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Poly(ethylene oxide)-sodium dodecyl sulfate interactions studied using static and dynamic light scattering

Brown, Wyn; Fundin, Johan; Miguel, Maria da Graça
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
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Static and dynamic light scattering measurements have been made on poly(ethy1ene oxide) (PEO) in the presence of the ionic surfactant sodium dodecyl sulfate (SDS) in aqueous solution over a range of relative concentrations. The purpose was, in part, to demonstrate the polyelectrolyte effecte which arise in PEO on formation of the charged complex between the components in solution in which small SDS micelles are incorporated into the flexible PEO coil. The influence of the ionic strength of the medium was studied. Static light scattering measurements show that the radius of gyration changes as a function of SDS concentration and the ionic strength of the medium. Diffusion coefficients from dynamic light scattering (DLS) reflect changes in the pair interaction potential as the SDS and ionic strength are altered. Laplace inversion of the DLS time correlation function gives relaxation time distributions consisting of the PEO/SDS complex as the main component and free SDS micelles as the minor component. Changes in peak areas are related to the increase in the degree of binding between SDS and PEO as the relative concentrations change and also the increase in SDS micellar size with increase in the ionic strength of the medium.; http://dx.doi.org/10.1021/ma00052a019

Dynamic light scattering and optical absorption spectroscopy study of pH and temperature stabilities of the extracellular hemoglobin of Glossoscolex paulistus

SANTIAGO, Patricia S.; MOURA, Franciane; MOREIRA, Leonardo M.; DOMINGUES, Marco M.; SANTOS, Nuno C.; TABAK, Marcel
Fonte: BIOPHYSICAL SOC Publicador: BIOPHYSICAL SOC
Tipo: Artigo de Revista Científica
ENG
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The extracellular hemoglobin of Glossoscolex paulistus (HbGp) is constituted of subunits containing heme groups, monomers and trimers, and nonheme structures, called linkers, and the whole protein has a minimum molecular mass near 3.1 x 10(6) Da. This and other proteins of the same family are useful model systems for developing blood substitutes due to their extracellular nature, large size, and resistance to oxidation. HbGp samples were studied by dynamic light scattering (DLS). In the pH range 6.0-8.0, HbGp is stable and has a monodisperse size distribution with a z-average hydrodynamic diameter (D-h) of 27 +/- 1 nm. A more alkaline pH induced an irreversible dissociation process, resulting in a smaller D-h of 10 +/- 1 nm. The decrease in D-h suggests a complete hemoglobin dissociation. Gel filtration chromatography was used to show unequivocally the oligomeric dissociation observed at alkaline pH. At pH 9.0, the dissociation kinetics is slow, taking a minimum of 24 h to be completed. Dissociation rate constants progressively increase at higher pH, becoming, at pH 10.5, not detectable by DILS. Protein temperature stability was also pH-dependent. Melting curves for HbGp showed oligomeric dissociation and protein denaturation as a function of pH. Dissociation temperatures were lower at higher pH. Kinetic studies were also performed using ultraviolet-visible absorption at the Soret band. Optical absorption monitors the hemoglobin autoxidation while DLS gives information regarding particle size changes in the process of protein dissociation. Absorption was analyzed at different pH values in the range 9.0-9.8 and at two temperatures...

What can light scattering spectroscopy do for membrane-active peptide studies

DOMINGUES, Marco M.; SANTIAGO, Patricia S.; CASTANHO, Miguel A. R. B.; SANTOS, Nuno C.
Fonte: JOHN WILEY & SONS LTD Publicador: JOHN WILEY & SONS LTD
Tipo: Artigo de Revista Científica
ENG
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902.7043%
Highly charged peptides are important components of the immune system and belong to an important family of antibiotics. Although their therapeutic activity is known, most of the molecular level mechanisms are controversial. A wide variety of different approaches are usually applied to understand their mechanisms, but light scattering techniques are frequently overlooked. Yet, light scattering is a noninvasive technique that allows insights both on the peptide mechanism of action as well as on the development of new antibiotics. Dynamic light scattering (DLS) and static light scattering (SLS) are used to measure the aggregation process of lipid vesicles upon addition of peptides and molecular properties (shape, molecular weight). The high charge of these peptides allows electrostatic attraction toward charged lipid vesicles, which is studied by zeta potential (zeta-potential) measurements. Copyright (c) 2008 European Peptide Society and John Wiley & Sons, Ltd.

