Light-scattering Patterns Research Articles

Electrolysis inducespHgradients and domain orientation in agarose gels

We have used small-angle light-scattering (SALS), microscopy, and measurements to study structural changes produced in unbuffered agarose gels as ions migrate under applied electric fields (3-20 V/cm). Anisotropic, bowtielike, light-scattering patterns were observed, whose development occurred more quickly at higher fields. The horizontal lobes were more pronounced at higher polymer concentration. Analysis of the SALS data with a simple model of scattering from anisotropic rods in an electric field is consistent with anisotropic rodlike domains on the order of 10-15 microm in length, which align perpendicular to the electric field. The anisotropic domains in the gel reach almost the same level of orientation, regardless of the field strength. Microscope imaging revealed anisotropic domains on the same length scale, also aligned perpendicular to the field. Profiles of pH variation across the gel, measured by video photography, indicate that the anisotropic patterns appear when the H+ and OH- ions, migrating in opposite directions, meet. Calculations of pH profiles using a model based on electrodiffusion reproduce several features of measured pH profiles, including the power-law dependence on the electric field of the time at which the oppositely charged fronts meet. Ions migrating from both ends of the gel produce pH changes that are correlated with macroscopic shrinking and orientation of the gel.

Isotropic-nematic spinodal decomposition kinetics

The initial stage of isotropic-nematic spinodal demixing kinetics of suspensions of very long and thin, stiff, repulsive rods is analyzed on the basis of the N-particle Smoluchowski equation. Equations of motion for the reduced probability density function of the position and orientation of a rod are expanded up to second order in spatial gradients and leading order in orientational order parameter. The resulting equation of motion is solved analytically, from which the temporal evolution of light-scattering patterns are calculated. It is shown that inhomogeneities in number density are enslaved by the temporal development of inhomogeneities in orientational order. Furthermore, demixing due to rotational diffusion is shown to be much faster as compared to translational diffusion. This results in an instable mode that is rotational, for which the corresponding eigenvector remains finite at zero wave vector. The scattered intensity nevertheless exhibits a maximum at a finite wave vector due to the wave-vector dependence of time-exponential prefactors. The wave vector where the intensity exhibits a maximum is therefore predicted to be a function of time even during the initial stage of demixing.

3-D simulation of light scattering from biological cells and cell differentiation

A 3-D code for solving the set of Maxwell equations with the finite-difference time-domain method is developed for simulating the propagation and scattering of light in biological cells under realistic conditions. The numerical techniques employed in this code include the Yee algorithm, absorbing boundary conditions, the total field/scattered field formulation, the discrete Fourier transformation, and the near-to-far field transform using the equivalent electric and magnetic currents. The code is capable of simulating light scattering from any real cells with complex internal structure at all angles, including backward scattering. The features of the scattered light patterns in different situations are studied in detail with the objective of optimizing the performance of cell diagnostics employing cytometry. A strategy for determining the optimal angle for measuring side scattered light is suggested. It is shown that cells with slight differences in their intrastructure can be distinguished with two-parameter cytometry by measuring the side scattered light at optimal angles.

Multivariate analysis and classification of two-dimensional angular optical scattering patterns from aggregates

Two-dimensional light-scattering patterns from aggregates have undergone feature extraction followed by multivariate statistical analysis. The aggregates are comprised of primary particles of varying shape and size. Morphological descriptors (features) were extracted by a nonlinear filtering algorithm (spectrum enhancement) and then processed by principal component analysis and discriminant function analysis. The analysis was performed on two data sets, one in which the aggregates had a fixed primary particle size but varied in overall dimension and another in which the aggregate size was fixed but the primary particle size varied. Classification of the samples was performed adequately, providing some distinction among the limited classes that were analyzed.

Development of Measurement System for Diameter and Refractive Index of Silk Fibroin Filament Based on Scattered Light Pattern

Development of Measurement System for Diameter and Refractive Index of Silk Fibroin Filament Based on Scattered Light Pattern

Automatic 3D-Laser Scattering Measurement for Ultra-Finished Surface with Nanowatt Sensitivity

Automatic measurement system that can evaluate laser scattering from an ultra-finished surface has been developed. The system uses Ar+laser as an illumination source, and a highly sensitive photomultiplier tube (PMT) for detecting scattered light. The major feature of the developed system is that the 3-dimensional distribution of scattered light from a scatterer is obtained by rotating the detector using two motor-driven rotation stages. The feasibility of this system is demonstrated by measuring light scattered from oxide silicon surfaces containing a microscratch and polystyrene latex (PSL) sphere. Experimental results show that the spatial scattering light intensity pattern can be obtained with nanowatt sensitivity, and shows that scattered light patterns for each scatterer are distinctive. This measurement system is thus expected to become an effective tool to characterize ultra-finished surfaces, such as a post-chemical mechanical polishing (CMP) wafer surface, from the pattern of detected scattered light intensity.

