Internal Structure Of Aggregates Research Articles

Extended x-ray absorption fine-structure studies of the internal aggregate structure in lightly sulfonated polystyrene. 2. Effect of uniaxial orientation

EXAFS spectra were measured for three uniaxally extended lightly sulfonated polystyrenes, each containing 6.1 mol % sulfonate groups. The X-rays were linearly polarized, which enabled changes in local structure to be monitored parallel and perpendicular to the stretch direction. For the zinc-neutralized material, the metal-oxygen first-shell distance increased parallel to the stretch direction. Also, the Zn-O first-shell bond vectors were aligned in the stretch direction. A simple theoretical description was developed which allowed quantification of the second moment of the orientation function for these bond vectors. In the nickel-neutralized material, the metal-oxygen first-shell distance did not increase, but Ni-O bond vectors also aligned in the stretch direction

Extended x-ray absorption fine-structure studies of the internal aggregate structure in lightly sulfonated polystyrene. 1. Determination of the coordination environment about the cation

Three lightly sulfonated polystyrenes containing 6.1 mol % sulfonate groups neutralized with Ni 2+ , Cd 2+ , and Zn 2+ were studied with the EXAFS technique. Using the simulation package FEFF5, it was found that the atomic arrangement whichled to the best description of the experimental data was very similar for the nickel- and zinc-neutralized materials. Nickel was octahedrally coordinated to oxygen in the first shell, while zinc was tetrahedrally coordinated to oxygen. In both cases, the second shell was sulfur atoms with a metal-oxygen-sulfur angle of 135-140 o

ON THE MICRORHEOLOGICAL MODELING OF AGGREGATING COLLOIDS

ABSTRACT Microrheological modeling of the aggregating colloidal dispersions in frames of the mean-field approach Is used to relate their Theological behavior to the parameters of the aggregates. Three parameters are shown to form a minimum set of values which one should know to elaborate the simplest self-consistent microrheological model of aggregating colloids. They are: the yield strength of the compact structure o, fractal dimension D and the exponent m, which characterizes the dependence of the aggregates radius R vs shear rate S (R ∝ S−m). Analytic consideration and computer simulations are carried out to determine the exponent m for the aggregates of different type. The behavior of the aggregate depends on the character of the particles Interaction. In general the interaction force can be considered a superposition of central component (equivalent to ordinary spring) and some non-central component. If the non-central Interaction Is relevant, the aggregate internal structure is rigid (I.e. it elasti...

On the model of colloid aggregates and aggregating colloids

Computer simulations were used to investigate the power law dependence of the elastic compression modulus and the yield stress (∝R−γ) of two-dimensional (2D) and three-dimensional (3D) aggregates of special type (fractal trees without loops on square and simple cubic lattices) on the radius R of the aggregates. The elastic forces between particles were described by the Born model. Scaling exponent γ was found to be slightly dependent on the geometrical parameters of the aggregates internal structure and the parameters of interaction (it ranges in the limits 1.3–1.7 in 2D and 1.8–2.6 in 3D). If the interparticle forces are purely central, the internal structure of aggregates is not able to transmit any elastic stress. In this case simulations of the disaggregation process were carried out in 2D in free draining approximation. It was shown that the initial aggregate is broken into two or more secondary aggregates. The mean radius of these aggregates decreases as the shear rate increases. Relevance of these data for the microrheological models of aggregating colloids in shear flow is demonstrated. In terms of the mean field model, the viscosity of aggregating colloid is calculated as a function of shear rate. In this model aggregates are characterized by two exponents: fractal dimension and γ. The values of γ, which were obtained in our simulations, are found to be close to those values which are needed to find the best fit between the mean field model and the computer simulations data for aggregating colloids previously obtained by other authors.

Internal fractal structure of aggregates of silver particles and its consequences on surface-enhanced Raman scattering intensities

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInternal fractal structure of aggregates of silver particles and its consequences on surface-enhanced Raman scattering intensitiesO. Siiman and H. FeilchenfeldCite this: J. Phys. Chem. 1988, 92, 2, 453–464Publication Date (Print):January 1, 1988Publication History Published online1 May 2002Published inissue 1 January 1988https://doi.org/10.1021/j100313a042RIGHTS & PERMISSIONSArticle Views293Altmetric-Citations51LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (5 MB) Get e-Alerts

Internal structure of diffusion-limited aggregates.

