1. Experimental advances in nanoparticle-driven stabilization of liquid-crystalline blue phases and twist-grain boundary phasesGeorge Cordoyiannis, Marta Lavrič, Vasileios Tzitzios, Maja Trček, Ioannis Lelidis, George Nounesis, Samo Kralj, Jan Thoen, Zdravko Kutnjak, 2021, pregledni znanstveni članek Opis: Recent advances in experimental studies of nanoparticle-driven stabilization of chiral liquid-crystalline phases are highlighted. The stabilization is achieved via the nanoparticles’ assembly in the defect lattices of the soft liquid-crystalline hosts. This is of significant importance for understanding the interactions of nanoparticles with topological defects and for envisioned technological applications. We demonstrate that blue phases are stabilized and twist-grain boundary phases are induced by dispersing surface-functionalized CdSSe quantum dots, spherical Au nanoparticles, as well as MoS2 nanoplatelets and reduced-graphene oxide nanosheets in chiral liquid crystals. Phase diagrams are shown based on calorimetric and optical measurements. Our findings related to the role of the nanoparticle core composition, size, shape, and surface coating on the stabilization effect are presented, followed by an overview of and comparison with other related studies in the literature. Moreover, the key points of the underlying mechanisms are summarized and prospects in the field are briefly discussed.
Ključne besede: liquid crystals, nanoparticles, quantum dots, reduced-graphene oxide, calorimetry, microscopy, blue phases, twist-grain boundary phases, disclination lines, screw dislocations
Objavljeno v DKUM: 09.08.2024; Ogledov: 97; Prenosov: 9
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2. Smectic A herringbone patternsSamo Kralj, Emmanuelle Lacaze, George Cordoyiannis, Zdravko Kutnjak, 2014, objavljeni znanstveni prispevek na konferenci Opis: Two qualitatively different SmA structures exhibiting herringbone-type layer patterns, to which we refer as the Defectless Smectic Herringbone (DSH) and the Dislocation Decorated Smectic Herringbone (DDSH) pattern are studied by a Landau-de Gennes-Ginzburg mesoscopic approach. Liquid crystal structures are described in terms of a nematic director field and a smectic complex order parameter. It is demonstrated that, in the proximity of the N-SmA phase transition, a melting of smectic layers could be realised even for relatively weakly-tilted smectic layers in DSH patterns (i.e. θt ≈ 100) for type I Sm4 phase. The width of melted region could be relatively large with respect to bulk values of the smectic characteristic lengths. In addition, a critical value of θt is determined at which a DDSH pattern is expected to appear.
Ključne besede: liquid crystals, patterns, structural transitions
Objavljeno v DKUM: 30.06.2017; Ogledov: 2045; Prenosov: 386
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3. History-dependent patterns in randomly perturbed nematic liquid crystalsAmid Ranjkesh Siahkal, Milan Ambrožič, George Cordoyiannis, Zdravko Kutnjak, Samo Kralj, 2013, izvirni znanstveni članek Opis: We study the characteristics of nematic structures in a randomly perturbed nematic liquid crystal (LC) phase. We focus on the impact of the samples history on the universal behavior. The obtained results are of interest for every randomly perturbed system exhibiting a continuous symmetry-breaking phase transition. A semimicroscopic lattice simulation is used where the LC molecules are treated as cylindrically symmetric, rod-like objects interacting via a Lebwohl-Lasher (LL) interaction. Pure LC systems exhibit a first order phase transition into the orientationally ordered nematic phase at T = Tc on lowering the temperature T. The orientational ordering of LC molecules is perturbed by the quenched, randomly distributed rod-like impurities of concentration p. Their orientation is randomly distributed, and they are coupled with the LC molecules via an LL-type interaction. Only concentrations below the percolation threshold are considered. The key macroscopic characteristics of perturbed LC structures in the symmetry-broken nematic phase are analyzed for two qualitatively different histories at T << Tc. We demonstrate that, for a weak enough interaction among the LC molecules and impurities, qualitatively different history-dependent states could be obtained. These states could exhibit either short-range, quasi-long-range, or even long-range order.
Ključne besede: liquid crystals
Objavljeno v DKUM: 14.06.2017; Ogledov: 2300; Prenosov: 340
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4. Confined liquid crystaline 5CB in 2D thermodynamic space : preliminary dielectric relaxation studySebastian Pawlus, Jana Osinska, Sylwester J. Rzoska, Samo Kralj, George Cordoyiannis, 2007, objavljeni znanstveni prispevek na konferenci Opis: Results of preliminary broadband dielectric spectroscopy studies in a wide range of temperatures and pressures range for a mixture of rod-like liquid crystalline 4-cyano-4-pentylalkylbiphenyl (5CB) and hydrophilic silica spheres (Aerosil 300) are shown. Pretransitional anomaly, observed previously in the bulk 5CB, has been found. Temperature dynamics of the mixture was investigated with via the DC conductivity ?, coupled to the reorientational relaxation. The derivative based analysis of electric conductivity showed a clear non-Arrhenius dynamics and indicated the anomalous increase of the fragility strength coefficient on approaching the isotropic-nematic transition. Pressure investigations of the solidification from the nematic phase showed the increase of the transition temperature on pressuring but with unusual increasing of dTNS/dP coefficient.
Ključne besede: physics, liquid crystals, complex dynamics, random constraints, high pressures
Objavljeno v DKUM: 07.06.2012; Ogledov: 1634; Prenosov: 95
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