Light scattering on the structural characterization of DMPG vesicles along the bilayer anomalous phase transition

Enoki, Thais Azevedo; Henriques, Vera Bohomoletz; Lamy, Maria Teresa Moura
Fonte: ELSEVIER IRELAND LTD; CLARE Publicador: ELSEVIER IRELAND LTD; CLARE
Tipo: Artigo de Revista Científica
ENG
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896.79086%
Highly charged vesicles of the saturated anionic lipid dimyristoyl phosphatidylglycerol (DMPG) in low ionic strength medium exhibit a very peculiar thermo-structural behavior. Along a wide gel-fluid transition region, DMPG dispersions display several anomalous characteristics, like low turbidity, high electrical conductivity and viscosity. Here, static and dynamic light scattering (SLS and DLS) were used to characterize DMPG vesicles at different temperatures. Similar experiments were performed with the largely studied zwitterionic lipid dimyristoyl phosphatidylcholine (DMPC). SLS and DLS data yielded similar dimensions for DMPC vesicles at all studied temperatures. However, for DMPG, along the gel-fluid transition region, SLS indicated a threefold increase in the vesicle radius of gyration, whereas the hydrodynamic radius, as obtained from DLS, increased 30% only. Despite the anomalous increase in the radius of gyration, DMPG lipid vesicles maintain isotropy, since no light depolarization was detected. Hence, SLS data are interpreted regarding the presence of isotropic vesicles within the DMPG anomalous transition, but highly perforated vesicles, with large holes. DLS/SLS discrepancy along the DMPG transition region is discussed in terms of the interpretation of the Einstein-Stokes relation for porous vesicles. Therefore...

Sodium dodecyl sulfate (SDS) effect on the thermal stability of oxy-HbGp: Dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) studies

Carvalho, José Wilson P.; Alves, Fernanda Rosa; Batista, Tatiana; Carvalho, Francisco Adriano O.; Santiago, Patrícia S.; Tabak, Marcel
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 561-570
ENG
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Glossoscolex paulistus (HbGp) hemoglobin is an oligomeric protein, presenting a quaternary structure constituted by 144 globin and 36 non-globin chains (named linkers) with a total molecular mass of 3.6MDa. SDS effects on the oxy-HbGp thermal stability were studied, by DLS and SAXS, at pH 5.0, 7.0 and 9.0. DLS and SAXS data show that the SDS-oxy-HbGp interactions induce a significant decrease of the protein thermal stability, with the formation of larger aggregates, at pH 5.0. At pH 7.0, oxy-HbGp undergoes complete oligomeric dissociation, with increase of temperature, in the presence of SDS. Besides, oxy-HbGp 3.0mg/mL, pH 7.0, in the presence of SDS, has the oligomeric dissociation process reduced as compared to 0.5mg/mL of protein. At pH 9.0, oxy-HbGp starts to dissociate at 20°C, and the protein is totally dissociated at 50°C. The thermal dissociation kinetic data show that oxy-HbGp oligomeric dissociation at pH 7.0, in the presence of SDS, is strongly dependent on the protein concentration. At 0.5mg/mL of protein, the oligomeric dissociation is complete and fast at 40 and 42°C, with kinetic constants of (2.1±0.2)×10-4 and (5.5±0.4)×10-4s-1, respectively, at 0.6mmol/L SDS. However, at 3.0mg/mL, the oligomeric dissociation process starts at 46°C...

Dynamic light scattering and viscosimetry of aqueous solutions of pectin, sodium alginate and their mixtures: effects of added salt, concentration, counterions, temperature and chelating agent

Lima,Aline M. F.; Soldi,Valdir; Borsali,Redouane
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 EN
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The effects of added salt, concentration, counterions, temperature and chelating agent on aqueous solutions of pectin, sodium alginate and their mixtures were analyzed by viscosimetry and dynamic light scattering (DLS) techniques. The intrinsic viscosity of the binary systems decreased with the addition of salt and with temperature, while it was found to be insensitive to the addition of NaEDTA. As expected the intrinsic viscosity of the ternary alginate/pectin/water system was equal to the average of the intrinsic viscosity for the binary systems. The DLS studies indicated a bimodal distribution (fast and slow relaxation modes) for both binary and ternary systems at 25 °C, reflecting aggregation. A significant increase in the hydrodynamic radius, in the case of the slow mode, was observed for the binary and ternary systems in the presence of NaCl and KCl at 25 °C. However, at 80 °C the hydrodynamic radius for the slow mode in KCl solutions was practically constant for all the studied systems, except for the alginate binary solutions in which were not observed.

