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: An overview of gases and liquids adsorption in the materials of Institute Lavoisier (MIL)-101(Cr), MIL-53(Cr) and silica materials is given in this article.
Abstract: We propose here to give an overview of gases and liquids adsorption in the materials of Institute Lavoisier (MIL)-101(Cr), MIL-53(Cr) and silica materials. We present some recent results of systems...
6 citations
Cites background or methods from "Calorimetric study of octylcyanobip..."
...[23,103,104] It is ascribed to the effect of the unidirectional field induced by the confinement and the interaction with the surface, which couples to the nematic order parameter....
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...[104] from a model derived from the Landau–de Gennes theory....
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01 Jan 2011
TL;DR: In this article, a review of the role of order and frustration in liquid-crystalline polymer networks (elastomers) is presented, focusing on smectic elastomers with high resolution X-ray diffraction.
Abstract: Order and frustration play an important role in liquid-crystalline polymer networks (elastomers). The first part of this review is concerned with elastomers in the nematic state and starts with a discussion of nematic polymers, the properties of which are strongly determined by the anisotropy of the polymer backbone. Neutron scattering and X-ray measurements provide the basis for a description of their conformation and chain anisotropy. In nematic elastomers, the macroscopic shape is determined by the anisotropy of the polymer backbone in combination with the elastic response of elastomer network. The second part of the review concentrates on smectic liquid-crystalline systems that show quasi-long-range order of the smectic layers (positional correlations that decay algebraically). In smectic elastomers, the smectic layers cannot move easily across the crosslinking points where the polymer backbone is attached. Consequently, layer displacement fluctuations are suppressed, which effectively stabilizes the one-dimensional periodic layer structure and under certain circumstances can reinstate true long-range order. On the other hand, the crosslinks provide a random network of defects that could destroy the smectic order. Thus, in smectic elastomers there exist two opposing tendencies: the suppression of layer displacement fluctuations that enhances translational order, and the effect of random disorder that leads to a highly frustrated equilibrium state. These effects can be investigated with high-resolution X-ray diffraction and are discussed in some detail for smectic elastomers of different topology.
6 citations
TL;DR: In this paper, a phase transition analysis of porous polyethyleneterephthalate (PET) films filled with octyl-cyanobihenyl (8CB) liquid crystal (LC) is reported.
Abstract: Results of optical investigations of the isotropic-nematic and nematic-smectic A phase transitions in porous polyethyleneterephthalate (PET) films filled with octyl-cyanobihenyl (8CB) liquid crystal (LC) are reported. Samples of porous films of thickness 23 µm with normally oriented cylindrical pores of a radius R ranging from 10 nm to 1000 nm were prepared using the track-etched membrane technology. The dynamic light scattering method was used to probe the nematic orientational fluctuations of confined LC samples. The corresponding relaxation time τ was measured as a function of R and temperature T at slow enough cooling rates (0.3–0.6 K/h) to locate the phase transition temperatures. Changes in τ(T) dependencies relatively sensitivity fingerprint the LC phase transformations. Experimental results are analysed using the Landau-de Gennes-Ginzburg phenomenological approach.
5 citations
Cites background or methods from "Calorimetric study of octylcyanobip..."
...The temperature shifts of the phase transition temperatures induced by confinement are of the same order of magnitude as those obtained at calorimetric studies of 8CB-pore glass system.[16] An additional information from our measurements can be extracted from the dependences of the effective relaxation time t on the pore’s diameter d presented in Figure 4....
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...These experimental parameters are close to those used in the calorimetric investigations of phase transitions of 8CB confined to porous glass matrices reported in [16]....
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...In addition to the cylindrical radius R, important role might be also played by several material dependent lengths.[16] These are the nematic order parameter correlation length ξn D ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi L= @(2)f ....
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...The mesoscopic degree of local LC orientational and translational ordering is expressed in terms of the nematic tensor Q and the smectic complex order parameter c [16]:...
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...The I-N phase transition temperature fulfills the condition [16] t eff D 1C sn providing sn < 0:5: For sn 0:5 the discontinuous I-N transition is replaced by a gradual evolution of orientational ordering on varying T....
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09 Apr 2008
TL;DR: In this article, an experimental study of the influence of an external field and alignment upon a colloid of a liquid crystal (octylcyanobiphenyl denoted 8CB) and a silica gel of aerosil nano-particles was presented.
Abstract: This thesis presents an experimental study of the influence of an external field and alignment upon a colloid of a liquid crystal (octylcyanobiphenyl denoted 8CB) and a silica gel of aerosil nano-particles. The first techniques used was an ACcalorimetry (alternating current heating) and the systems under investigation were firstly put under the influence of a magnetic field at John Hopkins University in Baltimore by professor Leheny’s group. The experiments revealed changes in transition temperatures, nematic range and critical coefficient that could account for what we called a ”memory” of the above mentioned structures. The second technique, dielectric spectroscopy, was applied to the same very densities of mixtures mentioned in the first paragraph. The samples were applied in one procedure an increasingly higher alternating electric field. An overall increase of the capacitance of the sample was measured. The second experiment was to reproduce the application of the magnetic field from the AC-calorimetry experiment now with an electric field. In dielectric spectroscopy case, an increase in transition temperature after the application of the procedure was revealed.
5 citations
Cites background or methods from "Calorimetric study of octylcyanobip..."
...Accurate ac-calorimetric data are available for the liquid crystal 8CB in controlled porous glass [40], aerogel [46], random aerosil gel [7], and aligned aerosil gel of this work....
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...an extended ”single-pore” model to account for surface anchoring [40]....
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...Comparison of the derived LC+QRD energy density W 2/K̄ as a function of ρS for the 8CB+QRD (8CB+aerogel [46], 8CB+CPG [40], random 8CB+sil [7], and aligned 8CB+sil [this work])....
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...10 Comparison of the derived LC+QRD energy density W (2)/K̄ as a function of ρS for the 8CB+QRD (8CB+aerogel [46], 8CB+CPG [40], random 8CB+sil [7], and aligned 8CB+sil [this work])....
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TL;DR: In this paper, the authors show that embedding chromophores in an array of conical channels 13 nm across in monolithic silica results in mesoscopic anisotropic matter and thus in a hybrid material showing second-harmonic generation.
Abstract: Second-order nonlinear optics is the base for a large variety of devices aimed at the active manipulation of light. However, physical principles restrict its occurrence to non-centrosymmetric, anisotropic matter. This significantly limits the number of base materials exhibiting nonlinear optics. Here, we show that embedding chromophores in an array of conical channels 13 nm across in monolithic silica results in mesoscopic anisotropic matter and thus in a hybrid material showing second-harmonic generation. This nonlinear optics is compared to the one achieved in corona-poled polymer films containing the identical chromophores. It originates in the confinement-induced orientational order of the elongated guest molecules in the nanochannels. This leads to a non-centrosymmetric dipolar order and hence to a nonlinear light-matter interaction on the sub-wavelength, single-pore scale. Our study demonstrates that the advent of large-scale, self-organized nanoporosity in monolithic solids along with the confinement-controllable orientational order of chromophores at the single-pore scale provides a reliable and accessible tool to design materials with a nonlinear meta-optics.
5 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