Rayleigh scattering induced by static bends of layers in a smectic A liquid crystal

We observe the anisotropy and the polarization properties of the Rayleigh scattered light for a planar smectic A texture of butoxyl benziledene-p-n anilino-acetophenone (BBAA). This scattering is attributed to static bends of the smectic layers, with wave vectors parallel to the smectic planes. This effect gives a simple method to measure the ratio of the extraordinary to the ordinary indices: n_e/n₀ = 1.18 at 89°C.     

Surface diffusion of matter in discotic liquid crystal threads

The first measurements of the surface diffusion coefficients in columnar discotic liquid crystal thread and film by an optical absorption technique are presented. A comparison of the results with the diffusion in the bulk specimen helps to introduce the number of diffusion sites in the surface and in the bulk. We propose then a structure of point defects in the mesophase. An estimation of jump frequency is deduced. The dependence of the surface diffusion versus the temperature seems in agreement with the Arrhenius law.     

Estimation of Rayleigh scattering loss in a double-clad photonic crystal fiber

In this paper the effect of photonic crystal fiber’s structure parameters on Rayleigh scattering was investigated. Rayleigh scattering loss (RSL) has been numerically estimated by average Rayleigh scattering coefficient based on the empirical relations for \(V\) and \(W\) parameters of double-clad photonic crystal fibers (DC PCFs). The dependence of RSL on the two structural parameters—the air hole diameter and the hole pitch was demonstrated. We have shown that RSL depends on the index profiles because of the different optical power confinement factors in every layer of DC PCF. Using these results, the RSL can be optimized by adjusting the fiber parameters—air-hole diameter as well as the air-hole pitch.     

The fine structure of depolarized Rayleigh scattering from liquid acetophenone

The depolarized Rayleigh spectrum I _H ^V of acetophenone exhibits a well-defined doublet structure. The form of this spectrum is analysed using recent microscopic theories (Keyes-Kivelson, Andersen-Pecora) and an older, viscoelastic theory (Rytov). At low temperatures a closer agreement is obtained with the theories of Keyes-Kivelson and Andersen-Pecora.     

The Rayleigh hypothesis in scattering off photonic crystal interfaces

We examine the Rayleigh hypothesis in the context of scattering of light off photonic crystal interfaces. First, the hypothesis - which was initially suggested for scattering of waves off rough surfaces between homogeneous media - is rephrased to apply to photonic crystal interfaces. Next, an exact and explicit functional form is presented that maps plane photonic crystal surfaces to periodic rough surfaces in free space, so that known criteria for the validity of the Rayleigh hypothesis for scattering at rough surfaces can be applied directly to scattering at the photonic crystal surfaces. The same map also allows the scattering problem to be solved exactly.     

Quasi-one dimensional electrical conductivity and thermoelectric power studies on a discotic liquid crystal

We have studied the electrical conductivity of well aligned samples of hexahexylthiotriphenylene (HHTT) in the pure as well as doped states. The dopant used was a small concentration (0.62 mole %) of the electron acceptor trinitrofluorenone (TNF). In the columnar phases, doping causes the AC(1 kHz) conductivity along the columnar axis (σ _‖) to increase by a factor of 10⁷ or more relative to that in undoped samples; σ _‖ attains a value of 10⁻²S/m, which was the maximum measurable limit of our experimental set up. On the other hand, in the isotropic phase doping makes hardly any difference to the conductivity. The frequency dependence of the conductivity has been investigated. The DC conductivity of doped samples exhibits an enormous anisotropy, σ _‖/σ _⊥ ≥ 10¹⁰, which is 7 orders higher than that reported for any liquid crystalline system, and, to our knowledge, the largest observed in an organic conductor. We also report the first thermoelectric power studies on these ‘molecular wires’. The sign of the thermoelectric power is in conformity with the expected nature of the charge carriers, namely, holes.     

Study of depolarized Rayleigh scattering in liquid benzene derivatives

The spectrum of the depolarized Rayleigh line has been measured for benzene, toluene, fluorobenzene and bromobenzene (at 22°c). The central part of the spectrum was measured at high resolution using a piezoelectric scanned Fabry-Pérot with a maximum free-spectral range of about 20 cm^-1. The entire spectrum was also measured with a monochromator extending the region to 100 cm^-1. The results from the two techniques were combined in order to deduce the correct line shape from which we were able to determine two relaxation times τ1 and τ2.     

