Time-resolved simultaneous polarized and depolarized light scattering system with high sensitivity to optical anisotropy: application to phase separation of an optically isotropic liquid mixture

Depolarized light scattering is widely used to probe the spatial correlation of optical anisotropy in crystals, liquid crystals, and viscoelastic materials under stress, and a powerful means to study a non-equilibrium pattern evolution process of such a system. To follow the temporal change in the diagonal and off-diagonal contributions of the dielectric tensor, it is highly desirable to measure two-dimensional (2D) polarized (HH: horizontally transmitted, horizontally received) and depolarized (VH: vertically transmitted, horizontally received) scattering patterns simultaneously in a time-resolved manner. We develop a light scattering system with a video-rate time resolution as well as very high sensitivity to optical anisotropy. To detect extremely weak VH scattering from a sample without suffering from residual birefringence of the optical system itself and leakage of strong HH scattering signals, we use an objective lens specially designed for polarizing microscopy and Glan-laser prisms, respectively. This system enables us to experimentally elucidate the origin of VH scattering: we use the ratio of the VH and HH scattering intensity as a fingerprint for whether a 2D VH scattering pattern is caused by (i) optical anisotropy (intrinsic birefringence) or merely by (ii) spatial inhomogeneity of optically isotropic materials. We verify the validity of this method for a process of phase separation in a binary mixture of isotropic liquids. The simultaneous HH and VH measurement allows us to directly estimate the ratio of VH and HH scattering intensity accurately. The careful comparison of this ratio with a simple theory unambiguously demonstrates that the 2D VH scattering pattern is caused by the scattering angle dependence of the diffraction efficiency of light with the two polarization directions. That is, the origin of VH scattering is due to geometrical effects of the inhomogeneous distribution of the refractive index and not due to optical birefringence, as it should be for the optically isotropic sample. This method using the ratio of VH and HH scattering intensity may be widely used for distinguishing the two types of origins for a VH scattering pattern in an unambiguous manner.     

Spatial dispersion in chiral liquid crystals. Effects of higher orders

Abstract

Spatial dispersion effects in chiral liquid crystals are reviewed. New spatial dispersion phenomena are observed in the vicinity of the Bragg reflection wavelength–an anomaly of the refractive index and an optical anisotropy of the cubic blue phases. These effects can be explained by taking into account the spatial dispersion correction of the dielectric tensor of the medium of higher orders in the ratio of the light wave vector to the structural wave vector of chiral phases.     

UV and visible light screening by individual sporopollenin exines derived from Lycopodium clavatum (club moss) and Ambrosia trifida (giant ragweed)

We have investigated the UV-visible light transmission of three types of micrometre-sized sporopollenin exine shells, two derived from Lycopodium clavatum (club moss) spores and one from Ambrosia trifida (giant ragweed) pollen. We have used spectrophotometer measurements of partial monolayers of exines and microscope absorbance imaging to derive the light transmission properties of individual exines. Measurements have been made for exines in air when light transmission losses are due to a combination of absorption, reflection and scattering processes and for exines dispersed in a liquid for which the refractive index (RI) is approximately equal to the RI of the exine such that reflection and scattering effects are negligible. Overall, it found that the light transmission of a single exine wall is approximately 50%. This value of the transmission is due mainly to light absorption, is similar for the three exines studied here and varies only slightly with light wavelength over the range 200-900 nm.     

光纤折射率传感用于壳聚糖脱乙酰度测定

建立了一种基于光纤折射率传感技术的壳聚糖脱乙酰度测定方法. 利用光纤折射率传感器监测酸碱滴定过程中溶液折射率的变化, 根据折射率变化转折点之间碱的用量来计算壳聚糖的脱乙酰度. 该方法测得的3种不同含量实际样品的脱乙酰度与氢核磁共振波谱(¹H NMR)方法测定结果相符, 验证了方法的可靠性. 该方法具有用量少、 结构简单、 准确、 重复性好和转折点明显等优点, 可应用于工业生产中壳聚糖脱乙酰度的测定.     

Transparent Polymer Opal Thin Films with Intense UV Structural Color

We report on shear-ordered polymer photonic crystals demonstrating intense structural color with a photonic bandgap at 270 nm. Our work examines this UV structural color, originating from a low refractive index contrast polymer composite system as a function of the viewing angle. We report extensive characterization of the angle-dependent nature of this color in the form of ‘scattering cones’, which showed strong reflectivity in the 275–315 nm range. The viewing range of the scattering was fully quantified for a number of planes and angles, and we additionally discuss the unique spectral anisotropy observed in these structures. Such films could serve as low-cost UV reflection coatings with applications in photovoltaics due to the fact of their non-photobleaching and robust mechanical behavior in addition to their favorable optical properties.     