Kinetics of the initial stage of immunoagglutionation studied with the scanning flow cytometer

The use of a scanning flow cytometer (SFC) to study the evolution of monomers, dimers and higher multimers of latex particles at the initial stage of the immunoagglutination is described. The SFC can measure the light-scattering pattern (indicatrix) of an individual particle over an angular range of 10–60°. A comparison of the experimentally measured and theoretically calculated indicatrices allows one to discriminate different types of latex particles (i.e. monomers, dimers, etc.) and, therefore, to study the evolution of immunoagglutination process. Validity of the approach was verified by simultaneous measurements of light-scattering patterns and fluorescence from individual polymer particles. Immunoagglutination was initiated by mixing bovine serum albumin (BSA)-covered latex particles (of 1.8 μm in diameter) with anti-BSA IgG. The analysis of experimental data was performed on the basis of a mathematical model of diffusion-limited immunoagglutination aggregation with a steric factor. The steric factor was determined by the size and the number of binding sites on the surface of a latex particle. The obtained data are in good agreement with the proposed mathematical modeling.

Microscopic origin of light scattering in tissue.

A newly designed instrument, the static light-scattering (SLS) microscope, which combines light microscopy with SLS, enables us to characterize local light-scattering patterns of thin tissue sections. Each measurement is performed with an illumination beam of 70-microm diameter. On these length scales, tissue is not homogeneous. Both structural ordering and small heterogeneities contribute to the scattering signal. Raw SLS data consist of a two-dimensional intensity distribution map I(theta, phi), showing the dependence of the scattered intensity I on the scattering angle theta and the azimuthal angle phi. In contrast to the majority of experiments and to simulations that consider only the scattering angle, we additionally perform an analysis of the azimuthal dependence I(phi). We estimate different contributions to the azimuthal scattering variation and show that a significant fraction of the azimuthal amplitude is the result of tissue structure. As a demonstration of the importance of the structure-dependent part of the azimuthal signal, we show that this function of the scattered light alone can be used to classify tissue types with surprisingly high specificity and sensitivity.

Nucleation Behavior of n-Alkane Microdroplets in an Electrodynamic Balance

The nucleation behavior of n-alkane droplets with carbon numbers ranging from 14 to 17 was observed in an electrodynamic balance. Changes in the elastic light-scattering pattern of the single levitated microdroplets indicate the phase transition from liquid to solid. Cooling/heating experiments showed larger supercooling temperatures than expected for alkane droplets with an alkane/air interface. Measurements of the nucleation rates of C15H32 and C17H36 gave additional information about the dynamics of the nucleation process and allowed us to distinguish homogeneous from heterogeneous nucleation.

Development of a surface roughness measurement system using reflected laser beam

The scattered light pattern reflected from a machined surface generally contains much information concerning the surface roughness. This study examines and proposes a surface roughness measurement technique for the on-machine measurement of the roughness of machined surfaces. The technique is based on the measurement of scattered light patterns and the statistical analysis of the light intensity distribution. Scattered light patterns spread out narrowly in a direction vertical to the tiny scratches on the machined surface caused by tools. The deeper the scratch, the more dispersion there is, which indicates a rougher surface. The standard deviation of the scattered light pattern is nearly in proportion to the surface roughness. Measurements obtained using this method are within 10% of those obtained using a common contact method. Therefore, the proposed method is thought to be effective for use when a quick measurement is needed when a workpiece is fixed onto the machine.

Segmental Orientation in Uniaxially Deformed Polymer Networks and Application to Orientation-Induced Crystallization

An orientational distribution function is employed for the first time to describe segmental orientation in a uniaxially deformed network. The model assumes that each chain expands between two active junctions that displace affinely with the macroscopic deformation. The model was first introduced by Erman et al. and used to evaluate the second-order Legendre polynomial of the segment orientation. This paper extends their model to compute the orientation factors of a single segment up to the eighth order, thereby enabling a more complete description of the orientational distribution to be estimated. As an application of these results to oriented crystallization of polymeric systems, an evaluation of the orientational distribution function for crystallites in a polyethylene film manufactured by a calendering method is presented. The resulting theoretical distribution of the crystallites is in good agreement with the experimental function measured by X-ray diffraction techniques. Furthermore, the small-angle light-scattering pattern under Hv polarization was estimated by assuming a rod to be an aggregation of cylindrical clusters oriented with a kinetically determined distribution. The calculated light-scattering patterns are also in good agreement with the observed ones.

