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The report presents static, low-frequency, and dynamic dielectric properties in the isotropic liquid, nematic, and solid phases of MBBA and related nanocolloids with paraelectric BaTiO3 nanoparticles (spherical, d = 50 nm). MBBA (4-methoxybenzylidene-4′–butylaniline) is a liquid crystalline compound with a permanent dipole moment transverse to the long molecular axis. The distortions-sensitive analysis of the dielectric constant revealed its hidden pretransitional anomaly, strongly influenced by the addition of nanoparticles. The evolution of the dielectric constant in the nematic phase shows the split into two regions, with the crossover coinciding with the standard melting temperature. The 'universal' exponential-type behavior of the low-frequency contribution to the real part of the dielectric permittivity is found. The critical-like pretransitional behavior in the solid phase is also evidenced. This is explained by linking the Lipovsky model to the Mossotti catastrophe concept under quasi-negative pressure conditions. The explicit preference for the 'critical-like' evolution of the apparent activation enthalpy is worth stressing for dynamics. Finally, the long-range, 'critical-like' behavior of the dissipation factor (D = tgδ), covering the isotropic liquid and nematic phases, is shown. [ABSTRACT FROM AUTHOR]

The long-range supercritical changes of dielectric constant, resembling ones observed in the isotropic liquid phase of liquid crystalline compounds, are evidenced for linseed oil—although in the given case, the phenomenon is associated with the liquid–solid melting/freezing discontinuous phase transitions. This 'supercriticality' can be an additional factor supporting the unique pro-health properties of linseed oil. Broadband dielectric spectroscopy studies also revealed the 'glassy' changes of relaxation times, well portrayed by the 'activated and critical' equation recently introduced. In the solid phase, the premelting effect characteristic for the canonic melting/freezing discontinuous transition, i.e., without any pretransitional effect in the liquid phase, has been detected. It is interpreted within the grain model, and its parameterization is possible using the Lipovsky model and the 'reversed' Mossotti catastrophe concept. For the premelting effect in the solid state, the singular 'critical' temperature correlates with the bulk discontinuous melting and freezing temperatures. Consequently, the report shows that linseed oil, despite its 'natural and complex' origins, can be considered a unique model system for two fundamental problems: (i) pretransitional (supercritical) effects in the liquid state associated with a weakly discontinuous phase transition, and (ii) the premelting behavior in the solid side of the discontinuous melting/freezing discontinuous transition. [ABSTRACT FROM AUTHOR]

The report shows the temperature behavior of the real part of dielectric permittivity in the static (dielectric constant) and low-frequency (LF) domains in bulk samples of 11CB and its BaTiO3-based nanocolloids. The study covers the isotropic liquid (I), nematic (N), smectic A (SmA), and solid crystal (Cr) phases. For each phase, the dominance of pretransitional fluctuations, significantly moderated by nanoparticles, is shown. The authors consider separate focuses on the dielectric constant ε T evolution in the static domain, yielding mainly response from permanent dipole moment and its arrangement, and in the low-frequency (LF) domain Δ ε ′ f = ε ′ f - ε (where ε ′ f is for the real part of dielectric permittivity in the LF domain), which is associated solely with ionic-related polarization mechanisms. All of these led to new experimental evidence concerning I–N, N–SmA, and SmA–solid transitions, focusing on the strength and extent of pretransitional effects, critical exponents, and phase transitions discontinuities. The strong evidence for pretransitional effects near the SmA–Cr transition is notable, particularly regarding Δ ε ′ f , T . Studies are supplemented by the discussion of DC electric conductivity—a parameter also related to the LF domain. Finally, the validity of the relation ε ′ f = Af - 3 / 2 + ε (where f stands for frequency, and A is a constant parameter), often used for discussing dielectric spectra in LC compound and its nanocolloids in the LF domain, is examined. [ABSTRACT FROM AUTHOR]

Melting/freezing are canonical examples of discontinuous phase transitions, for which no pretransitional effects in the liquid phase are expected. For the solid phase, weak premelting effects are evidenced. This report shows long-range, critical-like, pretransitional effects in liquid thymol detected in electrooptic Kerr effect (EKE) studies. Notably is the negative sign of EKE pretransitional anomaly. Studies are supplemented by the high-resolution dielectric constant temperature-related scan, which revealed a weak premelting effect in the solid phase. Both EKE and dielectric constant show a 'crossover' change in the liquid phase, ca, 10 K above the freezing temperature. It can be recognized as the hallmark of the challenging liquid–liquid transition phenomenon. [ABSTRACT FROM AUTHOR]

The report presents experimental results, which can be considered as the reference for innovative generations of supercritical fluids (SCF), liquid–liquid (LL), and liquid (L) extraction technologies. They are related to implementations of Critical Phenomena Physics, for such applications not considered so far. For the gas–liquid critical point, the shift SuperCritical Fluids (SCF) ⇒ SubCritical Fluids, due to the additional exogenic impact of ultrasounds, is indicated. For LL technology, the possibility of increasing process effectiveness when operating near the critical consolute under pressure is indicated. Finally, the discovery of long-range precritical-type changes of dielectric constant in linseed oil, standing even 50 K above the melting temperature, is presented. It suggests that extraction processes linking 'SCF' and 'L' technologies features and exploring the natural carrier, such as linseed oil, are possible. The report recalls the fundamental base for extraction processes via Kirkwood and Noyes–Whitney relations and presents their implementations to 'critical conditions,' including pressure. [ABSTRACT FROM AUTHOR]

