Suppression of Multiple Scattering in a Depolarized Light-Scattering Experiment Using the One-Beam Setup

We have performed depolarized dynamic light-scattering measurements of suspensions of colloidal spherical particles made of tetrafluoroethylene copolymerized with perfluoromethylvinylether (MFA). Measurements on highly concentrated turbid suspensions of 17 wt% MFA in water show that the one-beam cross-correlation technique successfully suppresses the multiple scattering contributions. This is the first time that a cross-correlation technique has been used in a depolarized scattering experiment.     

Dynamic light scattering in turbid colloidal dispersions: a comparison between the modified flat-cell light-scattering instrument and 3D dynamic light-scattering instrument

It remains a challenge to measure dynamics in dense colloidal systems. Multiple scattering and low light-transmission rates often hinder measurements in such systems. One of the well-established techniques for overcoming the problem of multiple scattering is cross-correlation techniques such as 3D dynamic light scattering (3D-DLS). However, a high degree of multiple scattering, i.e., vanishing single-scattering contribution in the signal, limits the use of the 3D-DLS technique. We present another approach to measure turbid media by way of upgrading our flat-cell light-scattering instrument (FCLSI). This instrument was originally designed for static light-scattering (SLS) experiments and is similar to a Fraunhofer setup, which features a flat sample cell. The thickness of the flat sample cell can be varied from 13 mum to 5 mm. The small thickness increases the transmission, reduces multiple scattering to a negligible amount, and therefore enables the investigation of dense colloidal systems. We upgraded this instrument for DLS measurements by the installation of an optical single-mode fiber detector in the forward scattering regime. We present our instrumentation and subsequently test its limits using a concentration series of a turbid colloidal suspension. We compare the performances of our modified flat-cell light-scattering instrument with that of standard DLS and with that of 3D-DLS. We show that 3D-DLS and FCLSI only have a comparable performance if the length of the light path in the sample using the 3D-DLS is reduced to a minimum. Otherwise, the FCLSI has some advantage.     

Three dimensional cross-correlation dynamic light scattering by non-ergodic turbid media

We investigate dynamic light scattering by non-ergodic turbid media with an adapted version of the method proposed by Pusey and van Megen [Physica A 157, 705 (1989)]. Our formulation follows the derivation of the original method by extending it to the three dimensional cross-correlation scheme (3DDLS). The main finding is an expression to obtain the dynamic structure factor from light scattering that takes into account the system turbidity and the peculiarities of the 3D geometry. From 3DDLS measurements in well-controlled solid-like systems of different turbidity, we confirm that our results can be interpreted reasonably well by the theoretical approach described here. Good agreement is found with earlier reported results on similar systems.     

Light Scattering Probes of Viscoelastic Fluids and Solids

In this article, we discuss recent advances in static and dynamic light scattering applied to soft materials. Special emphasis is given to light scattering methods that allow access to turbid and solid‐like systems, such as colloidal suspensions, emulsions, glasses, or gels. Based on a combination of single‐ and multispeckle detection schemes, it is now possible to cover an extended range of relaxation times from a few nanoseconds to minutes or hours and length scales below 1 nm up to several microns. The corresponding elastic properties of viscoelastic fluids or solid materials range roughly from below 1 Pa to several 100 kPa. Different applications are discussed such as light scattering from suspensions of highly charged colloidal particles, colloid and protein gels, as well as dense surfactant solutions.     

New trends in light scattering

In this article we review some of the most important new developments in light scattering that have emerged over the past 10 years. Some of the new methods substantially extend the range of accessible time and length scales. Different cross-correlation methods are now available to suppress multiple scattering over a large concentration range. Novel low coherent light sources on the other hand have stimulated progress in the field of heterodyne detection. Many of these new approaches take advantage of the nowadays available area detectors such as high resolution CCD/CMOS video cameras. This has enabled large scale parallel processing of speckle intensity fluctuations and in consequence has provided a wealth of possibilities in dynamic light scattering such as multi-speckle detection and time resolved correlation analysis.     