Scattered Light Models of Protostellar Envelopes: Multiple Outflow Cavities and Misaligned Circumstellar Disks

Ground-based imaging, imaging polarimetry, and recent Hubble Space Telescope WFPC2 and NICMOS images of protostars have revealed very complex scattered light patterns that cannot be entirely explained by two-dimensional radiation transfer models. We present here for the first time radiation transfer models of T Tau and IRAS 04016+2610 that are fully three-dimensional, with the aim of investigating the effects on image morphology of multiple illuminating sources and infalling envelopes that have been shaped by multiple outflows. For T Tau we have constructed scattered light models where the illumination of the surrounding envelope is by a binary, with each source surrounded by its own small circumstellar disk or envelope. We find that the asymmetries in the WFPC2 image of T Tau can be reproduced if the disks in the binary system are misaligned, consistent with a recently discovered bipolar outflow believed to originate from the secondary. For IRAS 04016+2610 we find that the observed scattered light pattern can be reproduced by scattering in an envelope with cavities carved by two sets of bipolar outflows, suggestive of an embedded binary system.

Phase Inversion of Polybutadiene/Polyisoprene Blends under Quiescent and Shear Conditions

We investigate the effect of phase inversion on the domain morphology and rheological properties of phase-separated polybutadiene/polyisoprene blends using optical microscopy, light scattering, and rheometry. Two different blends, low-vinyl polybutadiene/low-vinyl polyisoprene (LPB/LPI) and low-vinyl polybutadiene/high-vinyl polyisoprene (LPB/HPI), were used in this study. The LPB/LPI blend has a lower critical solution temperature (LCST) of (62 ± 1) °C, while the LPB/HPI blend exhibits upper-critical-solution-temperature (UCST) behavior with a critical temperature above the experimentally accessible temperature window. We determine the quiescent phase-inversion composition (φLPI = 0.55 ± 0.05) of phase-separated LPB/LPI blends from the discontinuity in the dynamic storage modulus and shear viscosity. For LPB/HPI, we find that a shear-induced coexisting structure (apparent as a “walnutlike” light-scattering pattern) develops at a fixed composition (φHPI = 0.8) and constant temperature. The coexisting morphology consists of two different anisotropic structures; stringlike domains and small (ξ < 5 μm) vorticity-aligned domains. We suggest that shear-induced phase inversion may lie at the foundation of this effect, although more theoretical and experimental work is needed to verify this.

Diameter and Refractive Index of a Cylindrical Thread Determined by Scattered Light Pattern

We have devised a method of determining the optimal value of both the refractive index n and the diameter D of a transparent cylinder by the scattering intensity pattern over a wide range of scattering angle. We have shown that the method is stable to small variations of data for the sample with D#x2272;10#x03BB; (wavelength) and could specifically determine the parameters of a spider#x0027;s thread as n = 1.520 (#x2212;0.033, #x002B;0.033), D=0.564 (#x2212;0.009, #x002B;0.011)#x03BC;m for #x03BB; = 632.8 nm.

Calibration-free method to determine the size and hemoglobin concentration of individual red blood cells from light scattering

At present, hemoglobin concentration and the volume of an erythrocyte can be determined from the intensities of light scattered by an individual cell at fixed angular intervals. This method is used in modern hemoglobin analyzers, but it requires calibration of optical and electronic units by certified particles of known size and refractive index. We describe a method that is based on the parametric solution of an inverse light-scattering problem and does not require a calibration procedure. The method is based on the use of parameters of the entire angular light-scattering pattern, called an indicatrix here. These parameters do not depend on the absolute intensity of light scattering. The indicatrix parameters form approximating equations that relate these parameters to the size and the phase-shift parameters of the particle. The applicability of the method is demonstrated by measurement of the indicatrices of individual sphered erythrocytes. The indicatrices of the individual erythrocytes were measured with a scanning flow cytometer at an angular range of from 15 to 55 deg. The volume and the hemoglobin concentration have been calculated by use of the developed method and by fitting of the experimental indicatrices to the indicatrices calculated from the Mie theory.

