1. Pretransitional effects of the isotropic liquid-plastic crystal transitionAleksandra Drozd-Rzoska, Szymon Starzonek, Sylwester Rzoska, Joanna M. Łoś, Zdravko Kutnjak, Samo Kralj, 2021, izvirni znanstveni članek Opis: We report on strong pretransitional effects across the isotropic liquid–plastic crystal melting temperature in linear and nonlinear dielectric response. Studies were carried out for cyclooctanol (C8H16O) in the unprecedented range of temperatures 120 K < T < 345 K. Such pretransitional effects have not yet been reported in any plastic crystals. Results include the discovery of the experimental manifestation of the Mossotti Catastrophe behavior, so far considered only as a hypothetical paradox. The model interpretations of experimental findings are proposed. We compare the observed pretransitional behavior with the one observed in octyloxycyanobiphenyl (8OCB), typical liquid crystal (LC), displaying a reversed sequence of phase transitions in orientational and translational degrees of order on varying temperature. Furthermore, in its nematic phase, we demonstrate first-ever observed temperature-driven crossover between regions dominated by isotropic liquid and smectic A pretransitional fluctuations. We propose a pioneering minimal model describing plastic crystal phase behavior where we mimic derivation of classical Landau-de Gennes-Ginzburg modeling of Isotropic-Nematic-Smectic A LC phase behavior. Ključne besede: plastic crystal, melting, pretransitional behavior, nonlinear dielectric effect, dielectric constant, Mossotti Catastrophe Objavljeno v DKUM: 12.08.2024; Ogledov: 60; Prenosov: 8
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2. History-dependent phase transition characterJuš Polanšek, Arbresha Hölbl, Szymon Starzonek, Aleksandra Drozd-Rzoska, Sylwester Rzoska, Samo Kralj, 2022, izvirni znanstveni članek Opis: We consider history-dependent behavior in domain-type configurations in orientational order that are formed in configurations reached via continuous symmetry-breaking phase transitions. In equilibrium, these systems exhibit in absence of impurities a spatially homogeneous order. We focus on cases where domains are formed via (i) Kibble-Zurek mechanism in fast enough quenches or by (ii) Kibble mechanism in strongly supercooled phases. In both cases, domains could be arrested due to pinned topological defects that are formed at domain walls. In systems exhibiting polar or quadrupolar order, point and line defects (disclinations) dominate, respectively. In particular, the disclinations could form complex entangled structures and are more efficient in stabilizing domains. Domain patterns formed by fast quenches could be arrested by impurities imposing a strong enough random-field type disorder, as suggested by the Imry-Ma theorem. On the other hand, domains formed in supercooled systems could be also formed if large enough energy barriers arresting domains are established due to large enough systems’ stiffness. The resulting effective interactions in established domain-type patterns could be described by random matrices. The resulting eigenvectors reveal expected structural excitations formed in such structures. The most important role is commonly played by the random matrix largest eigenvector. Qualitatively different behavior is expected if this eigenvector exhibits a localized or extended character. In the former case, one expects a gradual, non-critical-type transition into a glass-type structure. However, in the latter case, a critical-like phase behavior could be observed. Ključne besede: topological defects, domains, disorder Objavljeno v DKUM: 01.07.2024; Ogledov: 140; Prenosov: 6
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3. 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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