Static and dynamic light scattering in turbid suspensions

The application of static and dynamic light scattering to many colloidal systems of practical interest has often been considered too complicated due to strong multiple scattering. There are two new approaches to overcome this problem. One of them aims at suppressing contributions from multiple scattering using novel cross‐correlation schemes. While this relies on the suppression of multiple scattering, the so‐called diffusing wave spectroscopy (DWS) works in the limit of very strong multiple scattering. DWS can be used for the characterization of dynamic and static properties of colloidal systems on a large range of time and length scales ranging from a few Ångstroms to hundreds of nanometers. We demonstrate that a wealth of information can be obtained from these methods on the structure, dynamics, interaction effects, stability, aggregation, and sol‐gel transition in colloidal dispersions.     

Energy transfer and amplified spontaneous emission in temperature-controlled random scattering media

Hydroxypropyl cellulose (HPC) in aqueous solution forms nanoparticles and becomes highly scattering above its lower critical solution temperature (LCST approximately 41 degrees C). Enhancement of energy transfer (ET) and amplified spontaneous emission (ASE) have been observed in turbid HPC solutions containing Rhodamine 6G (RG) as an energy donor and Kiton Red 620 (KR) as an acceptor. A detailed analysis of self-absorption, absorption saturation, and multiple scattering effects has revealed the importance of photon diffusion in shutting down the intensity leakage. A 5-fold enhancement of ET in the turbid condition is estimated. Possible factors crucial for ET and ASE in random media are discussed, such as the donor-to-acceptor ASE energy pumping, the optical path elongation by multiple scattering, and the formation of "light pipes" in the near-field of the Mie scattering. The temperature-dependent colloidal formation is found to successfully control optical processes via multiple scattering with a sharp threshold and abrupt emergence of dense scatterers.     

Measurement of Continuous Particle Size Distributions of Finely Dispersed Powders by the Dynamic Light Scattering

Dispersity of finely dispersed powders with continuous bell-shaped particle size distributions is measured. The measurements are performed using two different dynamic light scattering instruments, a transmission electron microscope, and a sedimentograph equipped with an X-ray detector. Correlation functions measured with the dynamic light scattering instruments are processed using the CONTIN and KLUB software packages. Comparative analysis of the results obtained by different methods demonstrated that a reliable information on the dispersity of samples with wide particle size distributions can be obtained but using a combination of several analytical methods.     

Unusual formation of small aggregates by mixing giant multilamellar vesicles

The phase behavior and structure of aggregates in a hydrophobic block copolymer (L121)/double-tailed surfactant (AOT)/water system have been studied by phase study, fluorescence spectrometry, dynamic light scattering, transmission electron microscopy, small angle X-ray scattering (SAXS) and conductivity measurements. An isotropic, one-phase region is found between two biphasic regions containing large vesicles, namely, transparent samples are formed by mixing two turbid solutions. Depending on the AOT/L121 ratio, the isotropic region can be quite stable against temperature. The phase transition between the two regions can be detected by the used techniques, and structural transitions in the aggregates are inferred. The experimental evidence indicates that mixed aggregates are formed at very low concentrations, much lower than the critical micellar concentration of AOT. These micelle-like aggregates contain a mixed hydrophobic core, are small (2-4 nm), and seem to be quasi-spherical, which is an unexpected result since the packing parameters of the single amphiphiles do not favor such small quasi-spherical shapes. This behavior might have interesting implications in the release of substances from vesicles when their structure is disrupted.     

Light Scattering Study of Turbid Heat-Set Globular Protein Gels Using Cross-Correlation Dynamic Light Scattering

The structure factor of aqueous solutions of the globular protein β-lactoglobulin was determined as a function of heating time at 76°C. We show how the effect of multiple scattering on the scattered light intensity can be effectively corrected using cross-correlation dynamic light scattering even if the transmission is only 1%. The structure factor of aggregated and gelled proteins can be described by the Ornstein–Zernike equation. The system is characterized by a correlation length that increases with heating time and stabilizes some time after the gel is formed. The correlation length of the protein gels decreases with decreasing concentration. Measurements after progressive dilution of a sample close to the gel point showed that the protein aggregates are initially interpenetrated and disinterpenetrate upon dilution.     