Dynamic light scattering from polydisperse suspensions of thin ellipsoidal shells of revolution with submicron diameters.

Fujime, S; Takasaki-Ohsita, M; Miyamoto, S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1988 EN
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Osmotic swelling of membrane vesicles has been studied in combination with dynamic light scattering, to obtain information about the elastic properties of biomembranes. In such studies, there arise some technical problems specific to dynamic light scattering, which include the effects on the light-scattering results of the size distribution and nonsphericity of the vesicles with submicron sizes. Even for highly monodisperse suspensions of spherical vesicles (sigma/dn = [(the mean of d2)/d2n-1]1/2 = 0.1; dn being the number-average diameter of vesicles), the average diameter d obtained from dynamic light scattering is shown to be strongly dependent on dnK, where K is the length of the scattering vector. This is solely due to the shell structure of the vesicles. For ellipsoidal vesicles, another complication appears which is due to the rotational motion of ellipsoids.

Static and dynamic light scattering of healthy and malaria-parasite invaded red blood cells

Park, YongKeun; Diez-Silva, Monica; Fu, Dan; Popescu, Gabriel; Choi, Wonshik; Barman, Ishan; Suresh, Subra; Feld, Michael S.
Fonte: Society of Photo-Optical Instrumentation Engineers Publicador: Society of Photo-Optical Instrumentation Engineers
Tipo: Artigo de Revista Científica
EN
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We present the light scattering of individual Plasmodium falciparum-parasitized human red blood cells (Pf-RBCs), and demonstrate progressive alterations to the scattering signal arising from the development of malaria-inducing parasites. By selectively imaging the electric fields using quantitative phase microscopy and a Fourier transform light scattering technique, we calculate the light scattering maps of individual Pf-RBCs. We show that the onset and progression of pathological states of the Pf-RBCs can be clearly identified by the static scattering maps. Progressive changes to the biophysical properties of the Pf-RBC membrane are captured from dynamic light scattering.

Anisotropic light scattering of individual sickle red blood cells

Kim, Youngchan; Higgins, John Matthew; Dasari, Ramachandra R.; Suresh, Subra; Park, YongKeun
Fonte: Society of Photo-Optical Instrumentation Engineers Publicador: Society of Photo-Optical Instrumentation Engineers
Tipo: Artigo de Revista Científica
EN_US
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702.7043%
Abstract. We present the anisotropic light scattering of individual red blood cells (RBCs) from a patient with sickle cell disease (SCD). To measure light scattering spectra along two independent axes of elongated-shaped sickle RBCs with arbitrary orientation, we introduce the anisotropic Fourier transform light scattering (aFTLS) technique and measured both the static and dynamic anisotropic light scattering. We observed strong anisotropy in light scattering patterns of elongated-shaped sickle RBCs along its major axes using static aFTLS. Dynamic aFTLS analysis reveals the significantly altered biophysical properties in individual sickle RBCs. These results provide evidence that effective viscosity and elasticity of sickle RBCs are significantly different from those of the healthy RBCs.

Association Behavior of Poly(methacrylic acid)-block-Poly(methyl methacrylate) in Aqueous Medium: Potentiometric and Laser Light Scattering Studies

Palaniswamy, R.; Wang, C; Tam, Michael K. C.; Gan, L.H.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 351681 bytes; application/pdf
EN_US
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Atom transfer radical polymerisation (ATRP) technique was used to synthesize poly(methacrylic acid-block-methyl methacrylate) (P(MAA₁₀₂-b-MMA₁₀)) copolymer in order to study the aggregation behavior in aqueous solution over the course of neutralization. A combination of static and dynamic light scattering (SLS, DLS) and potentiometric titration techniques were used to investigate the size and shape of the micelle at various degrees of neutralization. The hydrodynamic radius (Rh) determined from dynamic light scattering increases from ~26nm (for unneutralized) to ~42nm (for completely neutralized sample). Both potentiometric and laser light scattering studies indicate the formation of a core shell micelle. The weighted average molecular weights of the polymer and micelle are 1.18x10⁴ and 2.25 x 10⁵ g/mol respectively, which suggests that the aggregation number of the micelle is ~20.; Singapore-MIT Alliance (SMA)

