Showing papers on "Dynamic light scattering published in 1980"

Light scattering in liquids and macromolecular solutions

Abstract: I: Colloid and Polymer Solutions.- Some Experiments Using Quasielastic Light Scattering.- Diffusion Coefficients in Colloidal and Polymeric Solutions.- On the Long Time Diffusion of Interacting Brownian Particles.- The Application of Brownian Dynamics to Photon Correlation Spectroscopy.- Light Scattering From Sterically Stabilized Silica Particles.- Depolarized Light Scattering from Concentrated Particle Suspensions.- Intramolecular Motion of Polystyrene.- II: Micelles, Thin Films and Biological Macromolecules.- Quasielastic Light Scattering Study of Intermicellar Interactions.- Stability and Fusion of Vesicles.- Light Scattering by Water in Oil Microemulsions.- Dynamic Light Scattering from Thin, Free, Liquid Films.- Techniques for Light Scattering from Hemeglobin.- Quasi-Elastic Light Scattering in the Measurement of the Motion of Flagellated Algae.- III: Phase Transitions and Hydrodynamic Instabilities.- Hydrodynamic and Critical Phenomena: Rayleigh-Benard Instability as a Critical Phenomenon and Critical Fluctuations Reduced by Shear, Both Related to Mean Field Behavior.- Interface Fluctuations of Growing Ice Crystals.- Buoyancy Driven Instabilities in Two Component Systems.- Thermodynamic Analysis of Inverted Bifurcation.- IV: Forced Raylexgh Scattering.- Forced Rayleigh Light Scattering in Fluids.- Study by Forced Rayleigh Scattering of Thermal Excitations in a Stratified Liquid Layer.- Forced Rayleight Scattering as Optoelastic Probe in SA Liquid Crystals.- Forced Rayleigh Scattering in a Critical Binary Liquid Mixture.

Dynamic light scattering studies of internal motions in DNA. II. Clean viral DNAs.

Abstract: Internal Brownian motions of clean ϕ29 and λ-DNAs have been studied using photon-correlation techniques at both visible (λ0 = 632.8 nm) and uv (λ0 = 363.8 nm) wavelengths. The present dynamic light scattering data, which extend to K2 = 19 × 1010 cm−2, can in every case be satisfactorily simulated by a Rouse-Zimm model polymer with an appropriate choice of the three model parameters. The effects of pH, salt concentration, single-strand breaks, and molecular weight on those model parameters have also been investigated. Intact clean DNAs exhibit surprisingly little variation with pH from 7.85 to 10.25, with salt concentration from 0.01 NaCl to 5.4M NH4Cl, or with molecular weight or GC content. The single-strand breaks have no effect at pH 9.46, but produce dramatic changes in the model parameters at pH 10.0 and 10.25, indicating the introduction of titratable joints at those pHs. The failure of either single-strand breaks or a large change in GC content to alter the model parameters in the neutral pH range is a strong indication that local denaturation is not required for those flexions and torsions that dominate the relaxation of fluctuations in the scattered light. The Langevin relaxation time for the slowest internal mode of a particular Rouse-Zimm model derived from the dynamic light scattering data is compared with pertinent literature data extrapolated to the same molecular weight. The present algorithm for determining model parameters from the light-scattering Dapp vs K2 curve actually yields a Langevin time in fairly good agreement with the literature value. For unknown reasons the light-scattering D0 values generally exceed those obtained from the molecular weight and sedimentation coefficient by about 20%.

On the nature of the slow modes appearing in quasi-elastic light scattering by semi-dilute polymer solutions

