Showing papers on "Dynamic light scattering published in 1991"

Laser Light Scattering: Basic Principles and Practice

Abstract: Light scattering theory optical mixing spectroscopy photon correlation spectroscopy interferometry experimental methods methods of data analysis characterization of polymer molecular weight distribution (particle sizing).

Micelle and Gel Formation in a Poly (ethylene oxide)/ Poly (propylene oxide)/ Poly (ethylene oxide) Triblock Copolymer in Water Solution. Dynamic and Static Light Scattering and Oscillatory Shear Measurements

Abstract: The properties of aqueous solutions of low molecular weight triblock copolymers of PEO/PPO/PEO have been investigated, mainly by dynamic and static light scattering. At low concentrations (C<10%) and temperature (<25°C) the relaxation time distributions from dynamic light scattering show the coexistence of the monomer (R H =18 A), micelles (R H =80 A), and micellar aggregates in relative proportions which depend critically on temperature and concentration

Multiple Light-Scattering Probes of Foam Structure and Dynamics

Abstract: The structure and dynamics of three-dimensional foams are probed quantitatively by exploiting the strong multiple scattering of light that gives foams their familiar white color. Approximating the propagation of light as a diffusion process, transmission measurements provide a direct probe of the average bubble size. A model for dynamic light scattering is developed that can be used to interpret temporal fluctuations in the intensity of multiply scattered light. The results identify previously unrecognized internal dynamics of the foam bubbles. These light-scattering techniques are direct, noninvasive probes of bulk foams and therefore should find wide use in the study of their properties.

Dynamic light-scattering study of the glass transition in a colloidal suspension.

Abstract: This paper describes a light-scattering study of the glass transition in nonaqueous suspensions of sterically stabilized colloidal spheres. The observed phase behavior, fluid, crystal, and glass, is consistent with an essentially hard-sphere interaction between the particles. Metastable fluid states were obtained upon shear melting the crystalline phases by tumbling the samples. Their intermediate scattering functions, measured by dynamic light scattering, showed the emergence of a nondecaying component, implying structural arrest, at essentially the same concentration as that at which homogeneously nucleated crystallization was no longer observed. The overall forms of the intermediate scattering functions are consistent with the predictions of mode-coupling theories for the glass transition. Supplementary studies of the static structure factors indicated only short-ranged spatial order for particle concentrations ranging from the equilibrium fluid through the metastable fluid to the glass.

Suppression of Multiple Scattering by Photon Cross-correlation Techniques

Abstract: With growing scientific interest in concentrated colloidal systems, multiple scattering becomes a major obstacle in many light-scattering experiments. Stimulated by work of Phillies and Drewel, three different dual-beam dual-detector dynamic light scattering experiments are discussed, which all achieve the isolation of singly scattered light by photon cross-correlation. All three experiments allow for a large variation of the scattering angle—an important requirement for studies of interacting systems.

Rotational and translational diffusion of short rodlike molecules in solution: Oligonucleotides

Abstract: Rotational and translational diffusion coefficients in aqueous solution of a series of three B duplex oligonucleotides 8, 12, and 20 base pairs in length are measured by depolarized and polarized dynamic light scattering, respectively. Theoretical relations for the diffusion coefficients of short rods by Tirado and Garcia de la Torre are used in combination with the experimental data to obtain the dimensions of the molecules. The theoretical relations are self‐consistent through the series and give a hydrodynamic diameter for DNA of 20±1.5 A. The results, furthermore, show that the combination of depolarized and polarized dynamic light scattering provides a powerful method for obtaining hydrodynamic dimensions of short rodlike particles and may therefore be used in applications which follow molecular sizes and size changes.

Nonergodicity parameters of colloidal glasses.

