Zumer I. Musevic, Science 333, 62 (2011). [4] A. Sengupta, U. Tkalec, M. Ravnik, J.M. Yeomans, C. Bahr, S. Herminghaus, Phys. Rev. Lett. 110, 048303 (2013). [5] A. Nych, U. Ognysta, M. karabot, M. Ravnik, S. umer, I. Muevič, Nature Comm. 4, 1489 (2013). [6] M. Ravnik, G. P. Alexander, J. M. Yeomans, S. Zumer, Proc. Natl. Acad. Sci. USA 108 , 5188 (2011). [7] S. Copar, N.A. Clark, M. Ravnik, S. Zumer, Elementary building blocks of densely packed 3D colloidal lattice entangled by nematic disclinations, accepted in Soft Matter. [8] M. Stimulak and M. Ravnik, Photonic bands in blue phase colloidal crystals, to be submitted;

This talk is part of the Isaac Newton Institute Seminar Series series.

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