Determination of the Monodisperse Mark-Houwink Equation of High-Vinyl Polybutadiene by Gel Chromatography and Light Scattering

Abstract

Gel chromatographic, light scattering, viscosimetric and osmotic pressure measurements have been made for high vinyl polybutadiene fractions and whole polymer. Three alternative methods for deducing a monodisperse Mark-Houwink equation from gel chromatographic, light scattering and viscosimetric data of samples with unequal distribution widths are suggested. The monodisperse Mark-Houwink equations obtained by these methods for high vinyl poly(butadiene) are all alike.     

Homogeneous immunoassay based on aggregation of antibody-functionalized gold nanoparticles coupled with light scattering detection

A universal platform of homogeneous noncompetitive immunoassay, using human immunoglobulin (IgG) as a model analyte, has been developed. The assay is based on aggregation of antibody-functionalized gold nanoparticles directed by the immunoreaction coupled with light scattering detection with a common spectrofluorimeter. In phosphate buffer (pH 7.0) solution, the light scattering intensity of the gold nanoparticles functionalized with goat-anti-human IgG can be greatly enhanced by addition of the human IgG. Based on this phenomenon, a wide dynamic range of 0.05-10 microg ml(-1) for determination of human IgG can be obtained, and the detection limit can reach 10 ng ml(-1). The proposed immunoassay can be accomplished in a homogeneous solution with one-step operation within 10 min and has been successfully applied to the determination of human IgG in serum samples, in which the results are well consistent with those of the enzyme-linked immunosorbent assay (ELISA), indicating its high selectivity and practicality. Therefore, the gold nanoparticle-based light scattering method can be used as a model to establish the general methods for protein assay in the fields of molecular biology and clinical diagnostics.     

Novel memory effect found in nematic liquid crystal/fine particle system

Novel liquid crystalline composites composed of a nematic two-frequency-addressing liquid crystal and organized clay mineral (about 1 wt %) have been prepared. The particles of clay mineral were dispersed homogeneously in the liquid crystal. The composite cells became transparent within 50ms when a 60 Hz electric field was applied. The transparent state was maintained after the field was switched off. It transformed into a turbid light scattering state by applying 1.5 kHz electric field which caused dynamic scattering in the cell. The light transmittance of both memory states did not change after 20 h without the electric field.     

Characterization of Enzymatically Induced Aggregation of Casein Micelles in Natural Concentration by in Situ Static Light Scattering and Ultra Low Shear Viscosimetry

The aggregation of casein micelles in undiluted skim milk after the addition of chymosin was studied by static light scattering and ultra low shear viscometry. The static light scattering measurements were made with two different sample thicknesses, 72 and 16 μm. The scattering data were analyzed by indirect Fourier transformation and by the polydispersity inversion technique which led to pair distance distribution functions and size distribution function, respectively. The minimum scattering angle was 1 degrees, which allows for the determination of particle sizes up to a maximum diameter of 12 μm. The fractal dimension determined from double logarithmic plots of intensity versus scattering vector resulted in values between 1.9 and 2.0. The influence of multiple scattering was determined by comparison of the measurements with the different sample thicknesses. The measurements show no significant influence of multiple scattering when the transmission is above 0.85. Due to the very complex and porous structure of the casein aggregates the Rayleigh-Debye-Gans scattering theory has been used in the data analysis. Measurements with a new instrument using ultra low shear showed good agreement with theory. Copyright 1999 Academic Press.     

Preparation,Characterisation and Properties of Nanocomposites Based on Epoxy Resins – An Overview

An overview about the use of nanoparticles in epoxy resins is given. Deaggregated fumed silica, sol gel materials and other spheroidic nanoparticles improved the abrasion resistance and the mechanical properties of filled epoxides, and several properties can be improved by specific particles. Combustion properties, strength and permeation can be improved by organically modified layered silicates. The proper characterisation of the nanocomposites is still an art. TEM analysis of the cured materials and light scattering with 3D cross-correlation for the liquid samples were sufficient methods for the characterisation of filled epoxides.     

