New disclination networks ranging from rings to double helices found in confined blue phases are examined as trapping sites for the self-assemby of colloidal particles in complex 2D lattice structures. The Landau - de Gennes modelling combined with topology, that was proven to be useful in bulk blue phase colloids, is here used to study the dependence on confinement, particle properties, and the physical scale of the confined regions, ranging from micron to nanometre scale. Such quasi 2D colloidal crystals can be easily manipulated by external stimuli via affecting liquid crystal and/or colloidal particles are expected to yield novel photonic applications.
B.04 Guest lecture
COBISS.SI-ID: 2357604Recently, a revival of blue phase studies was stimulated by the discoveries of material mixtures of bimesogenic molecules that lead to BPs stable over a range of up to 50 K and polymer stabilized systems that allow applications. These phases of highly chiral liquid nematogenic molecules exhibit orientational order characterized by three-dimensional cubic lattices. The structures where a network of double-twist cylinders is intercalated by a network of -1/2 disclinations, is a result of the frustration occurring when space is filled with intrinsically preferred double twist configurations. We examine how blue phases I and II can be used as templates for colloidal crystals. Recent developments with extending the stability range make them more attractive for use in applications. Here we are particularly interested in effects of confinement when blue phases are constrained by the presence of colloidal particles or by the confinement to thin layers. 2D colloidal crystals can be tuned by external stimuli, like electric or magnetic field, or temperature. The effects on the liquid crystal and structure of colloidal particles is expected to have possible photonic applications.
B.04 Guest lecture
COBISS.SI-ID: 2345828Cholesteric blue phases (BPs) that can exist in complex fluids with internal orientational order in a temperature range between an isotropic and cholesteric phase are composed of a regular array of -1/2 disclinations and so-called double-twist cylinders. Here we present an investigation of BPs confined between parallel surfaces. With numerical calculations based on a Landau-de Gennes theory we show that the resulting structures strongly depend on the separation between confining surfaces, type & strength of surface anchoring, temperature, and chirality. Examples include arrays of: disclinations with double-helix form, disclination loops, undulating disclinations, and skyrmion structures. Structures are examined as 2D lattices of trapping sites that could stimulate self-assembling of particles. The phenomenological modelling combined with topology is used as a strong research tool to access intertwined effects of the physical scale of the confinement and the particle properties. Diverse photonic response is expected, to open new possible use in nano-optics and photonics.
B.04 Guest lecture
COBISS.SI-ID: 2359140