Effect of the network on the director fluctuations in a nematic side-group elastomer analysed by static and dynamic light scattering

The European Physical Journal E - Static and dynamic light scattering experiments were performed on monodomains of a crosslinked nematic side-group polysiloxane. The depolarized scattering caused...     

Reflection Phenomena in Particle Sizing by static and dynamic light scattering

Using a monodisperse poly(methyl methacrylate) dispersion it was shown that light reflection at the sample cuvette walls may greatly influence the results of both static (SLS) and dynamic (DLS) light scattering experiments. Considering SLS, this reflection phenomenon mostly causes an overestimation of the scattered intensity at high scattering angles, which may give rise to the emergence of an additional, artificial peak in the lower region of the particle size distribution. On the other hand, the influence of reflection on DLS experiments was shown to be particularly important in the upper region of the particle size distribution. The experimentally observed phenomena were explained from basic principles of both particle sizing methods. Finally, it was shown that the disturbing effect of reflection could be avoided by modifying either the hardware or the software of the SLS and DLS techniques.     

Interference patterns of scattering light induced by orientational fluctuations in an electric-field-biased nematic liquid-crystal film

A new light-scattering phenomenon from a planar aligned nematic liquid-crystal film is observed and studied. This new phenomenon exhibits ring patterns in the orthogonal polarization. A simple model based on optical interference has been developed, and its predictions agree well with experimental observation.     

The effect of magnetic field and convective flow on nematic director fluctuations

The slow orientational fluctuations of the director in the nematic state of d-PAA have been studied by real-time neutron scattering. By analysis of the measured time series we have derived the Hurst exponentH as a function of the applied magnetic field and of the applied vertical temperature difference of the sample. For zero values of both parameters we foundH0.9, indicating a high degree of temporal correlation between orientational fluctuations. At increasing field or temperature gradientH approaches a value of 0.5, corresponding to zero temporal correlations.     

Influence of barrier effects at interfaces on dynamic scattering of light in a nematic liquid crystal

The intensity of light dynamic scattering by a nematic liquid crystal with negative dielectric anisotropy (ZhK-440) as a function of the constant electric field strength has been studied under different interfacial conditions. It has been shown that potential barriers that arise at the interfaces not only influence the scattering intensity, but may also radically change the form of the dependence; i.e., the curves of optical transmission in the direction of the incident beam may have a minimum under certain field strengths. At higher strengths, the cells become totally transparent again. This anomalous behavior of the transmission curve is associated with the fact that the conductivity of the cells drops below a critical value with growing field strength, as the resistance of the space charge region at the inversely biased junction of the extraction electrode rises. In addition, it has been shown that the high resistance of the cells at low voltages may be attributed not only to a low concentration of impurities in the liquid crystal, but also to a low emissivity of the injecting electrode and a weak electron affinity of the extraction electrode.     

High pressure stability of protein complexes studied by static and dynamic light scattering

The high pressure dissociation of hemocyanin prepared from the lobster Homarus americanus and casein micelles from cow milk were observed by in situ light scattering. The hemocyanin dodecamer dissociated via a hexamer into monomers in a two-step three-species reaction. The influence of ligands and the effector l-lactate on the dissociation behavior was investigated. While no effect by carbon monoxide after exchanging the ligand oxygen was observed, the addition of the effector l-lactate led to a decrease in the pressure stability. Due to a trimer intermediate which was found to be stabilized by l-lactate, the dissociation reaction in the presence of the effector was analyzed by a three-step four-species reaction. In the case of casein micelles, a two-step dissociation mechanism was found. The stabilizing interactions of casein micelles were identified and separated.     

Simulation of multiple light scattering in a bounded nematic

The multiple-scattering problem is formulated for a single-constant model of a nematic liquid crystal with allowance for the dependence on the orienting external magnetic field. Based on the Bethe-Salpeter equation, an original Monte Carlo procedure in a birefringent medium is developed with allowance for the long-range action of dielectric permittivity fluctuations and backward and forward scatterings are calculated. The dependence of multiple scattering in a nematic on the distance between the incident and scattered rays is quantitatively studied for the first time and a nonmonotonic dependence on the external magnetic field is discovered. We numerically have established that the light-diffusion anisotropy noticeably weakens as compared to the extinction length anisotropy; this is shown to be caused by the weak anisotropy of the transport length.     

On the static and dynamic behaviour in nematic liquid crystals

Effective static exponents are calculated in the de Gennes model for isotropic-to-nematic phase transition. Applying parquet approximation we show that there are no stable fixed points for s?4. The dynamic exponent is evaluated in d?6 dimensions with the linear response theory.     

Contribution of the correlations of the director fluctuations to the neutron diffraction in the nematic phase

The intermolecular part of the nematic phase coherent neutron structure factor,S_inter(Q), including the correlations of the preferred molecular orientations, is calculated.     