Dynamic light scattering of semidilute hydrophobically modified alkali-soluble emulsion solutions with different lengths of poly(ethylene oxide) spacer chain

Dai, S.; Tam, K.; Jenkins, R.
Fonte: John Wiley & Sons Inc Publicador: John Wiley & Sons Inc
Tipo: Artigo de Revista Científica
Publicado em //2005 EN
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Semidilute solutions of hydrophobically modified alkali-soluble emulsion (HASE) were examined by dynamic light scattering and rheological techniques. For the model polymer without associative macromonomer, two q2 dependent diffusional modes were detected in the decay time distributions. With increasing hydrophobicity of the associative macromonomer, the narrow fast peak was substituted by a shallow broad peak and only one q2 dependent slow mode could be accurately detected, which indicated that the heterogeneity of these associated clusters increases with increasing carbon number. The bulk steady-shear viscosity exhibits similar results to the diffusion coefficients of the aggregate observed from light scattering measurements. The length of poly(ethylene oxide) (PEO) spacer chain alters the solution properties as well as the associative cluster structure. With increasing length of PEO spacer chain, intramolecular association was substituted by intermolecular association. For EO segment larger than 32 units, intramolecular association dominates, where the formation of HASE aggregates is controlled by the balance of electrostatic repulsion and hydrophobic attraction.; Sheng Dai, Kam Chiu Tam and Richard D. Jenkins

基于奇异值分解的动态光散射反演算法; An inversion algorithm of dynamic light scattering based on singular value decomposition

Yu, X.F.; Yang, H.; Yang, H.M.; Zheng, G.; Li, J.; Hu, H.Q.; Biggs, M.
Fonte: Kexue Chubanshe Publicador: Kexue Chubanshe
Tipo: Artigo de Revista Científica
Publicado em //2013 ZH
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针对动态光散射颗粒测量法在反演多分散系粒径分布时,算法需要先验信息或者解的约束条件的问题,提出了一种基于奇异值分解的动态光散射反演算法.首先利用多分散颗粒系光强自相关函数构造Hankel矩阵;其次对矩阵进行奇异值分解;再次根据奇异值的大小分布,确定噪音级别,重建矩阵的秩;最后对新的矩阵进行特征值分解,得到颗粒的粒径分布.采样两种和三种不同粒径的颗粒系进行了实验,结果显示:在没有任何先验信息和对解的约束条件下,该方法对两种粒径的颗粒系测量取得了较好的效果.但对于三种粒径的颗粒系测量效果并不理想,虽然能分辨出不同的三种粒径,但测量结果偏差较大,特别是小颗粒的粒径.通过分析认为主要原因是小颗粒的散射光容易被大颗粒阻挡.; YU Xiang-fei, YANG Hui, YANG Hai-ma, ZHENG Gang, LI Jun, HU Heng-qing, Mark BIGGS; English Title: An inversion algorithm of dynamic light scattering based on singular value decomposition. English Abstract: To solve the problem that the traditional inversion of dispersion particle size distribution with the method of dynamic light scattering requires prior knowledge or constraints for the solution...

Comparison of Dynamic Light Scattering and Centrifugal Sedimentation for Nanoparticle Sizing

COUTEAU OLIVIER; ROEBBEN GERT
Fonte: OPOCE Publicador: OPOCE
Tipo: Contributions to Conferences Formato: Printed
ENG
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701.86695%
To support the efforts of increasing confidence in the comparability of measurements in the field of nanotechnology, the Institute of Reference Materials and Measurements (IRMM) intends to produce reference materials with certified particle size in the nanometer range. Several techniques, which are based on different physical principles, have been developed to perform nanoparticle sizing. As a starting point in the certification of nanoparticle reference materials, IRMM is evaluating the differences between results obtained with two of the most commonly used nanoparticle sizing techniques: dynamic light scattering (DLS) and centrifugal sedimentation. The main difference between these techniques is their power to resolve multi-modal particle size distributions. Due to the separation process occurring in the disc centrifuge, centrifugal sedimentation has an excellent resolution and is able to resolve modes with a diameter ratio as low as 1.1 whereas dynamic light scattering is not able to resolve modes with a diameter lower than 4. However, dynamic light scattering is based on first principles and calibration is not needed as for centrifugal sedimentation, for which the sedimentation velocity must be calibrated. This paper will present experimental results...

