Dynamics in dense suspensions of charge-stabilized colloidal particles

Robert, Aymeric; Wagner, Joachim; Härtl, W.; Autenrieth, Tina; Grübel, G.

doi:10.1140/epje/i2007-10265-5

Cited by 20 publications

(27 citation statements)

References 17 publications

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“…11,[17][18][19][20][21][22][23][24][25] In particular, no unusually small, so-called ultra slow values of H(Q m ), as reported in Ref. 72 in conflict with the theoretical predictions, have been found in our study.…”

Section: B Wavenumber Dependent Diffusion and Scaling Relationscontrasting

confidence: 56%

Structure and short-time dynamics in concentrated suspensions of charged colloids

Westermeier

Fischer

Roseker

et al. 2012

The Journal of Chemical Physics

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We report a comprehensive joint experimental-theoretical study of the equilibrium pair-structure and short-time diffusion in aqueous suspensions of highly charged poly-acrylate (PA) spheres in the colloidal fluid phase. Low-polydispersity PA sphere systems with two different hard-core radii, R(0) = 542 and 1117 Å, are explored over a wide range of concentrations and salinities using static and dynamic light scattering (DLS), small angle x-ray scattering, and x-ray photon correlation spectroscopy (XPCS). The measured static and dynamic scattering functions are analyzed using state-of-the-art theoretical methods. For all samples, the measured static structure factor, S(Q), is in good agreement with results by an analytical integral equation method for particles interacting by a repulsive screened Coulomb plus hard-core pair potential. In our DLS and XPCS measurements, we have determined the short-time diffusion function D(Q) = D(0) H(Q)∕S(Q), comprising the free diffusion coefficient D(0) and the hydrodynamic function H(Q). The latter is calculated analytically using a self-part corrected version of the δγ-scheme by Beenakker and Mazur which accounts approximately for many-body hydrodynamic interactions (HIs). Except for low-salinity systems at the highest investigated volume fraction φ ≈ 0.32, the theoretical predictions for H(Q) are in excellent agreement with the experimental data. In particular, the increase in the collective diffusion coefficient D(c) = D(Q → 0), and the decrease of the self-diffusion coefficient, D(s) = D(Q → ∞), with increasing φ is well described. In accord with the theoretical prediction, the peak value, H(Q(m)), of H(Q) relates to the nearest neighbor cage size ∼2π∕Q(m), for which concentration scaling relations are discussed. The peak values H(Q(m)) are globally bound from below by the corresponding neutral hard-spheres peak values, and from above by the limiting peak values for low-salinity charge-stabilized systems. HIs usually slow short-time diffusion on colloidal length scales, except for the cage diffusion coefficient, D(cge) = D(Q(m)), in dilute low-salinity systems where a speed up of the system dynamics and corresponding peak values of H(Q(m)) > 1 are observed experimentally and theoretically.

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Section: B Wavenumber Dependent Diffusion and Scaling Relationscontrasting

confidence: 56%

Structure and short-time dynamics in concentrated suspensions of charged colloids

Westermeier

Fischer

Roseker

et al. 2012

The Journal of Chemical Physics

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“…The only input parameter required is the static structure factor S(q). The BM theory predictions were verified by XPCS in several different charge-stabilized suspensions with screened electrostatic interactions [15,17]. In the case of sterically-stabilized suspensions, interacting via a hard-sphere potential, the predictions of BM theory where verified by the two-color DLS experiments described in [5].…”

Section: Short-time Dynamics and Hydrodynamic Interactionsmentioning

confidence: 64%

“…Previous XPCS experiments on hydrodynamic effects in colloidal suspensions have focused on charge-stabilized particles [13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Dynamics in dense hard-sphere colloidal suspensions

et al. 2012

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The dynamic behavior of a hard-sphere colloidal suspension was studied by X-ray Photon Correlation Spectroscopy and Small Angle X-ray Scattering over a wide range of particle volume fractions. The short-time mobility of the particles was found to be smaller than that of free particles even at relatively low concentrations, showing the importance of indirect hydrodynamic interactions. Hydrodynamic functions were derived from the data and for moderate particle volume fractions (Φ ≤ 0.40) there is a good agreement with earlier many-body theory calculations by Beenakker and Mazur [C.W.J. Beenakker and P. Mazur, Physica A 120, 349 (1984)]. Important discrepancies appear at higher concentrations, above Φ ≈ 0.40, where the hydrodynamic effects are overestimated by the Beenakker-Mazur theory, but predicted accurately by an accelerated Stokesian dynamics algorithm developed by Banchio and Brady [A.J. Banchio and J. F. Brady, J. Chem. Phys. 118, 10323 (2003)]. For the relaxation rates, good agreement was also found between the experimental data and a scaling form predicted by Mode Coupling Theory. In the high concentration range, with the fluid suspensions approaching the glass transition, the long-time diffusion coefficient was compared with the short-time collective diffusion coefficient to verify a scaling relation previously proposed by Segrè and Pusey [P.N. Segrè and P.N. Pusey, Phys. Rev. Lett. 77, 771 (1996)]. We discuss our results in view of previous experimental attempts to validate this scaling law [L. Lurio et al., Phys. Rev. Lett. 84, 785 (2000)].