Critical behaviour in solutions of branched polymers and swollen gels as studied by static and dynamic light scattering

Summary We present results of static and dynamic light scattering study of the critical phenomena in semi-dilute solutions and gels of poly(methyl methacrylate) (PMMA) prepared by radical copolymerization of methyl methacrylate and ethylene dimethacrylate in the θ-solvent (4-heptanone). The correlation length ξ and the extrapolated zero-angle scattering intensityI _c,0 of the solutions with degree of cross-linkingf _c≤1% diverge at the pseudospinodal temperature with exponents ofv=0.5 and γ=1, respectively, characteristic of mean-field behaviour. The values ofv and y for samples withf _c≥1.5% are about 0.6 and 1.2, respectively, indicating that the phase transition in solutions of branched PMMA molecules and PMMA gels can be classified to the 3D Ising model. The pseudospinodal temperaturesT _s, for semi-dilute solutions of branched molecules and gels were found as a function of the degree of cross-linking,f _c. The time autocorrelation functions consist of two contributions of which the faster one is attributed to the cooperative motions of the polymer matrix, while the broad slow mode is due to the dynamics of the partly penetrating polydisperse clusters and can be interpreted in terms of a simple cluster diffusion model. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Elastic scattering of light from quantum-well exciton-polarization fluctuations in a microcavity

A model of exciton polarization fluctuations in a quantum well of a randomly variable lateral width is proposed. The stochastic part of the nonlocal susceptibility of quasi-two-dimensional excitons is expressed through random functions of the shape of quantum well boundaries. A theory of elastic light scattering from a quantum well placed in a Fabry-Perot cavity or a semiconductor microcavity is constructed in the lowest (Born) approximation in interface roughness height. The scattering cross section is calculated for an arbitrary statistics of interface roughness. The spectral and angular dependences of the intensity of light scattered by a quantum well have been studied using Gaussian correlation functions of the interface shape. It follows from numerical estimates that elastic resonant scattering in quantum wells should be observed at an rms roughness height of the order of the atomic monolayer thickness.     

Effect of surface on phase modulation of light in a nematic layer

The nanorelief of orienting surfaces in a nematic layer is studied experimentally. The initial inclination angle of the director and the phase retardation of light in the crystal are determined, and the director reorientation dynamics in the crystal under SB deformation in an electric field is analyzed. It is shown that a thin layer of amorphous hydrogenated carbon (a-C: H) deposited on a GeO monoxide layer with an anisotropic nanorelief produced by the inclined deposition method smoothens the surface topography without changing the surface structure. Modification of the structure and physicochemical properties of the GeO surface alters the conditions of the anisotropic-elastic interaction at the interface with the liquid crystal, as evidenced by an increase in the S-effect threshold and a decrease in the initial inclination of the director from 22° (on the GeO surface) to 0–6°. Strong influence of the surface nanostructure on the dynamics of the director reorientation in the electric field and on the phase modulation of light is experimentally demonstrated. It is shown that the phase retardation of light in the GeO layer covered by an a-C: H film is twice as large as in the layer of the same thickness with a virgin surface.     

Dynamic fluctuations and static speckle in critical X-ray scattering from SrTiO3

We report a study of critical x-ray scattering from SrTiO3 near the antiferrodistortive structural phase transition at T(C) approximately 105 K. A line shape analysis of the thermal diffuse scattering results in the most precise experimental determination to date of the critical exponent gamma. The microscopic mechanism behind the anomalous "central peak" critical scattering component is clarified here by the first-ever observation of a static coherent diffraction pattern (speckle pattern) within the anomalous critical scattering of SrTiO3. This observation allows us to directly attribute the origins of the central peak to Bragg diffraction from remnant static disorder above T(C).     

Internal dynamics of a living cell nucleus investigated by dynamic light scattering

Recent progresses in cellular biology have shown that the nucleus of a living cell is a structured integration of many functional domains with a complex spatial organization. This organization, as well as molecular and biochemical processes, is time regulated. In the past years many investigations have been performed using fluorescent microscopy techniques to study the internal dynamics of the nucleus of a living cell. These investigations, however, have never focussed on the global internal dynamics of the nucleus, which is still unknown. In this article we present an original light scattering experimental device that we built to investigate this dynamics during biological processes. By means of this experimental set-up, we investigated the global dynamics of the nucleus of a living cell treated with a DNA replication inhibitor. This dynamics presents different and independent kinds of relaxation well separated in time that vary as a function of the cell cycle phases.     

光静态散射测试系统的研究与实现

随着科学技术的发展,对粒子的大小、浓度及其他特性的探测已经发展成为一个专门的研究领域和现代测量学中的一个重要分支,而光散射法已经成为一种常用的粒子测量方法。为了满足应用需求,文中提出了一种基于C8051F500单片机的光静态散射测试系统方案,详细介绍了该测试系统的设计理论原理、硬件电路的设计依据、固件程序的设计思想和测试系统的具体实现。选取一定浓度的样品溶液,运用该系统进行光散射的角度依赖性测试,实际测量值与理论依据基本相符;在不同激光功率下,对同一角度的散射光强进行测试,将测量得到的数据分析,线性度良好,满足设计要求。