Abstract: Nonergodicity parameters, the nondecaying components of the coherent intermediate scattering functions, of «hard-sphere» colloidal glasses were measured by dynamic light scattering. These agree reasonably well with the predictions of mode-coupling theory for hard-sphere atoms, with no adjustable parameters in the comparison. In addition, we provide further verification of the recently developed theory of dynamic light scattering by nonergodic media

Dynamic light scattering study of internal motions of polymer coils in dilute solution

Abstract: Internal motions of a high molecular weight (M, = 8.12 X lo6) polystyrene with a narrow distribution of M,/M, 5 1.04 in benzene has been studied by dynamic light scattering. By means of a prism-cell light-scattering spectrometer, the translational diffusion of the center of mass of the polymer coil has been precisely determined at KR, 1, indicating that the polymer chain dynamics could be described in terms of the non-free-draining model. Extraction of information on the internal motions was made by comparing the CONTIN output line-width distributions from the experimental data with those from the simulated data based on a theoretical model for polymer coils in the non-free- draining limit. By selecting appropriate KR, ranges, the first two internal relaxation times could be obtained. At regimes of 1 5 x 5 3 and 3 5 x 5 6, where z = (KR,)*, the first internal relaxation time T~ (the longest one) and the second internal relaxation time 72 were determined, respectively. To our knowledge, for a flexible polymer coil in solution, 72 was determined experimentally for the first time. The experimental observations agreed very well with the theoretical predictions based on polymer chain dynamics with hydrodynamic interactions. I. Introduction The dynamics of polymer chains in dilute solution is one of the fundamental problems in polymer physics. The theory of dynamic properties of flexible polymer chains has been developed by Rouse' and Zimm,2 Le., the well- known Rouse-Zimm (RZ) model. Experimental advances in investigating the dynamics of flexible polymers in solution have been made possible partially by the devel- opments of better dynamic light scattering instrumenta- tion and of more sophisticated methods of data analy~is.~-~ The RZ model has been applied to dynamic light scattering studies by Pecora,'j de Genne~,~ and DuBois-Violette8 who established forms for the dynamic structure factor S(K,t). In the region KR, << 1 with K (= (4~rz/Xo) sin (19/2)) and R, being, respectively, the scattering vector and the radius of gyration of the polymer chains, the contribution to S(K,t) is mainly from the translational diffusion of the center of mass of the polymer chains. Thus, S(K,t) at KR, << 1 and for monodisperse polymer coils has a single exponential form. In the intermediate KR, range with KR, L 1 and even for monodisperse polymer chains, S(K,t) becomes multiexponential due to significant contributions from various internal motions. Investigation of intramo- lecular internal motions in the polymer chain having internal degrees of freedom is of particular interest because such studies may permit us to obtain information on the flexibility parameter for flexible and semiflexible polymers. However, study of internal motions in dilute polymer solutions has remained a difficult experimental problem especially when a proper interpretation of S(K,t) needs an appropriate theoretical model.g Akcasu et a1.l0 have developed a method for the interpretation of dynamic light scattering data over the entire accessible K range in terms of the first cumulant Q(K) of S(K,t) which is the initial slope of S(K,t) and can be determined by the cumulants analysisll of S(K,t). This practical approach is quite useful in testing the dynamic

Coated droplet model of microemulsions: Optical matching and polydispersity

Abstract: Dilute water‐in‐oil microemulsions, such as the ternary system water–AOT–hexane, can be modeled as suspensions of spherical droplets coated with surfactant. There is a general agreement that the radius of the droplets is not uniform but the magnitude of the polydispersity is subject to discussions. The polydispersity influences strongly optical properties of the microemulsions, in particular it determines the characteristic features of scattering data observed in the vicinity of optical matching. We present here analytical expressions and data for the refractive index increment, the average scattering intensity, the apparent hydrodynamic radius, and the second cumulant of dynamic light scattering. Our model reproduces without any free parameters the dependence of the refractive index increment on the water‐to‐surfactant ratio ω. Only two free parameters are needed to fit the ω dependence of the other three quantities: δ represents approximately the thickness of the surfactant layer and γ=〈r 2〉/〈r〉2−1 refl...