Orientational diffusivities measured by Rayleigh scattering in a lyotropic calamitic nematic () liquid crystal phase: the backflow problem revisited

Using a light-beating technique we have measured the damping time of thermal fluctuations of the nematic director for the so called cylindrical or calamitic nematic (N_C) phase of the lyotropic system K-laurate/decanol/. By varying the scattering angle in suitable geometries, we have been able to estimate the orientational diffusivities associated to the three pure deformations of splay, twist and bend. A former measurement made in the disk-like N_D phase of the same system yielded a large deviation between the splay and twist diffusivities. The effect was then attributed to induced flows, or backflow, which could be responsible for the reduction of the splay viscosity. In fact, this is the analogous effect, for disks, to the one recognized since long time ago arriving for rod-like molecules in a classical nematic, though in this case it is associated with bend deformations. The analogy comes about thanks to the interchange of the role played by disks and cylinders for, respectively, splay and bend fluctuations.The measurements reported here provide a new test on the applicability of the backflow model to a nematic system composed of micelles, that is, aggregates made of amphiphilic (surfactant) molecules, in its cylindrical-like variant, i.e. the N_C phase. In addition, the comparative study made here with the previous results existing in the literature for the N_D phase, allows us to conjecture on structural issues concerning lyotropic nematics. Received: 29 April 1998 / Revised: 19 August 1998 / Accepted: 31 August 1998     

Observation of undulations of layers in the smectic B and H phases of a liquid crystal

We have observed scattering of light by static undulations, and by the undulation instability of the layers, in the B and H smectic phases. This would indicate that the B and H phases are closer to a liquid crystal than to a “plastic crystal”.     

Rayleigh scattering of Mössbauer radiation on a myoglobin single crystal

The RSMR technique was used to determine the fraction of radiation which is scattered elastically and inelastically, respectively, into Bragg reflections of a metmyoglobin single crystal. From this measurement 〈x² _1c〉=0.027±0.008 A² has been determined which is due to long range correlated motions in analogy to acoustic and optic modes in solids.     

Fast and slow dynamics in a discotic liquid crystal with regions of columnar order and disorder

Aromatic disk-shaped molecules tend to self-organize into a herringbone packing where the disks are inclined at angles ±θ with respect to the axis of the column. In discotic liquid crystals this can introduce defects between stacks of limited length. In a C(3)-symmetric hexa-peri-hexabenzocoronene, solid-state NMR, x-ray scattering, and rheology identifies such a packing with θ=43° and stacks of about seven disks. Disordered regions containing defects fill the space in between the ordered stacks. Biaxial intra- and intercolumnar dynamics differing by eight decades are identified.     

Orientational dependence of the potential of mean force for a discotic liquid crystal near a substrate

In this work we calculate the potential of mean force for a discotic liquid crystal (DLC) confined in a slab geometry. We have set the reaction coordinate as the distance between a DLC test particle with a fixed orientation and a wall with face-on anchoring. Five different orientations of the DLC test particle are explored, which correspond to parallel and perpendicular orientations with regard to the anchoring promoted by the walls, and three intermediate orientations between the parallel and perpendicular configurations. The potential of mean force reflects the strong effect of the system's anisotropy: particles with the wrong orientation are energetically penalised whilst the particles with the correct orientation are favoured.     

Photo-excitation of space charge fields and reorientation of a nematic liquid crystal of discotic molecules

A new reorientation effect in nematic liquid crystals of discotic molecules, which occurs under the combined influence of DC-electrical and optical fields, has been observed and investigated for the first time. It is shown that an illumination with intensity as low as 10⁻³ W/cm² is sufficient for producing a strong photo-induced reorientation process which indicates a rather large nonlinear optical coefficient. The dependence of the photo-excitation on the applied voltage as well as on the intensity and the wavelength of the light wave was investigated. Furthermore, a first model, which explains the experimental observations resulting from photo-induced space charge fields and related field-induced reorientation of the discotic molecules, will be discussed.     

苯并菲衍生物盘状液晶分子的非线性光学与热力学性质

采用密度泛函理论在B3LYP/6-31G**理论水平,计算并研究苯丙炔（烯）酸酯苯并菲盘状液晶分子的偶极矩、非线性光学性质、电子光谱和热力学性质.结果显示,该分子表现出良好的非线性光学性质,其二阶和三阶非线性光学系数分别为10⁴和10⁶a.u.数量级.其最低能量跃迁吸收波长分别为460和474nm,对应π到π*的电子跃迁.在温度298.15 K时,苯丙炔酸酯和苯丙烯酸酯苯并菲衍生物分子的标准摩尔生成焓分别为-7317.06和-1052.68 kJ·mo1^-1,标准摩尔生成自由能分别为-6186.91和117.00 kJ·mol ^-1.     

苯并菲衍生物盘状液晶分子的非线性光学与热力学性质

采用密度泛函理论在B3LYP/6-31G**理论水平,计算并研究苯丙炔(烯)酸酯苯并菲盘状液晶分子的偶极矩、非线性光学性质、电子光谱和热力学性质。结果显示,该分子表现出良好的非线性光学性质,其二阶和三阶非线性光学系数分别为104和106 a.u.数量级。其最低能量跃迁吸收波长分别为460和474 nm,对应π到π*的电子跃迁。在温度298.15 K时,苯丙炔酸酯和苯丙烯酸酯苯并菲衍生物分子的标准摩尔生成焓分别为-7317.06和-1052.68 kJ.mol-1,标准摩尔生成自由能分别为-6186.91和117.00 kJ.mol-1。