Calorimetric study of octylcyanobiphenyl liquid crystal confined to a controlled-pore glass.
TL;DR: The heat-capacity response at the weakly first order I-N and continuous N-SmA phase transitions gradually approaches the tricritical-like and three-dimensional XY behavior, respectively.
Abstract: We present a calorimetric study of the phase behavior of octylcyanobiphenyl (8CB) liquid crystal confined to a controlled-pore glass (CPG). We used CPG matrices with characteristic void diameters ranging from 400 to 20 nm. In bulk we obtain weakly first-order isotropic to nematic (I-N) phase transition and nearly continuous character of the nematic to smectic-A (N-SmA) phase transition. In all CPG matrices the I-N transition remains weakly first order, while the N-SmA one becomes progressively suppressed with decreasing CPG pore radius. With decreased pore diameters both phase transition temperatures monotonously decrease following similar trends, but increasing the stability range of the N phase. The heat-capacity response at the weakly first order I-N and continuous N-SmA phase transitions gradually approaches the tricritical-like and three-dimensional XY behavior, respectively. The main observed features were explained using a bicomponent single pore type phenomenological model.
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TL;DR: In this paper, the deuteron NMR and small-angle X-ray scattering (SAXS) spectra were used to study the ordering and phase transition behavior of octylcyanobiphenyl (8CB) liquid crystal confined to a controlled-pore glass with nontreated and silanes-treated pore surfaces.
Abstract: We present results of the deuteron nuclear magnetic resonance (NMR) and small-angle X-ray scattering (SAXS) study of ordering and phase transition behavior of octylcyanobiphenyl (8CB) liquid crystal confined to a controlled-pore glass (CPG) with nontreated and silanes-treated pore surfaces. The deuteron NMR spectra allowed to determine the degree of nematic liquid crystal ordering and also provided an indirect information on the confined 8CB smectic ordering via its influence on the nematic ordering. For the smectic phase these data are supplemented with measurements of the temperature dependence of the first-order SAXS diffraction pattern. The NMR results indicate that the average nematic and smectic order parameters of 8CB in the nontreated CPG are only weakly perturbed by the confinement. The SAXS data further suggest that in confined 8CB for both nontreated and silane-treated CPG a domainlike pattern appears in accordance with the Imry-Ma theorem.
15 citations
TL;DR: In this paper, a dielectric spectroscopy, magnetic susceptibility and high resolution calorimetry have been carried out in the vicinity of the ferroelectric smectic C* phase of SCE9 liquid crystal mixtures with magnetic nanoparticles (NPs) to determine the impact of the NPs on the Goldstone and soft mode and to study the disordering effects on the Ferroelectric phase transition.
Abstract: A dielectric spectroscopy, magnetic susceptibility and high resolution calorimetry have been carried out in the vicinity of the ferroelectric smectic C* phase of SCE9 ferroelectric liquid crystal (LC) mixtures with magnetic nanoparticles (NPs) to determine the impact of the magnetic nanoparticles on the Goldstone and soft mode and to study the disordering effects on the ferroelectric phase transition. It was verified via SQUID susceptometer that the indirect coupling between the NPs magnetic moments and the LC electrical polarization exists in these mixtures.
15 citations
TL;DR: The orientational and translational order of a thermotropic ferroelectric liquid crystal imbibed in self-organized, parallel, cylindrical pores with radii of 10, 15, or 20 nm in anodic aluminium oxide monoliths (AAO) are explored by high-resolution linear and circular optical birefringence as well as neutron diffraction texture analysis.
Abstract: The orientational and translational order of a thermotropic ferroelectric liquid crystal (2MBOCBC) imbibed in self-organized, parallel, cylindrical pores with radii of 10, 15, or 20 nm in anodic aluminium oxide monoliths (AAO) are explored by high-resolution linear and circular optical birefringence as well as neutron diffraction texture analysis. The results are compared to experiments on the bulk system. The native oxidic pore walls do not provide a stable smectogen wall anchoring. By contrast, a polymeric wall grafting enforcing planar molecular anchoring results in a thermal-history independent formation of smectic C* helices and a reversible chevron-like layer buckling. An enhancement of the optical rotatory power by up to one order of magnitude of the confined compared to the bulk liquid crystal is traced to the pretransitional formation of helical structures at the smectic-A*-to-smectic-C* transformation. A linear electro-optical birefringence effect evidences collective fluctuations in the molecular tilt vector direction along the confined helical superstructures, i.e. the Goldstone phason excitations typical of the para-to-ferroelectric transition. Their relaxation frequencies increase with the square of the inverse pore radii as characteristic of plane-wave excitations and are two orders of magnitude larger than in the bulk, evidencing an exceptionally fast electro-optical functionality of the liquid-crystalline-AAO nanohybrids.
14 citations
TL;DR: In this work, uniaxial thermotropic LCs confined to nanosized cylindrical cavities are studied using isobaric parallel tempering Monte Carlo (MC) Monte Carlo simulations and it is found that the LC director tends to align strongly with the axis of thecylindrical cavity, which outweighs the self-organization of the LC to hexagonal in-plane order.