Memorized polarization-dependent light scattering in rare-earth-ion-doped glass

We report the observation of memorized polarization-dependent light scattering in a Eu2+-doped fluoroaluminate glass sample. Anisotropic light scattering along the plane of the light polarization was observed in the glass sample after the excitation of a focused 800 nm, 150 fs laser beam at a repetition rate of 200 kHz. When we changed the direction of the light polarization and irradiated the same location, we observed an anisotropic light-scattering pattern identical to the original one at the beginning, but then observed a new pattern along the new direction of the light polarization while the original light-scattering pattern disappeared gradually with the passage of time. This observed phenomenon was considered to be due to the light scattering of the polarization-dependent permanent microstructure induced by the polarized ultrashort pulsed laser itself.

Polarized laser light scattering applied to surface morphology characterization of epitaxial III–V semiconductor layers

In this paper, we analyze typical morphologies of epitaxial III–V semiconductor layers by using a polarized laser light scattering technique. Crosshatched topographies, which are developed during heteroepitaxial growth, are studied. A sample with an intentionally high density of oval defects is also explored to establish how the laser light scattering pattern is affected by the presence of these defects, which are unavoidable in the epitaxial layers grown by molecular beam epitaxy. The former topographies produce a scattered light pattern that is highly anisotropic, with the intensity concentrated along two preferential directions; the latter defects give rise to a fairly isotropic pattern. Employing a perturbation-theoretical model, whose applicability and consistency are explicitly demonstrated by our results, the surface power spectral density is retrieved from the angle-resolved light scattering experimental data. For the samples exhibiting crosshatched topography, the scattering measurements provide information that allows us to model the roughness of the surface in terms of two quasi-one-dimensional, anisotropic components, and one two-dimensional, isotropic, long-range background. The root mean square heights and the typical lateral distances between ridges are obtained in quantitative agreement with the values extracted from the atomic force microscopy measurements. For the sample presenting oval defects, we consider their contribution to the surface power spectral density by means of a simple model of randomly distributed particles on a surface, and we compare the resulting power spectral density with typical behavior found in the literature for good-morphology GaAs layers. With the help of the ex situ information thus obtained, we also discuss the implementation of the light scattering technique for in situ monitoring during epitaxial growth.

Particle Sizing in a Flow Environment Using Light Scattering Patterns

Particle Sizing in a Flow Environment Using Light Scattering Patterns

Relaxation Behavior of Polymer Blends after the Cessation of Shear

We investigated the relaxation of a binary polybutadiene/polyisoprene blend after the cessation of steady-state shear using both in situ optical microscopy (OM) and light scattering (LS). Through fast Fourier transforms of the micrographs, we were able to directly relate our LS patterns with the real space morphology. In the steady state we observed ellipsoidal domains and strings. Upon the cessation of shear, these morphologies relaxed to the equilibrium morphology via a variety of mechanisms. After low shear rates were applied, coalescence between domains of random spatial distribution occurred. If the shear rate previously applied was sufficiently high, the strings were found to break up into small droplets forming necklace-like structures. The nonrandom spatial distribution created by shearing resulted in a long-lasting anisotropy at rest. If the previously applied shear rate was further increased, thermodynamic effects became important and anisotropies relaxed very fast as a consequence. A spinodal pattern in both real space and in the LS patterns was found to occur during the relaxation process.

Particle classification from light scattering with the scanning flow cytometer.

The differential light-scattering pattern, an indicatrix, provides the most complete characterization of the optical properties of a particle. Particle classification can be performed on the basis of particle parameters retrieved from the indicatrices. This classification extends the ability of flow cytometry in particle recognition. The scanning flow cytometer (SFC) permits an acquisition of traces of light scattering signals, i.e., native SFC traces, from single particles. The acquired native SFC traces are transformed into indicatrices. The performance of the SFC in measurements of indicatrices has been demonstrated for the following particles: lymphocytes, erythrocytes, polystyrene particles, and milk-fat particles. The structure and profile of the indicatrix for each particle type have been found to be unique. Classification of polystyrene particles has been performed on the basis of the map formed by particle refractive index and size. The polystyrene particles were classified using this map into different size categories ranging from 1.4-7 microm, with a size deviation of 0.07 microm. The method based on analysis of native SFC traces shows better performance in particle classification than the method based on the particle refractive index and size map. The classification performance of the SFC will be useful, for example, for particle sorting and particle identification, and with additional fluorescent measurements may have applications in multiparameter particle-based immunoassay.