Critical behavior of dielectric permittivity in the isotropic phase of nematogens
About: This article is published in Physical Review E.The article was published on 1996-12-01. It has received 81 citations till now. The article focuses on the topics: Relative permittivity & Permittivity.
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TL;DR: A comprehensive overview of phase transition studies can be found in this article, where the authors identify the essential key concepts and points of difficulty associated with the study of phase transitions and discuss the most widely used experimental techniques for measuring these transition properties.
308 citations
TL;DR: In this article, the authors present experimental and theoretical results for the critical behavior in the isotropic phase of nematogens and discuss the possibility of tricritical behavior at the nematic-isotropic transition.
Abstract: The low value of , where is the nematic-isotropic phase transition temperature and denotes the virtual transition temperature, is a long-standing puzzle in the physics of liquid crystals. The present review presents experimental and theoretical results on this long-standing problem. New experimental and theoretical results for the critical behaviour in the isotropic phase of nematogens are reviewed. We calculate in a unified approach the low value of , at both critical and tricritical points. The possibility of tricritical behaviour at the nematic-isotropic transition is also discussed by means of Landau theory. The various predictions are compared with the available experimental results.
62 citations
TL;DR: Despite significant differences between N, Sm-A, and Sm-E phases the same pretransitional behavior of epsilon and NDE in the isotropic phase, described by critical exponents gamma = 1 and alpha = 0.5, was found.
Abstract: Results of studies of static dielectric permittivity (epsilon) and nonlinear dielectric effect (NDE) in the isotropic phase of 4-n-4'-isothiocyanatobiphenyl (nBT) homologous series from n = 2 to n = 10 exhibiting the isotropic-smectic E (I-SmE) transition, are presented. They are compared with results of similar studies in 4-cyano-4-n-alkylbiphenyls (nCB) from n = 4 to n = 12. In this homologous series isotropic-nematic (I-N) and isotropic-smectic-A (I-Sm-A) transitions take place. Despite significant differences between N, Sm-A, and Sm-E phases the same pretransitional behavior of epsilon and NDE in the isotropic phase, described by critical exponents gamma = 1 and alpha = 0.5, was found. It has been shown that when the length of the alkyl chain of a compound increases the discontinuity of the transition drops in nBT and rises in nCB. The influence of pressure on the discontinuity is also discussed.
62 citations
TL;DR: It is proved that both phase transitions are weakly first order, displaying a nearly tricritical behavior, and the width of metastable regions seems to be dependent on the physical magnitude, although specific heat and volumetric determinations allow for comparable results.
Abstract: Different kind of measurements were performed on the liquid crystal nonyloxycyanobiphenyl (9OCB) to carry out a study of the molecular dynamics in the smectic A (SmA), nematic (N), and isotropic (I) phases as well as an exhaustive analysis of both the SmA-to-N and N-to-I phase transitions. For the dynamic study, broadband dielectric spectroscopy (102 to 1.8 × 109 Hz) was used. Two orientations (parallel and perpendicular) of the molecular director with regard to the probing electric field were investigated. From this study, the static dielectric permittivity was obtained in both alignments and, in addition, the molecular motions that contribute to each one were discussed. The static dielectric data together with specific heat and volumetric determinations were analyzed, proving that both phase transitions are weakly first order, displaying a nearly tricritical behavior. However, the width of metastable regions seems to be dependent on the physical magnitude, although specific heat and volumetric determina...
41 citations
01 Jan 2007
TL;DR: In this article, the authors proposed a model for the TIP5P model of liquid transition and showed that the model can be used to study liquid-liquid miscibility in binary liquids under negative pressure.
