1. Dynamics and pretransitional effects in C60 fullerene nanoparticles and liquid crystalline dodecylcyanobiphenyl (12CB) hybrid systemSylwester Rzoska, Szymon Starzonek, Joanna M. Łoś, Aleksandra Drozd-Rzoska, Samo Kralj, 2020, original scientific article Abstract: The report shows the strong impact of fullerene C60 nanoparticles on phase transitions and complex dynamics of rod-like liquid crystal dodecylcyanobiphenyl (12CB), within the limit of small concentrations. Studies were carried out using broadband dielectric spectroscopy (BDS) via the analysis of temperature dependences of the dielectric constant, the maximum of the primary loss curve, and relaxation times. They revealed a strong impact of nanoparticles, leading to a ~20% change of dielectric constant even at x = 0.05% of C60 fullerene. The application of the derivative-based and distortion-sensitive analysis showed that pretransitional effects dominate in the isotropic liquid phase up to 65 K above the clearing temperature and in the whole Smectic A mesophase. The impact of nanoparticles on the pretransitional anomaly appearance is notable for the smectic–solid phase transition. The fragility-based analysis of relaxation times revealed the universal pattern of its temperature changes, associated with scaling via the “mixed” (“activated” and “critical”) relation. Phase behavior and dynamics of tested systems are discussed within the extended Landau–de Gennes–Ginzburg mesoscopic approach.
Keywords: nanoparticles, liquid crystals, soft materials, fullerenes, dielectric spectroscopy, phase transitions, dynamics
Published in DKUM: 10.03.2025; Views: 0; Downloads: 6
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2. Pretransitional effects of the isotropic liquid-plastic crystal transitionAleksandra Drozd-Rzoska, Szymon Starzonek, Sylwester Rzoska, Joanna M. Łoś, Zdravko Kutnjak, Samo Kralj, 2021, original scientific article Abstract: 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.
Keywords: plastic crystal, melting, pretransitional behavior, nonlinear dielectric effect, dielectric constant, Mossotti Catastrophe
Published in DKUM: 12.08.2024; Views: 60; Downloads: 8
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3. History-dependent phase transition characterJuš Polanšek, Arbresha Hölbl, Szymon Starzonek, Aleksandra Drozd-Rzoska, Sylwester Rzoska, Samo Kralj, 2022, original scientific article Abstract: 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.
Keywords: topological defects, domains, disorder
Published in DKUM: 01.07.2024; Views: 140; Downloads: 9
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