可录型光盘(CD-R)中染料膜层的光谱性质和光学特性

本文利用光在多层膜介质中的传播模型,计算了可录型光盘（ＣＤ Ｒ）中染料媒体的光学特性．表明在适合于ＣＤ Ｒ光盘记录的７８０ｎｍ波长处,由于多层膜中光的干涉作用,样品反射率随薄膜的厚度变化发生振荡．振荡的幅度和周期依赖于染料薄膜的复数折射率（ｎ＋ｉｋ）．当记录介质层的复数折射率在２．１＋ｉ０．０２至２．８＋ｉ０．１２之间时,能够满足ＣＤ Ｒ光盘对染料介质的要求．通过对三种菁染料薄膜的光谱性质分析及光学参数的模拟计算,证实了该方法用于染料薄膜光学特性研究的合理性．并为选择适合于光记录的染料薄膜的厚度范围提供了简便的方法     

Features of molecular light scattering and structure of the chlorobenzene–o-dichlorobenzene solutions

Structural Chemistry - The total light scattering coefficient, degree of depolarization, refractive index, and density were measured in chlorobenzene–o-dichlorobenzene solutions. The...     

Synthesis and Characterization of Highly Oriented Sol-Gel (Pb, La) TiO3 Thin Film Optical Waveguides

The preparation and the optical characteristics of highly oriented PLT thin films are investigated. PLT films fabricated on MgO(100) and c-plane sapphire substrates have highly grown in (100) and (111) orientations, respectively. PLT films with high La content have a near cubic structure and weak anisotropy of refractive indices. The optical propagation losses of PLT films decrease as the La content of the films increases due to a complex interaction of surface roughness reduction and a reduction in the anisotropy refractive index. However, optical scattering in thicker sol-gel PLT thin film waveguides occurs by the internal scattering mechanism from the defects and the interfaces rather than by the surface scattering mechanism.     

Large-area periodic lead halide perovskite nanostructures for lenticular printing laser displays

Lenticular printing technique provides a promising way to realize stereoscopic displays,especially,when microscopic optical structures are integrated into light-emitting materials/devices.Here,we fabricated large-area periodic structures with a spatial resolution at a wavelength scale from hybrid perovskite materials via a space-confined solution growth method.It takes advantages of both high refractive index contrast and high luminescence brightness,which allows the optical modulation on not only the reflection of illumination,but also the light emission from hybrid perovskites.The distributed feedback within these periodic structures significantly improves the degree of polarization and directionality of laser actions while their threshold is also reduced.These findings enable us to present a prototype of lenticular printing laser displays that vary emission colors at different view angles,which may find applications in creating high-resolution and high-contrast holographical images.     

Iron-dextran complex: geometrical structure and magneto-optical features

Molecular mass of the iron-dextran complex (M(w)=1133 kDa), diameter of its particles (～8.3 nm) and the content of iron ions in the complex core (N(Fe)=6360) were determined by static light scattering, measurements of refractive index increment and the Cotton-Mouton effect in solution. The known number of iron ions permitted the calculation of the permanent magnetic dipole moment value to be μ(Fe)=3.17×10(-18) erg Oe(-1) and the determination of anisotropy of linear magneto-optical polarizabilities components as Δχ=9.2×10(-21) cm(3). Knowing both values and the value of the mean linear optical polarizability α=7.3×10(-20) cm(3), it was possible to show that the total measured CM effect was due to the reorientation of the permanent and the induced magnetic dipole moments of the complex. Analysis of the measured magneto-optical birefringence indicated very small optical anisotropy of linear optical polarizability components, κ(α), which suggested a homogeneous structure of particles of spherical symmetry.     

Quantitative analysis of infrared absorption coefficient of spider silk fibers

Spider silk has a high degree of crystallinity comprising nanocrystals which are interlinked by amorphous regions containing pre-strained spidroin chains. Both, crystal volume fraction and crystal size were shown to be critical for the macroscopic mechanical properties of silk. In this study, for the first time, quantitative results were obtained from absorption IR spectra. Two main difficulties must be overcome: the cylindrical sample geometry and the absence of suitable reference spectra. We show that it is possible to get reproducible absorption coefficient spectra from dense parallel fiber grids immersed in a refractive index matching liquid. Comparison with model polypeptides yields the nanocrystal volume fraction that is close to the crystallinity values given by solid-state NMR or X-ray scattering.     

A study of structure formation processes occurring with the gelation of polysulfonamide solution in dimethylacetamide

This work investigates spontaneous gelatination of polysulfonamide in the solution of dimethylacetamide by nuclear magnetic relaxation, small-angle light scattering, and refractive index measurement. Two stages of the gelatination process were found to occur. Spherulites are formed in the first stage while the mobility of the solvent molecules decreases sharply. The second stage is characterized mainly by perfection of the inside structure of spherulites without a change in their size. The degree of decreasing mobility of the solvent molecules is much less in this stage than in the first stage.     

Applications of index matching in reflectometry,SANS and Brewster angle microscopy

By index matching, we mean, the manipulation of the composition of a material such that heterogeneous regions of a sample present identical refractive indices. Such manipulation is commonly used to exaggerate deviations from bulk properties at the interface between two bulk phases. Whilst index matching is used routinely in small-angle scattering it is in the field of neutron reflection that the technique has only recently been exploited fully. Specific deuteration, either inter- or intramolecular combined with partial structure factor (PSF) analysis has allowed structural detail to be elucidated at resolutions of ∼4 Å. In light scattering Brewster angle microscopy exploits the extinction of ‘p’ polarised light to enhance surface inhomogeneites on the scale of microns.     