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“…3(a)] provides a tantalizing new way to measure hydrodynamics directly, with no additional data. For diffusing spheres, gðq; tÞ is an exponential at any for t less than the Brownian time B 4a 2 =D 0 [7]; g s ðq;tÞffiexp½Àt= s ðqÞ, where s ðqÞ¼ðD 0 q 2 Þ À1 SðqÞ=HðqÞ, and the hydrodynamic factor HðqÞ characterizes hydrodynamic interactions among particles [7,8]. We find that HðqÞ remains below 1 and decreases with increasing , expected for hard spheres [7] and consistent with previous x-ray photon correlation spectroscopy measurements [8], as shown with open symbols in Fig.…”

Section: (F)mentioning

confidence: 99%

Characterizing Concentrated, Multiply Scattering, and Actively Driven Fluorescent Systems with Confocal Differential Dynamic Microscopy

et al. 2012

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We introduce confocal differential dynamic microscopy (ConDDM), a new technique yielding information comparable to that given by light scattering but in dense, opaque, fluorescent samples of micron-sized objects that cannot be probed easily with other existing techniques. We measure the correct wave vector q-dependent structure and hydrodynamic factors of concentrated hard-sphere-like colloids. We characterize concentrated swimming bacteria, observing ballistic motion in the bulk and a new compressed-exponential scaling of dynamics, and determine the velocity distribution; by contrast, near the coverslip, dynamics scale differently, suggesting that bacterial motion near surfaces fundamentally differs from that of freely swimming organisms. DOI: 10.1103/PhysRevLett.108.218103 PACS numbers: 87.64.mk, 47.57.EÀ, 78.35.+c, 82.70.Dd Fluorescence imaging is an important and versatile form of optical microscopy. Fluorescent tags can selectively identify specific features within an image, thereby enhancing contrast; this is particularly powerful in biology and soft-matter physics. A major difficulty, however, is that all fluorescent objects within the illumination beam emit light, even if outside the microscope's focal plane, hindering collection of high-quality images. Using a confocal pinhole, which limits detected light to only that originating from the focal plane, confocal microscopy allows true 3D imaging. By its very nature, however, confocal microscopy is relatively slow; collecting a 3D stack of images usually requires several seconds, limiting the study of dynamics to relatively slow phenomena, characterized by time scales well in excess of a second [1,2].Even traditional bright field microscopy is limited in its ability to follow rapid dynamics; by contrast, another optical method, dynamic light scattering (DLS), is wellsuited to characterize dynamics at high speeds, specifically ensemble averages as a function of scattering wave vector q, albeit at the cost of losing real-space information [3]. One way to combine DLS with the advantages of real-space imaging in the wide field is differential dynamic microscopy (DDM), which extends to lower-q information analogous to that given by DLS [4-6]. However, DDM has thus far been restricted to wide field imaging; consequently, like DLS, DDM probes only dilute suspensions [4][5][6]. No equivalent method exists for fluorescence, particularly in high-concentration samples where imaging is obscured. This severely limits the use of fluorescence microscopy for studies of dynamics in dense samples.In this Letter, we introduce a new technique using confocal fluorescence microscopy that provides a powerful probe not only of rapid dynamics but also of the static structure of dense, fluorescent samples that multiply scatter light, precluding their study with other techniques. Motivated by DDM analysis, we examine the Fourier spectra of the differences between pairs of images within a sequence; the short-time differences confirm diffusive motion of hard-sphere-like colloidal ...

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Dynamics in dense suspensions of charge-stabilized colloidal particles

Cited by 20 publications

References 17 publications

Structure and short-time dynamics in concentrated suspensions of charged colloids

Structure and short-time dynamics in concentrated suspensions of charged colloids

Dynamics in dense hard-sphere colloidal suspensions

Characterizing Concentrated, Multiply Scattering, and Actively Driven Fluorescent Systems with Confocal Differential Dynamic Microscopy

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