Abstract: 2014 We describe three series of experiments of quasi-elastic light scattering by semi-dilute solutions of polymers. By varying parameters such as the concentration, molecular mass, polymer structure, and the time interval between the solution preparation and the time of measurement, we are able to rule out a number of hypothesis about slow modes and to propose a qualitative interpretation of their origin. J. Physique 41 (1980) 519-523 JUIN 1980, Classification Physics Abstracts 36.20 Following the first papers of Pecora [l, 2] predicting that the spectrum of scattered light by long polymers should be composed of a large number of modes, a number of experimental papers [3-10] appeared, some reporting, the existence of several modes and some reporting the absence of several modes. From an experimental point of view, it can be said that the autocorrelation function of scattered light contains more than one mode if it cannot be fitted by a single exponential variation plus a base line. In the beginning, experimentalists looked for the modes due to internal relaxation processes predicted by Pecora, which have a smaller time constant than the translational mode. In fact, even for relatively low concentrations, long polymers also have a tendency to show interactions among chains which give rise to additional modes. De Gennes [11, 12, 13] et al. described the theoretical aspects of these semi-dilute solutions. Experiments were carried out based on several systems in different experimental conditions. Some showed the existence of several modes, others did not. Experimental data were then analysed in terms of a single mode or of two modes. Today following the work undertaken by de Gennes and the publications on semi-dilute solution [11-14], measurements (*) ERA C.N.R.S. 070 373. on single modes or on fast modes (i.e. the modes of smaller relaxation time) are well understood [15, 16, 18, 19, 22]. This is not the case for the existence and the properties of slow modes about which conflicting explanations are proposed [5-10, 17, 18, 19]. A possible reason for this situation may be the fact that in most cases the relevant parameters have not been varied. The purpose of this paper is to report three series of experiments which allow a number of proposed interpretations of slow modes to be ruled out. After a rapid description of the experimental methods and the data analysis, we describe each series of experiments from which specific conclusions can be drawn. Finally, we propose a model consistent with all the existing experimental evidence. The experimental apparatus is standard [20]. A laser beam illuminates a polymer solution and the scattered light is detected by a photomultiplier. We used homodyne detection and a digital autocorrelator. Experiments were done with three different systems. Polyadenilic acid in saline water is the system currently studied in our laboratory. Poly A is a polyelectrolyte and belongs to a series of systems (polynucleotides in saline water) in which slow modes have been reported. We also tested polystyrene in ethyl acetate with which experiments were done by Munch et al. [22]. Finally, we tested polystyrene in benzene, a polymer in a good solvent, for which slow modes have never been reported [15, 16, 22]. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:01980004106051900

Dynamic Light Scattering Study of Concentrated W/O Microemulsions

Abstract: Light beating spectroscopy experiments were performed on concentrated W/O microemulsions located in the vicinity of the gel phase on the phase diagram New results are reported: the most interesting feature is the non-exponential behaviour of the self-correlation function g (1)(K, τ) of the scattered field The initial decay rate of g (1)(K, τ) is not directly proportional to K 2; whereas the long time decay is found fairly exponential

Characterization of Particles During Growth in Emulsifier-Free Emulsion Polymerization of Styrene

Abstract: The emulsion polymerization of styrene in water in the absence of added surfactant has been studied by analyzing samples removed from the reaction vessels at various times. The particles present within these samples were characterized by electron microscopy, gravimetric analysis, gel permeation chromatography, conductometric titration and gas adsorption. During the early stages of reac tion, the number of particles decreased very rapidly to a level which then remained constant throughout the rest of the reaction. The particles in the early stages when N was decreasing appeared to consist mainly of polymer of about 1000 M.Wt., a small amount of high M.Wt. polymer was also present. The presence of this low molecular weight polymer may indicate that particle nucleation occurs either by the precipitation or micellization of low (500) M.Wt. oligomers. When N became constant, the growth of the particles was well described by a square law relationship between radius and time. The presence of particles of non-uniform electron density was noted and investigated. The particle nucleation was also studied using a combination of total intensity light scattering and photon correlation spectroscopy in a study of unstirred systems. The results indicated that in such unstirred systems, the particles were present as aggregates. The surface charge of the particles was found to decrease slowly between 20 – 30% conversion and then to remain almost constant throughout the rest of the reaction.

A digital correlator with blinker facility

Abstract: A digital correlator and probability analyser suitable for applications in photon correlation spectroscopy are described The correlator incorporates a device to minimise the effect of dust (the blinker) and enable light-scattering measurements to be made on less than scrupulously clean solutions The electronic circuits and their operation are described Experimental results are presented to show how the effect of dust contamination in a solution of polystyrene latex spheres can be minimised

Influence of double scattering in determination of rotational diffusion coefficients by depolarized dynamic light scattering: Application to the bacteriophages T7 and T4B

Abstract: Dynamic light scattering experiments were performed on solutions of the bacteriophages T7 and T4B in order to obtain the rotational diffusion coefficients of these phages. Correlation functions were determined from the depolarized intensity scattered in the forward direction. The apparatus used in this study is described in detail. Particular attention is paid to the minimalization of the depolarized intensity due to double scattering. If double scattering cannot be neglected, the correlation function of the depolarized field is the sum of the correlation functions resulting from single and double scattering. It is shown that by correcting for double scattering, it is then possible to obtain the rotational diffusion coefficient of the macromolecules. Although the optical anisotropy of both T4B (retracted fibers) and T7 is very small, the experimental conditions could be chosen in such a way that no depolarized scattering due to double scattering was observed. The measured rotational diffusion coefficients for T4B and T7 are D = 258 ± 12 and 4528 ± 100 sec−1, respectively. These values compare very well with those obtained by electric birefringence experiments.

Light scattering studies on solutions containing calcium phosphates

Abstract: A number of light scattering experiments was performed on calcium and phosphate containing solutions at pH 8.33 and 26°C. Supplementary information was obtained by means of dynamic light scattering, scanning electron microscopy, and transmission electron microscopy. The measurements prove that during the period in which amorphous calcium phosphate is present, coagulation is the dominant process that gives rise to the observed changes in the scattering intensity.