Abstract: Part I: General Issues. Asteroid impact in the black sea a black scenario R.D.Schuiling et al.- The conductivity of hydrogen in extreme conditions V. T. Shvets et al.- Dynamic Crossover and liquid- liquid critical point in the TIP5P model of water P. Kumar et al.- Amorphization of ice by collapse under pressure, vibrational properties and ultraviscous water at 1 GPa G. P. Johari et al.- Coupled ordering in soft matter: competition of mesoscales and dynamics of coupled fluctuations M.A.Anisimov.- All standard theories and models of glass transition appear to be inadequate: missing some essential physics K L. Ngai.-Part II: Glass forming liquids. Positron annihilation lifetime spectroscopy and atomistic modeling - effective tools for the disordered condensed systems characterization J, Bartos et al.- Segmental and chain dynamics in Polymers C. M Roland and R. Casalini.-Isobaric and Isochoric properties of glass-formers R. Casalini and C. MRoland.-Molecular structure and relaxation processes in diisooctyl phthalate and diisooctyl maleate S. Pawlus et al.- Orientationally disordered glassy phases J. Ll.. Tamarit et al.- Part III: Liquid Crystals.Glassy dynamics ofrod - like liquid crystals: the influence of molecular structure A. Drozd-Rzosk et al.- Ordering effects on dynamics in glassforming mixture ofliquid crystals M Mierzwa et al.- Nonlinear dielectric spectroscopy near SmA - SmC* transition in ferrolectic liquid crystal DOBAMBC S. J. Rzoska and A. Drozd-Rzoska.-Confined liquid crystaline 5CB - combined temperature and high pressures dielectric relaxation studies S. Pawlus et al.-Annihilation of defects in liquid crystals M Svetec et al.-Waves at the nematic-isotropic interface: nematic-non-nematic and polymer-nematic mixtures V. Popa-Nita, T. J. Siuckin.- Part IV: Critical Liquids. Global phase behaviour of supercritical water - environmentally significant organic chemicals mixtures S. V. Artemenko and V. A.. Mazur.- Properties ofwater near its critical point V. Kulinskii, and N. Maiomuzh.-Fluctuational equation of state and slopes of critical curves near the critical point of solvent V. Rogankov and 0. Byutner.-Combined models of thermophysical properties along the coexistence curve E. E. Uszjuzhanin et al.-Intermolecular potential for simple liquids and gases in the high pressure region V. Yu.Bardic et al.-Homogeneous nucleation and growth from highly supersaturated vapor by molecular dynamics simulation N Lummen et al.-How to generate and measure negative pressure in liquids? A. R. Imre.- Indirect methods to study liquid-liquid miscibility in binary liquids under negative pressure A. R. Imre et al.-Part V: Bio-liquids and related problems. Critical properties of soft matter at restricted geometry as emerging problem: fundamentals and biological applications A. V. Chalyi et al.-Water-biomolecule systems under extreme conditions: From confinement to pressure effects M-C. Bellissent-Funel.- Recent progresses in understanding of water interacting with biomolecules, and inside living cells and tissues R. C. Ford and J. Li.- Self-assembly of polypeptides. The effect of thermodynamic confinement G. Floudas and P. Papadopoulos.-Coulomb liquids under electric field - application of a new computer simulation method E. S. Yakub.- Solvation effect in near-critical polar liquids A. Onuki.-
39 citations
References
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TL;DR: In this paper, the authors describe a mittlere Innere Feld einer nematischen Molekülanordnung abgeleitet, and gezeigt, daß this Innere Field in einem gewissen Temperaturbereich einen nematicalhen Ordnungszustand bewirken muß and daß dieser ordnung sustand was with einer bestimmten Temperatur diskontinuierlich und unter Energieaufnahme in die isot
Abstract: Mit Beschränkung auf den Dipol-Dipol-Anteil der reinen Dispersionswechselwirkungen als dem für die Existenz einer kristallinflüssigen Phase vermutlich maßgebenden Teil der zwischenmolekularen Kräfte wird durch geeignete Mittelungen ein Ausdruck für das auf das Einzelmolekül wirkende mittlere Innere Feld einer nematischen Molekülanordnung abgeleitet. Es wird gezeigt, daß dieses Innere Feld in einem gewissen Temperaturbereich einen nematischen Ordnungszustand bewirken muß und daß dieser Ordnungszustand bei einer bestimmten Temperatur diskontinuierlich und unter Energieaufnahme in die isotrope Molekülanordnung übergehen muß. Die Theorie liefert also einen Umwandlungspunkt 1. Ordnung, wie er experimentell auch beobachtet wird. Die Umwandlungstemperatur wird im wesentlichen durch die Anisotropie der optischen Übergangsmomente der Moleküle bestimmt.