Small-Angle light scattering from an anisotropic sphere: Anisotropy and size effects

The recently developed theory of light scattering from an anisotropic sphere (taken as a model for a spherulite) summarizes all information obtainable from such scattering system when the Rayleigh-Gans-Debye approximation is appropriate. The commonly used procedure of size determination from the maximum of the H_v intensity is tested for a number of models differing in radius size, inherent anisotropy δn and mean refractive index ¯n. It has been confirmed, that the parameter (¯n - 1)/δn plays the decisive role in the angular dependence of the H_v intensity and the influence of that parameter on the size determination and resulting accuracy is specified. The results differ for positive and negative spherulites and the stabilizing role of increasing spherulite size in accuracy of procedure is demonstrated. It has been shown that the RGD approximation is appropriate especially for the case of homogeneous spherulite texture (thus implying, that the refractive index of the surrounding is close to the average refractive index of a single spherulite). The results extrapolated outside of the RGD approximation display invariable U_max position for isotropic contribution with increasing sphere size in contrast to the oscillatory character of U_max predicted by the LM solution. It is proposed to construct the anisotropic solution under an approximation recently suggested for thin anisotropic shell. © 1994 John Wiley & Sons, Inc.     

Degree of aggregation of indocyanine green in aqueous solutions determined by Mie scattering

Indocyanine green in water and aqueous NaCl solutions forms large J-aggregates. The degree of aggregation is estimated by Rayleigh scattering and Mie scattering analysis. The refractive index of the aggregates responsible for scattering is deduced from an aggregate absorption cross-section spectrum using the Kramers-Kronig relations. The average degree of aggregation for indocyanine green in water is found to be of the order of 10⁷ while it rises to 10⁹ for indocyanine green in 0.01 molar aqueous NaCl solution.     

Light scattering by cellulose. III. Morphology of wood

Radial, tangential and cross cuts of Eastern spruce are examined by a solid-state light-scattering method which allows study of light scattering due to fluctuations in density and fluctuations in anisotropy. All of the samples investigated show well-defined scattering maxima which are related to their anisotropic texture with limited contributions from random density fluctuations. The radial cuts give rise to scattering similar to that by a grating with orthogonal characteristic spacings. The gratinglike character is due mainly to the pit structure and their periodic spacings, which can be deduced from the “unit-cell” dimensions of the scattering pattern. The scattered intensity is maximum when the fiber direction is at 45° to the polarization direction; when it is either horizontal or vertical, a distinct “spherulitic” scattering is observed from which size and asymmetry of the pits can be deduced.     

Peculiarities of molecular light scattering in a chlorobenzene—<Emphasis Type="Italic">o</Emphasis>-dichlorobenzene system and their relationship to the solution structure

The general coefficient of molecular light scattering (R ₀), degree of depolarization (ΔU), and refractive index (n) in a system of o-dichlorobenzene—chlorobenzene solutions were measured. The anisotropic (R _a) and isotropic (R _is) contributions to scattering and the iso-thermal compressibility and its excess component were calculated. A complicated nonmono-tonic behavior was found for the concentration dependences of the coefficients of molecular light scattering with a minimum in a range of low concentrations from the side of chlorobenz-ene and a maximum from the side of o-dichlorobenzene, indicating a substantial rearrange-ment of the structure of the solutions with a change in the concentration. An analysis of the concentration dependences of the coefficients of molecular light scattering, excess isother-mal compressibility, and excess molar volume revealed four ranges differed in structure: 0—0.03, 0.03—0.65, 0.65—0.9, and 0.9—1.0. The solution structure was described in each range.     

Water-soluble, self-assembling container molecules: an update

Over the past five years, an important development in the area of self-assembling containers has been the increase in interest in those containers that function in aqueous solution. This progress is a reflection of a similar trend within supramolecular chemistry in general, and is driven in part by the need to address issues and challenges within the biological sciences, as well as a desire to develop new strategies for greener chemistries carried out in water. It is also an opportunity to learn more about fundamental topics such as the hydrophobic effect. In this critical review we discuss progress in aqueous-based self-assembling container molecules since 2005 (177 references).     

Dependence of chain conformation and solution thermodynamics on composition for poly(ortho ester)s prepared from ketene acetals and mixtures of diols

The solution properties of a series of random copolymers prepared from ketene acetals with mixtures of diols have been characterized by dilute solution light scattering, chromatographic, and viscometric techniques. Five solvents with refractive indices ranging from 1.4 to 1.5 were used to obtain the correct weight average molecular weight. Changes in the unperturbed radius of gyration, obtained by combined size exclusion chromatography and low-angle light scattering techniques, parallelled that predicted by simple considerations of changes in repeat unit size. Thus the relative contributions of differing copolymer–solvent interactions and changing unperturbed radii of gyration to the hydrodynamic volume of random copolymers of different compositions were evaluated.