A study of the emulsifier-free polymerization of styrene by laser light-scattering techniques

Abstract: Conventional and dynamic light-scattering techniques have been used in conjunction with transmission electron microscopy and gas—liquid chromatography to study the persulfate-initiated polymerization of styrene in aqueous solution. The aim was to determine whether light scattering could produce information on this system, not easily obtained in other ways, which could be useful in understanding the earliest stages of particle growth and nucleation. Gas—liquid chromatography (glc) techniques indicated that the concentration of styrene in the system examined was relatively low, however, it appeared sufficient to support nucleation and growth processes similar to those found to occur during the initial stages of emulsion polymerization in the usual stirred reactions. Mean intensity light scattering showed that the reactions could be divided into two stages; an induction period, A, followed by a period of particle growth which continued until the reaction had stopped, B. Photon correlation spectroscopy (PCS) was used to determine the particle sizes during interval B and was found to give data in reasonable agreement to those obtained by TEM examination of samples removed from identical reactions. PCS data were distorted during the early stages of interval B by number density fluctuations. The particle number density appeared to increase as the reaction proceeded, eventually reaching a level where fluctuations in the number of particles in the sampling volume became unobservable using PCS. However, plots of the mean intensity of light scattered and particle diameter versus time indicated that the number density continued to increase throughout interval B. EM data showed that the number density of the particles decreased during the early stages and that as the reaction proceeded the standard deviation of the particle size distribution became less, indicating that the apparent increase in number density observed arose from the dependence of light scattering on the sixth power of the particle diameter.

Light Scattering from Sterically Stabilized Silica Particles

Abstract: During the last few years there has been considerable interest in the study of the dynamic properties of colloidal systems. This is mainly due to the development of the photon correlation spectroscopy, which makes it possible to study the Brownian motion of colloidal dispersions by measuring the particle diffusion coefficient. This experimental technique also stimulated much theoretical work on the influence of the interparticle interactions on the Brownian motion (1–14). The existing theories contain explicit results for the concentration dependence of the diffusion coefficient for interacting hard spheres in diluted systems, in the long wavelength limit.

The Application of dynamic light scattering and fluorescence depolarization to the determination of macromolecular binding characteristics

Abstract: Dynamic light scattering and fluorescence depolarization, two methods sensitive to the hydrodynamic parameters of molecules, are applied to the study of the following reactions: binding of hormone-substituted TMV to membrane vesicles, binding of ACTH to G6PDH, binding of dansyl-labelled H-Ala-Ala-Phe-OH to a-chymotrypsin and binding of NADH to LDH. Experimental con¬ ditions that have to be fulfilled for an accurate and meaning¬ ful determination of the binding parameters are given and the limitations of the methods are discussed. The instrumentation that had to be developped is described in some detail and some aspects of the data analysis are treated.

Dynamic Light Scattering from Thin, Free, Liquid Films

Abstract: Light scattering techniques have proven to be a powerful tool in studying physicochemical properties of thin, free, liquid films. Both, time averaged (1,2) and dynamic (3,4,5,6) light scattering experiments have been carried out on such systems.

Influence of chain conformation on translational diffusion of poly(2-vinyl pyridine) in dilute solution

Abstract: A comparative photon correlation spectroscopy study is reported of the concentration-dependent translational diffusion coefficient Dt of atactic poly(2-vinyl pyridine) in tetrahydrofuran and in aqueous solution, in the form of the poly(2-vinyl pyridinium)chloride salt (α = 0.4). The limiting Stokes radius of the polymer is observed to be identical within experimental error in tetrahydrofuran (THF) at temperatures below 30°C and in aqueous solutions at high ionic strength. This numerical value is comparable to expectation for an unperturbed atactic vinyl polymer chain and indicates a compact, possibly micellar, conformation. Raising the temperature in THF above 30°C and decreasing the ionic strength or increasing the ionization above α = 0.4 in aqueous solvents causes a discontinuous cooperative transition to a more expanded structure. The effect of the conformational change is also manifest in the concentration dependence of Dt. Using experimental estimates of the second osmotic virial coefficients obtained by total scattered intensity measurements, the experimental data for dDt/dc are compared with prediction based on hydrodynamic theory. Substantial disagreement is found between theory and experiment, especially in the aqueous system. In 0.01M NaCl, decrease in polyion concentration induces the transition from the compact form to a highly extended structure. Angle-dependent quasielastic light scattering data from the expanded state provides information about the intramolecular chain dynamics.

Dynamic light scattering in a flow—a new method of particle anisotropy investigation

Abstract: This paper deals with the light scattering from particles rotating in a flow with a transverse velocity gradient. It is theoretically substantiated and experimentally proved that the scattered light spectrum contains reliable information of the particle configuration and dimensions. The proposed technique may prove also very promising for the analysis of particle polydispersion.