Automation and Standardization—A Coupled Approach towards Reproducible Sample Preparation Protocols for Nanomaterial Analysis

Whereas the characterization of nanomaterials using different analytical techniques is often highly automated and standardized, the sample preparation that precedes it causes a bottleneck in nanomaterial analysis as it is performed manually. Usually, this pretreatment depends on the skills and experience of the analysts. Furthermore, adequate reporting of the sample preparation is often missing. In this overview, some solutions for techniques widely used in nano-analytics to overcome this problem are discussed. Two examples of sample preparation optimization by automation are presented, which demonstrate that this approach is leading to increased analytical confidence. Our first example is motivated by the need to exclude human bias and focuses on the development of automation in sample introduction. To this end, a robotic system has been developed, which can prepare stable and homogeneous nanomaterial suspensions amenable to a variety of well-established analytical methods, such as dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), field-flow fractionation (FFF) or single-particle inductively coupled mass spectrometry (sp-ICP-MS). Our second example addresses biological samples, such as cells exposed to nanomaterials, which are still challenging for reliable analysis. An air–liquid interface has been developed for the exposure of biological samples to nanomaterial-containing aerosols. The system exposes transmission electron microscopy (TEM) grids under reproducible conditions, whilst also allowing characterization of aerosol composition with mass spectrometry. Such an approach enables correlative measurements combining biological with physicochemical analysis. These case studies demonstrate that standardization and automation of sample preparation setups, combined with appropriate measurement processes and data reduction are crucial steps towards more reliable and reproducible data.     

Graphene Nanosheets and Quantum Dots: A Smart Material for Electrochemical Applications

A novel material for the electrochemical determination of endocrine disruptors using a composite based on graphene oxide modified with cadmium telluride quantum dots has been evaluated. The morphology, structure and electrochemical performance of the composite electrodes were characterised by transmission electron microscopy, dynamic light scattering, UV‐visible absorption spectra, fluorescence spectra, Raman spectra and cyclic voltammetry. The dynamic light scattering, transmission electronic microscopy and spectrophotometric measurements all showed good distribution of the quantum dots with a small particle size. The electrochemical measurements demonstrated the high performance of the composite response in the presence of a light source. Differential pulse voltammetry allowed the development of a method to determine 17β‐estradiol levels in the range from 0.2 to 4.0 μmol L ^?1 with a detection limit of 2.8 nmol L ^?1 (0.76 μg L ^?1).     

Effect of solvent composition on the association behavior of pectin in methanol-water mixtures

Turbidity, small-angle neutron scattering (SANS), and dynamic light scattering measurements have been carried out on semidilute systems of pectin in methanol-water media of various composition ratios. Structural and dynamical properties of pectin dissolved in water-methanol mixtures (case I) are compared with the corresponding conditions when pectin was dissolved in water before the prescribed amounts of methanol were added (case II). The turbidity rises as the percentage of methanol in the mixture increases and this trend is much stronger when the first procedure is used to dissolve pectin. The wavelength dependence of the turbidity indicates that larger association complexes are formed for the samples prepared according to case I. These findings indicate that at a given methanol-water composition, the preparation procedure in case I gives rise to poorer thermodynamic conditions of the system. Local structures probed by SANS experiments do not reveal any significant differences between the systems prepared by the two different procedures. The dynamic light scattering (DLS) results show that increasing methanol concentration in the mixture promotes the formation of association complexes and the disengagement relaxation time of individual chains or clusters is longer at higher percentage of methanol for case II. This can be attributed to stronger entanglement effects in case II. The features from DLS can be rationalized in the framework of the coupling model for constrained and interconnecting systems.     

Formation and Characterization of a Useful Biological Microemulsion System Using Mixed Oil (Ricebran and Isopropyl Myristate), Polyoxyethylene(2)oleyl Ether (Brij 92), Isopropyl Alcohol,and Water

A ‘biological microemulsion’ prepared using mixed oil (ricebran oil and isopropylmyristate), mixed amphiphiles (Brij 92 and isopropyl alcohol), and water has been studied with respect to phase behavior, shear viscosity, droplet dimension, and energetics of formation. The viscosity measured at different shear rates and temperatures has been analyzed for understanding the internal consistency of the system, and the activation parameters for its viscous flow. The hydrodynamic diameter, diffusion coefficient, and polydispersity of the dispersed droplets of both water-in-oil and oil-in-water samples have been determined from dynamic light scattering (DLS) experiments. The energetics of formation have been evaluated from calorimetric measurements.