Results of dielectric constant (ε) studies in diethyl ether for the surrounding of the gas - liquid critical point, TC - 130 K < T < TC + 50 K, are presented. The analysis recalls the physics of critical phenomena for portraying ε (T) evolution along branches of the coexistence curve, along its diameter (d(T)) and in the supercritical domain for T > TC. For the ultrasound sonicated system, the split into coexisting phases disappeared and dielectric constant approximately followed the pattern of the diameter. This may indicate the possibility of the extension of the "supercritical technology" into the ultrasound "homogenized" subcritical domain: the "strength" and the range of the precritical effect of d(T) are ca. 10× larger than for ε (T > TC). [ABSTRACT FROM AUTHOR]

Nonlinear dielectric effect (NDE) describes changes of dielectric permittivity induced by a strong electric field in a liquid dielectric. The most classical finding related to this magnitude is the negative sign of NDE in liquid diethyl ether (DEE), recalled by Peter Debye in his Nobel Prize lecture. This article shows that the positive sign of NDE in DEE is also possible, in the supercritical domain. Moreover, NDE on approaching the gas-liquid critical point exhibits a unique critical effect described by the critical exponent ≈ 0.4 close to critical temperature (TC) and ψ ≈ 0.6 remote from TC. This can be linked to the emergence of the mean-field behavior in the immediate vicinity of TC, contrary to the typical pattern observed for critical phenomena. The multi-frequency mode of NDE measurements made it possible to estimate the evolution of lifetime of critical fluctuations. The new way of data analysis made it possible to describe the critical effect without a knowledge of the non-critical background contribution in prior. [ABSTRACT FROM AUTHOR]

The temperature evolution of the primary relaxation time in the isotropic phase of 4-cyano-4'-tetradecylbiphenyl (14CB) above the isotropic-smectic A (I-SmA) transition is discussed. Based on the enthalpy space and distortionsensitive analysis, the prevalence of the mode coupling theory (MCT) "critical" and "glassy" dynamics is shown. The obtained singular dependence is related to the MCT critical temperature located approximately 48 K below the clearing (I-SmA) temperature. However, a weak but detectable distortion in the immediate vicinity of the transition occurs. It is also shown that the value of the fragile strength coefficient DT is characteristic of a very fragile glassy liquid whereas the steepness index m is typical of a strong one. Both magnitudes anomalously change on approaching the I-SmA phase transition. The static permittivity shows the pretransitional effect linked to the temperature of the hypothetical continuous phase transition located approximately 10.2 K below the I-SmA transition. [ABSTRACT FROM AUTHOR]

This article presents evidence for the long-range previtreous changes of two static properties: the dielectric constant (ε) and its strong electric field related counterpart, the nonlinear dielectric effect (NDE). Important evidence is provided for the functional characterizations of ε(T) temperature changes by the 'Mossotti Catastrophe' formula, as well as for the NDE vs. T evolution by the relations resembling those developed for critical liquids. The analysis of the dynamic properties, based on the activation energy index, excluded the Vogel–Fulcher–Tammann (VFT) relation as a validated tool for portraying the evolution of the primary relaxation time. This result questions the commonly applied 'Stickel operator' routine as the most reliable tool for determining the dynamic crossover temperature. In particular, the strong electric field radically affects the distribution of the relaxation times, the form of the evolution of the primary relaxation time, and the fragility. The results obtained in this paper support the concept of a possible semi-continuous phase transition hidden below Tg. The studies were carried out in supercooled squalene, a material with an extremely low electric conductivity, a strongly elongated molecule, and which is vitally important for biology and medicine related issues. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Broadband dielectric spectroscopy. • High pressures. • Liquid crystal (LC) based nanocollod. • Compressed nematogenic liquid crystal (LC) and its nanocolloid. • Continuous isotropic – nematic (I-N) transition under pressure. Landau-de Gennes mean-field model predicts the discontinuous transition for the isotropic – nematic (I-N) transition, associated with uniaxial ordering and a quadrupolar order parameter in three dimensions. This report shows pressure-related dielectric studies for rod-like nematogenic pentylcyanobiphenyl (5CB) and its nanocolloids with BaTiO 3 nanoparticles. The scan of the dielectric constant revealed the near-continuous I-N phase transition in the compressed nanocolloid with a tiny amount of nanoparticles (x = 0.1%). For the nematic phase in 5CB and its x = 1% nanocolloid the enormous values of the dielectric constant and the bending–type, long-range pretransitional behavior were detected. The impact of prenematic fluctuations was also noted for the ionic-related contribution to dielectric permittivity in the isotropic liquid phase. For the high-frequency relaxation domain, this impact was tested for the primary relaxation time pressure evolution and the translational–orientational decoupling. [ABSTRACT FROM AUTHOR]

Results of broad-band dielectric spectroscopy studies in liquid crystal (pentylcyanobiphenyl, 5CB)-based nanocolloids are presented. They reveal the strong impact of BaTiO3 nanoparticles on dynamics and uniaxial ordering. Studies were carried out in an extreme range of temperatures (~150 K), including the supercooled nematic phase. For the latter, the unique "pretransitional" effect for dielectric constant on approaching solid state is reported. The distortion-sensitive analysis revealed super-Arrhenius dynamics but associated with critical-like behavior. In the isotropic phase, translational-orientational decoupling, unusual for the high temperature dynamic domain, was detected. It can be directly link to heterogeneities--prenematic fluctuations. The model linking the classical Landau-de Gennes approach with Imry-Ma arguments has been developed to discuss experimental results. [ABSTRACT FROM AUTHOR]