Abstract: Applications of liquid crystals (LCs) are based on controlling the orientational and translational order of the medium. One important way of control is via confinement. In this work, uniaxial thermotropic LCs confined to nanosized cylindrical cavities are studied using isobaric parallel tempering (PT) Monte Carlo (MC) simulations. The LCs are modeled using the Gay–Berne (4.4, 20.0, 1, 1) (GB) potential in long, smooth-walled cavities. The chosen particle–wall interaction favours homogeneous planar anchoring – the alignment of molecules along the wall. We report the results for the phase structure appropriate to three different cavity sizes as well as comparison to the results of bulk simulations. Ensemble averages for orientational and translational order parameters as well as their local behavior as a function of the distance to the cavity wall is calculated by reweighting results from all the simulated temperatures. We find that the LC director tends to align strongly with the axis of the cylindrical cavity. The orientational order is enhanced and translational order suppressed by the walls of the cavity. Hence, there are notable differences between the local order close to the wall and near the cylinder axis. The position-dependent distributions of the order parameters result in smooth phase transitions in their respective system-wide averages. Particularly, the nematic–isotropic (N–I) transition is replaced by a continuous nematic–paranematic (N–PN) transition. This is caused by the core region of the cavities becoming isotropic at high temperatures, whereas near the wall the LC retains nematic order. In contrast to previous NVT ensemble simulations, we find the effect of confinement on the smectic (Sm) layering to be weak. Also, Sm–N and N–PN transitions are found to be both sharper and residing at higher temperatures than in the constant-volume simulations. At temperatures where the bulk LC is a solid, we observe a wall-induced density wave in the confined systems, which outweighs the self-organization of the LC to hexagonal in-plane order.
14 citations
TL;DR: In this article, the effect of electric field on the paraelectric-to-ferroelectric phase transition has been studied by quasi-isothermal calorimetric measurements on the classical ferroelectric BaTiO3 (BTO) single crystal oriented in the [001] direction.
Abstract: The effect of electric field on the paraelectric-to-ferroelectric phase transition has been studied by quasi-isothermal calorimetric measurements on the classical ferroelectric BaTiO3 (BTO) single crystal oriented in the [001] direction. The isothermal response of BTO exhibits a hysteresis at the field induced phase transition, however on approaching the critical point the asymmetry of the transition vanishes. The experimentally determined E-T phase diagram also shows a weak effect of the applied electric field on transition temperature at lower fields, whereas at higher fields the effect of the field becomes stronger.
14 citations
References
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Book•
01 Feb 1974
TL;DR: In this paper, the authors define an order parameter statistical theories of the nematic order phenomonological description of the nematic-isotopic mixtures and describe the properties of these mixtures.
Abstract: Part 1 Liquid crystals - main types and properties: introduction - what is a liquid crystal? the building blocks nematics and cholesterics smectics columnar phases more on long-, quasi-long and short-range order remarkable features of liquid crystals. Part 2 Long- and short-range order in nematics: definition of an order parameter statistical theories of the nematic order phenomonological description of the nematic-isotopic mixtures. Part 3 Static distortion in a nematic single crystal: principles of the continuum theory magnetic field effects electric field effects in an insulating nematic fluctuations in the alignment hydrostatics of nematics. Part 4 Defects and textures in nematics: observations disclination lines point disclinations walls under magnetic fields umbilics surface disclinations. Part 5 Dynamical properties of nematics: the equations of "nematodynamics" experiments measuring the Leslie co-efficients convective instabilities under electric fields molecular motions. Part 6 Cholesterics: optical properties of an ideal helix agents influencing the pitch dynamical properties textures and defects in cholesterics. Part 7 Smectics: symmetry of the main smectic phases continuum description of smectics A and C remarks on phase and precritical phenomena.
9,683 citations
TL;DR: The superconducting phase transition is predicted to be weakly first order, because of effects of the intrinsic fluctuating magnetic field, according to a Wilson-Fisher $\ensuremath{\epsilon}$expansion analysis, as well as a generalized mean-field calculation appropriate to a type-I superconductor.
Abstract: The superconducting phase transition is predicted to be weakly first order, because of effects of the intrinsic fluctuating magnetic field, according to a Wilson-Fisher $\ensuremath{\epsilon}$-expansion analysis, as well as a generalized mean-field calculation appropriate to a type-I superconductor. Similar results hold for the phase transition from a smectic-$A$ to a nematic liquid crystal.
653 citations
29 Apr 1996
TL;DR: In this paper, the authors provide a current treatise of the subject matter and places it in the broader context of electrooptic applications, taking an interdisciplinary approach to the subject, combining basic principles of physics, chemistry, polymer science, materials science and engineering.
Abstract: Focusing on the applied and basic aspects of confined liquid crystals, this book provides a current treatise of the subject matter and places it in the broader context of electrooptic applications. The book takes an interdisciplinary approach to the subject, combining basic principles of physics, chemistry, polymer science, materials science and engineering. Key Features:
572 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: Experimental and theoretical studies of the effects of quenched disorder on one-dimensional crystal ordering in three dimensions show extended short-range correlations that exhibit universal structure and scaling, anomalous layer elasticity, and glassy dynamics.
Abstract: We present experimental and theoretical studies of the effects of quenched disorder on one-dimensional crystal ordering in three dimensions. This fragile smectic liquid crystal layering, the material with the simplest positional order, is also the most easily deformed periodic structure and is, therefore, profoundly affected by disorder, introduced here by confinement in silica aerogel. Theory and experiment combine to characterize this system to an extraordinary degree, their close accord producing a coherent picture: crystal ordering is lost, giving way to extended short-range correlations that exhibit universal structure and scaling, anomalous layer elasticity, and glassy dynamics.
161 citations