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 electric field stabilizes the phase or sequence of ferroelectric phases for materials close to morphotropic phase boundary and greatly reduces the thermal hysteresis effect.
Abstract: Thermal and electric field hysteresis effects near the ferroelectric transition were studied by a high resolution calorimetry and dielectric spectroscopy in several solid and soft disordered ferroelectrics such as perovskite relaxors and P(VDF-TrFE)-based ferroelectric polymers, respectively. Significant thermal hysteresis effects were observed in PMN-PT and SBN crystals as well as in P(VDF-TrFE) polymers reminiscent of the supercooling effect in glassy systems. Electric field effect on phase sequence and stabilization of hysteresis effects was also studied in PMN-PT, SBN, and P(VDF-TrFE) disordered ferroelectrics via dielectric and calorimetric experiments. It is shown that the electric field stabilizes the ferroelectric phase or sequence of ferroelectric phases for materials close to morphotropic phase boundary and greatly reduces the thermal hysteresis effect.
2 citations
20 Dec 2017
TL;DR: In this paper, a dynamic light scattering from the composite liquid crystal (LC) material, consisting of porous polyethylenterephthalate (PET) film filled with oсtylcyanobiphenyl (8CB), was obtained at the same time as simultaneous analysis of these parameters made possible to extract the temperatures TIN and TNA of the isotropic liquid- nematic (N-I) and nematic- smectic A (N -SmA) phase transitions in LC samples confined into cylindrical pores of diameters in the range of 0
Abstract: Autocorrelation function g2() and intensity (I) of the depolarized scattered light were obtained at the study of a dynamic light scattering from the composite liquid crystal (LC) material, consisting of porous polyethylenterephthalate (PET) film filled with oсtylcyanobiphenyl (8CB). The simultaneous analysis of these parameters made possible to extract the temperatures TIN and TNA of the isotropic liquid – nematic (N–I) and nematic – smectic A (N-SmA) phase transitions in LC samples confined into cylindrical pores of diameters in the range of 0.02 ... 2 μm. The dependences of TIN and TNA on the pore diameter were obtained and compared with the theoretical predictions. It was shown that simultaneous investigations of dynamic and static light scattering can be considered as a perspective approach for a study of phase transitions in LCs at strong confinement, which is typical for composite LC materials.
1 citations
Additional excerpts
...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 [12]....
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TL;DR: In this paper, two arms polarimetry is used for simultaneous measurements of the birefringence retardation and optical activity characterizing, respectively, orientational molecular ordering and chiral structuring inside nanochannels.
Abstract: We demonstrate an application of retardation-modulation polarimetry in studies of nanocomposite materials. Molecular ordering is explored on both nonchiral and chiral liquid crystals (LCs) in the bulk state and embedded into parallel-arrays of cylindrical channels of alumina or silica membranes of different channel sizes (12-42 nm). Two arms polarimetry serves for simultaneous measurements of the birefringence retardation and optical activity characterizing, respectively, orientational molecular ordering and chiral structuring inside nanochannels.
1 citations
TL;DR: The influence of the electric bias field on the SmA-SmC* phase transition in CE8 and BDH762 liquid crystals was studied by using dielectric spectroscopy and high-resolution calorimetry as mentioned in this paper.
Abstract: The influence of the electric bias field on the SmA-SmC* phase transition in CE8 and BDH762 liquid crystals was studied by using dielectric spectroscopy and high-resolution calorimetry. With increasing bias electric field the soft mode critical anomaly is increasingly suppressed and exhibits slight rounding effects. Similar smearing effects can be observed also in the heat capacity response. Well agreement with the standard model can be found in range of fields where the phase transition between the unwound C 1 and C 2 phases is expected.
1 citations
20 Aug 2015
TL;DR: Simulation of liquid crystals confined in both smooth and rough cylinders shows that QD reduces the order of orientation and translation, lessens the anisotropy of diffusion and shortens the rotational correlation time of the confined LCs with respect to the surface field.
Abstract: Quenched disorder (QD) and surface field are two key factors in nano-confinement researches. Despite decades of development, distinguishing the two factors is still challenging. To explore this issue, liquid crystals (LCs) confined in both smooth and rough cylinders are simulated and compared with the bulk LCs. The rough cylinders are aperiodical and produced firstly via randomly spherical indentation. Results show that QD reduces the order of orientation and translation, lessens the anisotropy of diffusion and shortens the rotational correlation time of the confined LCs with respect to the surface field. The intensity of the QD effects depends on the magnitude of the roughness of cylinders. In addition, the anisotropic diffusion of LCs exhibits a circular pattern when LCs system are cooled from the isotropic phase to the smectic phase. The simulated anisotropic diffusion validates the affine transformation model for the Bulk system in the isotropic and nematic phases. The model, however, underestimates the anisotropy of the confined systems. These results are helpful to develop physical models and explain experimental phenomena for confinement researches.
1 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