1,328 citations
TL;DR: In this article, the authors have observed a divergence of the magnetic birefringence, and a critical increase and slowing of the fluctuations in order in the isotropic phase of a nematic liquid crystal.
Abstract: We have observed a divergence of the magnetic birefringence, and a critical increase and slowing of the fluctuations in order in the isotropic phase of a nematic liquid crystal. Our results are quantitatively described by a mean-field model except for a critical region close to the ordering temperature where the fluctuations are so large that the meanfield approximation fails.
290 citations
TL;DR: In this paper, an adiabatic scanning calorimeter has been used to study the thermal behavior of the liquid-crystal octylcyanobiphenyl (8CB) in the temperature range between 10 and 50°C.
Abstract: An adiabatic scanning calorimeter has been used to study the thermal behavior of the liquid-crystal octylcyanobiphenyl (8CB) in the temperature range between 10 and 50\ifmmode^\circ\else\textdegree\fi{}C. The solid---to---smectic-$A$ ($\mathrm{KA}$), the smectic-$A$---to---nematic ($\mathrm{AN}$), as well as the nematic-to-isotropic (NI) phase transitions, which fall in this temperature range, have been investigated in great detail. From our measuring procedure the enthalpy behavior (including latent heats) as well as the heat capacity have been obtained. For the KA transition the latent heat was 25.7\ifmmode\pm\else\textpm\fi{}1.0 kJ/mol and for the NI transition it was 612\ifmmode\pm\else\textpm\fi{}5 J/mol. Within the resolution of our experiment we find that the $\mathrm{AN}$ transition is a continuous one. For the latent heat, if any, we arrive at an upper limit of 0.4 J/mol (or 1.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ J/g). The observed anomaly in the heat capacity for the $\mathrm{AN}$ transition is not consistent with a nearly logarithmic singularity as predicted by the $\mathrm{XY}$ model, instead we obtain a critical exponent $\ensuremath{\alpha}={\ensuremath{\alpha}}^{\ensuremath{'}}=0.31\ifmmode\pm\else\textpm\fi{}0.03$. This result is consistent with the anisotropic scaling relation ${\ensuremath{
u}}_{\ensuremath{\parallel}}+2{\ensuremath{
u}}_{\ensuremath{\perp}}=2\ensuremath{-}\ensuremath{\alpha}$. The pretransitional effects near the NI transition are in qualitative agreement with the hypothesis of quasitricritical behavior.
174 citations
TL;DR: In this paper, the optical and d.c. pulsed field Kerr effects have been used to study the pretransitional behaviour in the isotropic phase for the alkyl cyano-biphenyl homologues (CN φ.φ CnH2n+1) for n = 5-8.
Abstract: The optical and d.c. pulsed field Kerr Effects have been used to study the pretransitional behaviour in the isotropic phase for the alkyl cyano-biphenyl homologues (CN φ.φ CnH2n+1) for n = 5–8. From the dynamic and static measurements both the relaxation time (τ) and the Kerr Constant B have been found to be proportional to (T-T*)−1. These results are interpreted in terms of the Landau - de Gennes model and the characteristic parameters of this formalism have been given. The results are discussed in terms of the changing chemical structure.
164 citations
TL;DR: In this paper, the authors measured the optical Kerr effect and the intensity-dependent ellipse rotation in order to study the pretransitional behavior of field-induced molecular alignment in the isotropic nematic substances.
Abstract: We have measured the optical Kerr effect and the intensity-dependent ellipse rotation in order to study the pretransitional behavior of field-induced molecular alignment in the isotropic nematic substances $p$-methoxy-benzylidene $p\ensuremath{-}n$-butylaniline (MBBA) and $p$-ethoxy-benzylidene-$p$-butylaniline (EBBA). The results agree well with predictions of the Landau---de Gennes model. Both the order-parameter relaxation time and the steady-state field-induced birefringence show critical divergence towards the isotropic \ensuremath{\rightarrow} nematic transition with a ${(T\ensuremath{-}{T}^{*})}^{\ensuremath{-}1}$ temperature dependence. In the case of MBBA, our results are also consistent with the results from light scattering, but the method we use is perhaps more straightforward and accurate. The nonlinear refractive indices and other relevant parameters of the materials are derived from the experiment.
135 citations