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: The phase transition behaviour of various nematic side-chain liquid-crystalline elastomers with different mesogen composition is explored by means of high-resolution ac calorimetry and shows a strong dependence of the phase transition features upon the composition of the mesogen.
Abstract: The phase transition behaviour of various nematic side-chain liquid-crystalline elastomers with different mesogen composition has been explored by means of high-resolution ac calorimetry. Polydomain samples of the same crosslinking density and different type of mesogens have been investigated. The results show a strong dependence of the phase transition features upon the composition of the mesogen. The distance from the critical point, reflected in the sharpness of the heat capacity anomalies, increases when adding a shorter-length mesogen. The results provide new insight for the impact of mesogens on the thermodynamic behaviour and, thus, on the thermomechanical response of nematic liquid-crystalline elastomers.
1 citations
TL;DR: In this paper, the authors modify the Maier-Saupe mean field theory to include the disordering effects of porosity as a disordering surface potential and calculate the values of the nematic order parameter and hence find the TNI for different pore diameters.
Abstract: Experimental observations show that the N–I transition temperature (TNI) for liquid crystals embedded in solid porous materials is lower compared to that of the bulk liquid crystals and TNI is reduced linearly with the inverse pore diameter. To explain this, various theoretical studies have been proposed. We propose to use the mean field approach. We modify the Maier–Saupe mean field theory to include the disordering effects of porosity as a disordering surface potential. A molecule near the surface is assumed to feel the mean field potential (the Maier–Saupe type) and also the surface induced potential. We calculate the values of the nematic order parameter and hence find the TNI for different pore diameters. The weighted average of the order parameter is calculated considering the cylindrical symmetry of the pores. Our calculations on the variation of TNI with pore diameter agree with experimental data. Also, the calculated values of specific heat peak decrease with decrease in pore radius, in agreement with experimental trends.
1 citations
TL;DR: In this article, the influence of the electric field on a dielectric constant was studied by using PMN 1 − x PT x single crystal with x = 0.295, and it was shown that the complex dielectral constant exhibits significant dependence on the bias electric field in the vicinity of the liquid-vapor type critical point.
Abstract: The influence of the electric field on a dielectric constant was studied by the dielectric spectroscopy in PMN 1 − x PT x single crystal with x = 0.295. It is shown that the complex dielectric constant exhibits significant dependence on the bias electric field in the vicinity of the liquid-vapor type critical point. With increasing field and on approaching the critical point the dielectric constant exhibits enhancement and after crossing the critical field value both dielectric constant and loss factor decrease significantly. These results show that the proximity of the critical point may also play an important role in engineering of the electric-field tunable microwave elements.
1 citations
09 Jul 2012
TL;DR: In this article, the existence of indirect magnetoelectricity in a soft composite material prepared as a mixture of a ferroelectric liquid crystal (FLC) and magnetic nanoparticles (MNPs) was verified.
Abstract: By using the SQUID susceptometer the existence of an indirect magnetoelectricity in a soft composite material prepared as a mixture of a ferroelectric liquid crystal (FLC) and magnetic nanoparticles (MNPs) was verified. It is shown that the orientation of MNPs is directly coupled to the FLC molecular director field. Such coupling allows the possibility of indirect coupling between the MNP's magnetization and FLC's polarization. This demonstrates the possibility to engineer the soft magnetoelectrics from mixtures of magnetic nanoparticles and ferroelectric liquid crystals.
Cites background from "Calorimetric study of octylcyanobip..."
...And the LCs can also control the order in different nanometer and micro-sized building blocks [11, 12, 16, 20, 22]....
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...Intensive investigations show various aspects of interaction of nanoparticles (NPs) and the host LC [5-25]....
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01 Jan 2008
TL;DR: In this paper, the authors discuss some aspects and recent advancements of general measurement techniques that should benefit several characterization methods such as thermodynamic, magnetic, and transport studies of mesoscopic superconductors.
Abstract: Experimental research on mesoscopic systems puts high demands on the measurement infrastructure, including measurement system with associated sam- ple preparation, experimental design, measurement electronics, and data collection. Successful experiments require both the ability to manufacture small samples and to successfully and accurately study their novel properties. Here, we discuss some aspects and recent advancements of general measurement techniques that should benefit several characterization methods such as thermodynamic, magnetic, and transport studies of mesoscopic superconductors.
Cites background from "Calorimetric study of octylcyanobip..."
...When the liquid crystal becomes confined, it is known [16, 17] that the relative peak height changes and the transition temperature decreases, as is also seen in Fig....
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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