In this joint experimental-theoretical work we study hydrodynamic interaction effects in dense suspensions of charged colloidal spheres. Using x-ray photon correlation spectroscopy we have determined the hydrodynamic function $H(q)$, for a varying range of electrosteric repulsion. We show that $H(q)$ can be quantitatively described by means of a novel Stokesian dynamics simulation method for charged Brownian spheres, and by a modification of a many-body theory developed originally by Beenakker and Mazur. Very importantly, we can explain the behavior of $H(q)$ for strongly correlated particles without resorting to the controversial concept of hydrodynamic screening, as was attempted in earlier work by Riese et al. [Phys. Rev. Lett. 85, 5460 (2000)].
We present a scaling formula for size-dependent viscosity coefficients for proteins, polymers, and fluorescent dyes diffusing in complex liquids. The formula was used to analyze the mobilities of probes of different sizes in HeLa and Swiss 3T3 mammalian cells. This analysis unveils in the cytoplasm two length scales: (i) the correlation length ξ (approximately 5 nm in HeLa and 7 nm in Swiss 3T3 cells) and (ii) the limiting length scale that marks the crossover between nano- and macroscale viscosity (approximately 86 nm in HeLa and 30 nm in Swiss 3T3 cells). During motion, probes smaller than ξ experienced matrix viscosity: η(matrix) ≈ 2.0 mPa·s for HeLa and 0.88 mPa·s for Swiss 3T3 cells. Probes much larger than the limiting length scale experienced macroscopic viscosity, η(macro) ≈ 4.4 × 10(-2) and 2.4 × 10(-2) Pa·s for HeLa and Swiss 3T3 cells, respectively. Our results are persistent for the lengths scales from 0.14 nm to a few hundred nanometers.
The effect of different ions on the formation and behavior of quadruplex structures of the human telomere sequence d(TTAGGG)4 has been studied by photon correlation spectroscopy (PCS) and circular dichroism (CD). The saturation and melting curves obtained in the presence of K+, Na+, Rb+, Li+, Cs+, and Sr2+ ions were recorded by CD spectroscopy and indicated the formation of monomeric quadruplexes. Analysis of the saturation curves obtained at 2 °C has shown that the presence of a single Sr2+ ion per oligomer is sufficient for the formation of a monomeric quadruplex of the DNA sequence studied. In the presence of SrCl2 at a concentration of 50 mM, the formation of tetrameric quadruplexes has been detected. The effect of Sr2+ ions on the formation of quadruplex structures by the human telomere sequence d(TTAGGG)4 is stronger and different from that of the other ions tested. The paper also presents results of a study of electrostatic interactions in solution. The translation diffusion coefficients DT of the structures present in solution have been determined by photon correlation spectroscopy and the effective charges on the structures have been calculated by combining the experimental data with the results based on the coupled mode theory. Analysis of the melting points monitored by the CD method has permitted a determination of Δn, the number of ions released in the process of thermal denaturation. All the results are in good agreement with the predictions based on the theory of polyelectrolytes. The effect of ions on the formation and behavior of quadruplex structures of the human telomere sequence d(TTAGGG)4 has been studied by photon correlation spectroscopy and circular dichroism.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The effect of intramolecular relaxations on the damping of longitudinal and transverse phonons was studied in poly(methylphenylsiloxane) (PMPS) and poly(ethylmethylsiloxane) (PEMS) polymers by means of Brillouin spectroscopy. It is shown that studies of the polarized and depolarized Brillouin spectra as functions of temperature and pressure allow for the separation of the contributions of the internal and structural relaxations to the damping of longitudinal and transverse phonons, respectively. In polymers with intramolecular relaxations these processes contribute not only to the damping of longitudinal phonons, according to theoretical predictions, but also transverse phonons, in contradiction to the theory.
The authors present a joint experimental-theoretical study of collective diffusion properties in aqueous suspensions of charge-stabilized fluorinated latex spheres. Small-angle x-ray scattering and x-ray photon correlation spectroscopy have been used to explore the concentration and ionic-strength dependence of the static and short-time dynamic properties including the hydrodynamic function H(q), the wave-number-dependent collective diffusion coefficient D(q), and the intermediate scattering function over the entire accessible range. They show that all experimental data can be quantitatively described and explained by means of a recently developed accelerated Stokesian dynamics simulation method, in combination with a modified hydrodynamic many-body theory. In particular, the behavior of H(q) for de-ionized and dense suspensions can be attributed to the influence of many-body hydrodynamics, without any need for postulating hydrodynamic screening to be present, as it was done in earlier work. Upper and lower boundaries are provided for the peak height of the hydrodynamic function and for the short-time self-diffusion coefficient over the entire range of added salt concentrations.
A speckle pattern can be observed in the polarized component of light scattered from glass forming liquids far above their glass transition temperature. This speckle pattern fluctuates with characteristic time that corresponds to the relaxation time of the additional ultraslow component in the correlation function and is about seven orders of magnitude longer than the relaxation time of the alpha-process. This slow process is out of the experimental time window when the alpha-process is measured by means of the photon correlation spectroscopy and results in an apparent nonergodicity which can be seen as a baseline offset in the ensemble-averaged correlation function. In contrast, the time-averaged field correlation functions which have been measured in practically all light scattering studies always decay to zero. The slow process contributes a q-dependent excess intensity to the polarized component of scattered light. The values of the nonergodicity parameters obtained from the static and dynamic light scattering experiments are equal. Both the slow component and the excess intensity result from denser regions of fractal character which develop in glass-forming liquids on approaching the glass transition.
ADVERTISEMENT RETURN TO ISSUEPREVArticleSeparation of two relaxation processes in bulk polymers using photon correlation spectroscopy at high pressuresG. Fytas, G. Meier, T. Dorfmueller, and Adam PatkowskiCite this: Macromolecules 1982, 15, 1, 214–216Publication Date (Print):January 1, 1982Publication History Published online1 May 2002Published inissue 1 January 1982https://pubs.acs.org/doi/10.1021/ma00229a045https://doi.org/10.1021/ma00229a045research-articleACS PublicationsRequest reuse permissionsArticle Views56Altmetric-Citations31LEARN 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 InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
A knee-shaped feature observed earlier in light scattering spectra of Ca0.4K0.3(NO3)1.4 (CKN) below Tc is used as a strong argument in favor of mode-coupling theory of the glass transition (MCT). Our careful measurements reveal no “knee” in the spectra of two glass forming liquids, CKN and ortho-terphenyl. Instead of the knee the spectra show nontrivial broadening and an increase of the intensity with a temperature increase. Both variations are confirmed by neutron scattering measurements on CKN and are neither expected in the asymptotic MCT predictions nor in any other model.
