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 article, 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 (SHG).
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 (SHG) This non-linear optics is compared to the one achieved in corona-poled polymer films containing the identical chromophores It originates in confinement-induced orientational order of the elongated guest molecules in the nanochannels This leads to a non-centrosymmetric dipolar order and hence to a non-linear light-matter interaction on the sub-wavelength, single-pore scale Our study demonstrates that the advent of large-scale, self-organised nanoporosity in monolithic solids along with 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
TL;DR: In this paper, the influence of the bias field on the sequence of monoclinic phase transitions between the tetragonal and rhombohedral phases was studied by heat capacity measurements in PMN 1 − x PT x single crystal with x = 0.295.
Abstract: The influence of the electric bias field on the sequence of monoclinic phase transitions between the tetragonal and rhombohedral phases was studied by heat capacity measurements in PMN 1 − x PT x single crystal with x = 0.295. It is shown that besides the cubic to tetragonal (C-T) phase transition also tetragonal to monoclic C (T-M C ) phase transition exhibit a critical point at certain critical bias field value, thus terminating a line of first order transitions. It is shown by field cooled and zero-field cooled polarization experiments that similar critical point also exists in 9/65/35 PLZT ceramics.
5 citations
TL;DR: In this article, the temperature evolution of smectic ordering of 8CB liquid crystal confined to various CPG matrices was studied and substantial pretransitional anchoring was also observed, particularly in the silane-treated samples.
Abstract: We study the temperature evolution of smectic ordering of 8CB liquid crystal confined to various CPG matrices. The characteristic diameters of matrices ranged from 24 nm to 128 nm. The CPG voids were either left non-treated or were treated with silane. A weakly 1st order N-SmA transition in bulk 8CB, which could be attributed to the Halperin-Lubensky-Ma (HLM) effect, is broadened in confined samples. In confined samples substantial pretransitional anchoring was also observed, particularly in the silane-treated samples.
4 citations
TL;DR: A steady-state solution to the equation is presented such that the NI interface may propagate with a solitary-like wave profile under constant quenching, providing a plausible basis for the interpretation of the dynamical effects of quenched disorder in the liquid-crystal systems, caused by randomly interconnected porous media, such as aerosils.
Abstract: The effect of silica aerosils on the kinetics of the first-order nematic-isotropic (NI) phase transition is phenomenologically described in the framework of the time-dependent Landau-Ginzburg equation. A steady-state solution to the equation is presented such that the NI interface may propagate with a solitary-like wave profile under constant quenching. The results provide a plausible basis for the interpretation of the dynamical effects of quenched disorder in the liquid-crystal systems, caused by randomly interconnected porous media, such as aerosils. In the low silica aerosil ρs ( ≤0.1 g/cm^3) regime, the calculated values of the interface velocity v(T,ρs), the interface thickness κ(T,ρs), and the critical radius of a spherical nucleus of new nematic phase in a bulk isotropic environment, composed of polar molecules, such as 4-n-octyl- 4′- cyanobiphenyl and 4-n-heptyl- 4′- cyanobiphenyl shows that the effect of silica aerosils on the kinetics is reflected in a shifting of the set of temperature-dependent curves to lower temperature values.-1
4 citations
TL;DR: For the first time, a first-order nematic-isotropic phase transition was detected to take place inside such restrictive hosts as Merck Phase 4 and ZLI 1115 confined to mesoporous controlled pore glass materials.
Abstract: The behavior of thermotropic nematic liquid crystals (LCs) Merck Phase 4 and ZLI 1115 confined to mesoporous controlled pore glass materials was investigated using 13C nuclear magnetic resonance spectroscopy of probe molecules methyl iodide and methane. The average pore diameters of the materials varied from 81 to 375 A, and the temperature series measurements were performed on solid, nematic, and isotropic phases of bulk LCs. Chemical shift, intensity, and line shape of the resonance signals in the spectra contain lots of information about the effect of confinement on the state of the LCs. The line shape of the 13C resonances of the CH3I molecules in LCs confined into the pores was observed to be even more sensitive to the LC orientation distribution than, for example, that of 2H spectra of deuterated LCs or 129Xe spectra of dissolved xenon gas. The effect of the magnetic field on the orientation of LC molecules inside the pores was examined in four different magnetic fields varying from 4.70 to 11.74 T....
4 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