The microstructure of polydisperse, charged colloidal suspensions by light and neutron scattering

Abstract: Structure measurements of a suspension of charged polystyrene spheres with significant polydispersity (16%) are reported for a wide range of particle and added salt concentrations and scattering wave vector. Small angle neutron scattering yielded the structure factors of concentrated samples that have had extensive rheological characterization. A Schulz distribution was used as a model of the particle size distribution to reduce the intensity data and as a basis for the theoretical fits of the structure factors. Static light scattering measurements yielded the structure factors of diluted, deionized samples. Dynamic light scattering was also performed to study the relaxation of these structures. These measured structures were fit with a recent theory that accounts for both size and charge polydispersity in the suspension. These results and the previous extensive, rheological investigations and physical characterization yield a complete data set on a well‐characterized, model system that can be used to tes...

Characterisation of adsorbed layers of a disordered coil protein on polystyrene latex

Abstract: The combined use of small-angle X-ray scattering (SAXS) and photon correlation spectroscopy (PCS) to characterise adsorbed layers of β-casein at the solid/liquid interface is reported. The protein was adsorbed to polystyrene latex particles at room temperature, low ionic strength and neutral pH and adsorption densities assessed by a solution-depletion technique which showed a plateau in the adsorption. Results from the SAXS experiments were analysed to provide electron-density profiles. These were backed up with results from PCS which provided hydrodynamic thicknesses over the range of the adsorption isotherm. This information, together with calculated hydrophobicity and charge profiles for the protein, yielded a molecular model for the adsorbed layer. Although β-casein in solution has a largely randon coil conformation, it appears to adopt a much more compact form when it is adsorbed on polystyrene latex. Most of the protein lies close to the surface, leaving part of the chain extended into the aqueous phase. The most likely candidate for the extended chain is part of the highly charged sequence of 40 or so amino acids at the N terminus of the protein. The hydrodynamic thickness of the protein layers increases with adsorbed concentration of protein. The thicknesses reached are substantially greater than those predicted by theories of self-avoiding walks of the extended chain with volume exclusion interactions included and it is suggested that long-range electrostatic repulsive forces are involved.

Particle Sizing by Photon Correlation Spectroscopy. Part II: Average values

Abstract: The average values of the diameters and the diffusion coefficients of non-interacting homogeneous spherical particles as obtained with photon correlation spectroscopy are reviewed. In general, the average diffusion coefficients calculated from the first cumulant can be identified as intensity averages, while the average particle diameters are harmonic intensity averages. For particles with linear dimensions that are small compared to the wavelength of light, the intensity averages can be identified as z-averages for the diffusion coefficient and as harmonic z-averages for the diameter. For larger particles the intensity averages are, however, different from the z-averages and are dependent on the material examined (relative refractive index) and on the experimental equipment used (laser wavelength and state of polarization and scattering angle).

Light-scattering study on the fractal aggregates of polystyrene spheres: Kinetic and structural approaches

Abstract: Static and dynamic light-scattering measurements on the fractal aggregates of polystyrene spheres (diameter=40 nm), induced by the addition of salt (0.2–1.5 mol·dm−3NaCl) at a constant pH of 9.2, are presented. The kinetic approach with the use of dynamic light scattering enables us to distinguish between fast and slow aggregation and the structural approach by using static light scattering provides us an appropriate way to determine the fractal dimension. By using the DLVO colloid stability theory to calculate the potential energy curves between polystyrene spheres at various salt concentrations we have concluded that the interparticle interactions would not only govern the kinetic growth of clusters, but also determine the fractal structure and the degree of cluster restructuring. In the category of fast aggregation, the smaller the interparticle attraction in the primary minimum, the larger the fractal dimension resulted from restructuring.

Neutron, X-ray and light scattering : introduction to an investigative tool for colloidal and polymeric systems : proceedings of the European Workshop on Neutron, X-Ray and Light Scattering as an Investigative Tool for Colloidal and Polymeric Systems, Bombannes, France, 27 May - 2 June, 1990