Comparison between Centrifugal Sedimentation and Dynamic Light Scattering for Nanoparticle Sizing

COUTEAU OLIVIER; ROEBBEN GERT
Fonte: Institute of Particle Technology Publicador: Institute of Particle Technology
Tipo: Contributions to Conferences Formato: CD-ROM
ENG
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701.86695%
The Institute for Reference Materials and Measurements (IRMM) has produced and distributes a series of reference materials with certified particle size. IRMM has the intention to broaden the range of these certified particle size reference materials to the nanoparticles range. To perform nanoparticle sizing, a variety of instruments exists, each based on different physical principles. The certification process has started with an evaluation of two of the most common nanoparticle sizing techniques: centrifugal sedimentation and dynamic light scattering. The main difference between these techniques is the resolution for multi-modal particle size distributions. due to the separation process occurring in the disc centrifuge, centrifugal sedimentation has an excellent resolution and is able to resolve modes with a diameter rratio as low as 1.1 whereas dynamic light scattering is not able to resolve modes with a diameter ratio lower than 4. However, dynamic light scattering is based on first principles and calibration is not needed as for centrifugal sedimentation for which the sedimentation velocity must be calibrated. This paper will present the results of the comparison tests, illustrating the advantages and drawbacks associated with each technique and it will show how these two techniques can complement each other in the certification process.; JRC.D.2-Reference materials

Systematic analysis of protein-detergent complexes applying dynamic light scattering to optimize solutions for crystallization trials

Meyer, Arne; Dierks, Karsten; Hussein, Rana; Brillet, Karl; Brognaro, Hevila; Betzel, Christian
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica Formato: 75-81
ENG
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Detergents are widely used for the isolation and solubilization of membrane proteins to support crystallization and structure determination. Detergents are amphiphilic molecules that form micelles once the characteristic critical micelle concentration (CMC) is achieved and can solubilize membrane proteins by the formation of micelles around them. The results are presented of a study of micelle formation observed by in situ dynamic light-scattering (DLS) analyses performed on selected detergent solutions using a newly designed advanced hardware device. DLS was initially applied in situ to detergent samples with a total volume of approximately 2 mu l. When measured with DLS, pure detergents show a monodisperse radial distribution in water at concentrations exceeding the CMC. A series of all-transn-alkyl--D-maltopyranosides, from n-hexyl to n-tetradecyl, were used in the investigations. The results obtained verify that the application of DLS in situ is capable of distinguishing differences in the hydrodynamic radii of micelles formed by detergents differing in length by only a single CH2 group in their aliphatic tails. Subsequently, DLS was applied to investigate the distribution of hydrodynamic radii of membrane proteins and selected water-insoluble proteins in presence of detergent micelles. The results confirm that stable protein-detergent complexes were prepared for (i) bacteriorhodopsin and (ii) FetA in complex with a ligand as examples of transmembrane proteins. A fusion of maltose-binding protein and the Duck hepatitis B virus X protein was added to this investigation as an example of a non-membrane-associated protein with low water solubility. The increased solubility of this protein in the presence of detergent could be monitored...

A ‘Universal’ Bottom-up Sol-gel Based Synthesis of Pzt (1-x)/x Submicrometric Structures: 1. Dynamic Light Scattering Characterization of Precursor Stability and Aggregation Kinetics

Suárez-Gómez,Amaury; Rodríguez-Iglesias,Vladimir
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2015 EN
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This work proposes an extension of a sol-gel based synthesis route for obtaining highly hydrophobic, uniformly nanosized and stable precursor solutions of lead zirconate titanate [Pb(Zr1-xTix)O3 or PZT (1-x)/x] for any given (1-x)/x Zr:Ti ratio. Several representative PZT compositions were chosen and their precursors were studied by taking into account the time dependence of the mean particles size andthe predominant aggregation kinetics. Size distributions were recorded by the Dynamic Light Scattering technique and the aggregation kinetics was explored by considering a Diffusion-Limited Colloidal Aggregation model. Transmission electron microscopy was also used to characterize some morphological features of our resultant precursor nanoparticles. Our final results supports the universalization of this approach to any PZT composition and its extension to other material systems. This work is intended to be the first on a series dealing with the sol-gel based synthesis of any PZT material at any scale using a bottom-up approach.