Internal structure of diffusion-limited aggregates.

Internal structure of aggregates of two amphiphilic species in a lyotropic liquid crystal

The internal structure of a ribbon-like aggregate in an ordered mesophase with rectangular symmetry formed by two amphiphiles, sodium decyl sulfate and decanol, in presence of water, is investigated by neutron scattering. Our results show that the two amphiphiles are not uniformly distributed within the aggregate. Their relative concentration is modulated according to the local interfacial curvature of the aggregate. Such a concentration/curvature relationship may be an important point to understand the shape of the aggregates and therefore the polymorphism of lyotropic liquid crystals Etude par diffusion de neutrons de la structure interne d'un agregat en forme de ruban dans une mesophase ordonnee a symetrie rectangulaire formee par deux amphiphiles, decylsulfate de sodium et decanol, en presence d'eau. Distribution non uniforme des deux amphiphiles dans l'agregat, leur concentration relative variant localement selon la courbure interfaciale de l'agregat

Internal Structure and Development Processes of C-Scale Aggregates of Cumulus Clouds

Abstract Law echoes (C-scale in GATE terminology., approximately 100 to 10 000 km2) seem to produce most of the precipitation that occurs in tropical systems. These large echoes are seen to last several hours and comprise many smaller and short-lived cells that grow and die within their bounds or are merged with them. In this paper, quantitative GATE radar data are used to statistically characterize these composite echoes as a whole, and to study their internal structure, formation and development processes. In addition, statistics of the individual cells making up the composite echoes are presented. These are compared to similar data for cells that develop individually away from the aggregates. In this way, some information is obtained about the duration, rain-producing ability and the size of those cells that merge to form larger groups compared to those clouds that form, develop and die relatively independently of one another.

Rotation-mediated histogenetic aggregation of dissociated cells: A quantifiable approach to cell interactions in vitro

1. 1. This report examines the possibility of compounding cells in suspension into histoformative aggregates, under controllable, replicable and potentially quantitative conditions. 2. 2. A cell aggregation procedure based on readily standardizable manipulations is described, whereby cells dissociated enzymatically from embryonic tissues may be aggregated in various combinations and concentrations into developmentally effective multicellular structures; it is suitable for analyzing mutual reactions of cells and their responses to diverse environmental conditions. 3. 3. The characteristics of aggregates produced by cells of different types or origins varied markedly under otherwise identical conditions. The number, size distribution, shape and internal structure of aggregates formed in 24 hours by cells of a given type or by a cell population of a known composition was termed the aggregation pattern of the cells in testing (cell type-dependent aggregation pattern) for the specified set of conditions. 4. 4. Aggregation patterns of the two types of cells studied were not noticeably affected by gross variations in cell concentrations. It is suggested that they represent a typical, reproducible and measurable expression of cell behavior, providing useful “baselines” for further analysis. For comparative purposes, they may be conveniently expressed as the ratio between average diameter and number of aggregates, which provides an index of aggregation for the given culture and conditions. 5. 5. The histoformative effectiveness of this procedure was established by studying the differentiation of aggregates. In all experiments the re-assembled cells resumed development in accordance with their pre-established directions. 6. 6. Type-specific grouping of cells in heterotypic cell aggregates, compounded by the present procedure, was examined in combinations of embryonic chick and mouse cells. In spite of their initial random bunching and irrespective of species origin, the aggregated cells became sorted out and associated in accordance with their histogenetic identities and compatibilities, thus confirming prior findings on “self-assembled” aggregates. 7. 7. The size distribution of aggregates could be effectively controlled by varying the frequency of rotation of cultures. The possibility of a measurable relationship between the forces applied to cells and cell cohesiveness is discussed. 8. 8. The rate and effectiveness of aggregation processes in this system was found to decrease at suboptimal temperatures. At 15 °C, the two types of cells examined showed no aggregation; transferred to 38 °, these cells aggregated readily. The possibility is considered that normal bonding and formative association of cells depend on thermo-sensitive synthetic activities, related, perhaps, to elaboration of surface products, and that their rate is slowed down or otherwise modified at suboptimal temperatures.