Abstract: Preface. Part I: Using General Principles . Introduction to scattering experiments (J.P. Cotton). Initial data treatment (J.P. Cotton). Small-angle scattering and light scattering (O. Glatter). General theorems of small-angle scattering by disperse systems (D.I. Svergun). Part II: Solving Inverse Problems . Contrast variation in X-ray and neutron scattering (C.E. Williams). Label triangulation (R.E. May). Interacting monodisperse and polydisperse spheres (L. Belloni). Chord analysis (D. Tchoubar). Part III: Studying Surfaces and Interfaces Scattering of connected networks (Th. Zemb). Scattering by interfaces: variations on Porod's law (L. Auvray and P. Auroy). Data interpretation in specular neutron reflection (J. Penfold). Part IV: Focussing on Large Scales . Structure of colloidal crystals by scattering (P.N. Pusey). Growth: a brief guide for the use of scattering techniques (B. Cabane). Part V: Investigating Non-Equilibrium Systems . Steady-state SANS experiments under external constraints (P. Lindner). Time resolved small angle X-ray experiments (C. Riekel). Part VI: Using Light . Basic concepts in static and dynamic light scattering: application to colloids and polymers (M. Hofer). Dynamic light scattering: data analysis and applications to some biological systems (J. Langowski and R. Bryan). Dictionary. Author index. Subject index.

Collective diffusion of charged spheres in the presence of hydrodynamic interaction

Abstract: The short-time behavior of the scattering intensity, which can be measured by dynamic light scattering, is investigated theoretically. We consider a monodisperse system of charged hard spheres and study the combined effects of electrostatic repulsion and hydrodynamic interactions. The electrostatic repulsion determines the static properties, which are calculated from the thermodynamically consistent Rogers-Young scheme. For comparison, some results obtained within the rescaled mean spherical approximation (RMSA) are shown as well. Many-body hydrodynamic interaction is treated within the renormalization approach due to Beenakker. We compare results depending on the scattering vector to experimental data. Further, we show various trends for the collective diffusion coefficient, which is obtained as the long wavelength limit of the collective diffusion function, when volume fraction of spheres, salinity, and charge of the spheres are changed. The results are aimed at the interpretation of dynamic light scattering properties of systems of weakly charged spheres, which could be ionic micelies or macromolecules at moderate concentrations.

Structural properties of polydisperse biopolymer solutions: A light scattering study of bovine α‐crystallin

Abstract: We have measured mean value of RHz, mean value of R2G1/2z, and mean value of Mw for individual fractions of the protein alpha-crystallin obtained by gel filtration of bovine lens nuclear extracts. A strong and monotonic decrease of mean value of RHz and mean value of Mw with increasing elution volume could be observed, indicating a broad size distribution. The experimental results are quantitatively consistent with a polymerization of monomeric units into linear chains, which may have a certain degree of flexibility. Using theoretical expressions for mean value of R2G and mean value of RH originally derived for semiflexible polymers in solution, we can self-consistently analyse the data from static and dynamic light scattering, and from electron microscopy experiments. We thus obtain detailed information on the molecular weight distribution and the quaternary structure of alpha-crystallin in these solutions.

Dynamic light scattering, mutual diffusion, and linear viscoelasticity of polymer solutions

Abstract: A theoretical study of the dynamic light scattering spectrum from a binary solution consisting of a polymer and a small molecular weight solvent is carried out. The study is based upon a modified hydrodynamic equation previously derived from statistical mechanics by Bearman and Kirkwood for a multicomponent solution. The result shows that mutual diffusion arising from the osmotic pressure fluctuation and the viscoelasticity affecting mechanical properties of the polymer solution are, in general, mixed. The extent of mixing depends on the frequency and a coupling parameter β, which is proportional to the difference between the partial specific volume of the polymer and that of the small molecular solvent.At low frequency the coupling is negligible, and one obtains a diffusion equation with the mutual diffusion coefficient dependent only on the osmotic modulus. At the frequency in the plateau stress modulus region, the result predicts a cooperative diffusion coefficient which consists of both the osmotic mo...

Dynamic light scattering study of the sol-gel transition

Abstract: The poly(methyl methacrylate)/butyl acetate system was studied using quasielastic light scattering spectroscopy. Critical dynamical behaviour was observed near the sol-gel transition that is characterized by the presence of a power-law spectrum of relaxation times. The results were interpreted in terms of a simple cluster diffusion model. The experimental results favor the percolation model.