Investigating Static and Dynamic Light Scattering

Sun, Yong
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/10/2011
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A new size, static radii $R_{s}$, can be measured accurately using Static Light Scattering (SLS) technique when the Rayleigh-Gans-Debye approximation is valid for dilute homogenous spherical particles in dispersion. The method proposed in this work not only can measures the particle size distribution and average molar mass accurately but also enables us to explore Dynamic Light Scattering (DLS) technique further. Detailed investigation of the normalized time auto-correlation function of the scattered light intensity $g^{2)}(\tau)$ shows that the measurements of DLS can be expected accurately and the static and hydrodynamic radii of nanoparticles are different. Only at some special conditions, the Z-average hydrodynamic radius can be measured accurately at a given scattering angle. The fact that the values of average hydrodynamic radius measured at different scattering angles are consistent or the values of polydispersity index are small does not mean the particle size distribution is narrow or monodisperse.; Comment: 8 figures, discussing the questions about the accurate size measurements of particles obtained using Dynamic Light Scattering technique and the particle sizes obtained using Static Light Scattering technique

Measurement of Dynamic Light Scattering Intensity in Gels

Rochas, Cyrille; Geissler, Erik
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/03/2015
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In the scientific literature little attention has been given to the use of dynamic light scattering (DLS) as a tool for extracting the thermodynamic information contained in the absolute intensity of light scattered by gels. In this article we show that DLS yields reliable measurements of the intensity of light scattered by the thermodynamic fluctuations, not only in aqueous polymer solutions, but also in hydrogels. In hydrogels, light scattered by osmotic fluctuations is heterodyned by that from static or slowly varying inhomogeneities. The two components are separable owing to their different time scales, giving good experimental agreement with macroscopic measurements of the osmotic pressure. DLS measurements in gels are, however, tributary to depolarised light scattering from the network as well as to multiple light scattering. The paper examines these effects, as well as the instrumental corrections required to determine the osmotic modulus. For guest polymers trapped in a hydrogel the measured intensity, extrapolated to zero concentration, is identical to that found by static light scattering from the same polymers in solution. The gel environment modifies the second and third virial coefficients, providing a means of evaluating the interaction between the polymers and the gel.

Multiple scattering suppression in dynamic light scattering based on a digital camera detection scheme

Zakharov, Pavel; Bhat, Suresh; Schurtenberger, Peter; Scheffold, Frank
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/05/2005
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We introduce a charge coupled device (CCD) camera based detection scheme in dynamic light scattering that provides information on the single-scattered auto-correlation function even for fairly turbid samples. It is based on the single focused laser beam geometry combined with the selective cross correlation analysis of the scattered light intensity. Using a CCD camera as a multispeckle detector we show how spatial correlations in the intensity pattern can be linked to single and multiple scattering processes. Multiple scattering suppression is then achieved by an efficient cross correlation algorithm working in real time with a temporal resolution down to 0.2 seconds. Our approach allows access to the extensive range of systems that show low-order scattering by selective detection of the singly scattered light. Model experiments on slowly relaxing suspensions of titanium dioxide in glycerol were carried out to establish the validity range of our approach. Successful application of the method is demonstrated up to a scattering coefficient of more than $\mu_s = 5$ cm$^{-1}$ for the sample size of L=1 cm.; Comment: submitted to Applied Optics

Estimation of the particle size distribution of a dilute latex from combined elastic and dynamic light scattering measurements: A method based on neural networks

Stegmayer,G.S.; Gonzalez,V.D.; Gugliotta,L.M.; Chiotti,O.A.; Vega,J.R.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/07/2009 EN
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A method for estimating the particle size distribution (PSD) of a dilute latex from light scattering measurements is presented. The method utilizes a general regression neural network (GRNN), that estimates the PSD from 2 independent sets of measurements carried out at several angles: (i) light intensity measurements, by elastic light scattering (ELS); and (ii) average diameters measurements, by dynamic light scattering. The GRNN was trained with measurements simulated on the basis of typical asymmetric PSDs (unimodal normal-logarithmic distributions of variable mean diameters and variances). First, the ability of the method was tested on the basis of two synthetic examples. Then, the obtained GRNN was used for estimating the PSD of a narrow polystyrene (PS) latex standard of nominal diameter 111 nm. The standard was also characterized by 2 independent techniques: capillary hydrodynamic fractionation, and transmission electron microscopy (TEM). The PSD predicted by the GRNN resulted close to that obtained by TEM. The estimated PSDs were better than those obtained through standard numerical techniques for 'ill-conditioned' inverse problems.