17 research outputs found
Observation of liquid glass in suspensions of ellipsoidal colloids
Despite the omnipresence of colloidal suspensions, little is known about the
influence of shape on phase transformations, especially in nonequilibrium. To
date, real-space imaging results are limited to systems composed of spherical
colloids. In most natural and technical systems, however, particles are
non-spherical and their structural dynamics are determined by translational and
rotational degrees of freedom. Using confocal microscopy, we reveal that
suspensions of ellipsoidal colloids form an unexpected state of matter, a
liquid glass in which rotations are frozen while translations remain fluid.
Image analysis unveils hitherto unknown nematic precursors as characteristic
structural elements of this state. The mutual obstruction of these ramified
clusters prevents liquid crystalline order. Our results give unique insight
into the interplay between local structures and phase transformations. This
helps to guide applications such as self-assembly of colloidal superstructures
and also gives first evidence of the importance of shape on the glass
transition in general.Comment: 19 pages, 6 figures; additional SI; submitte
Shape and scale dependent diffusivity of colloidal nanoclusters and aggregates
© 2016, EDP Sciences and Springer.The diffusion of colloidal nanoparticles and nanomolecular aggregates, which plays an important role in various biophysical and physicochemical phenomena, is currently under intense study. Here, we examine the shape and size dependent diffusion of colloidal nano- particles, fused nanoclusters and nanoaggregates using a hybrid fluctuating lattice Boltzmann-Molecular Dynamics method. We use physically realistic parameters characteristic of an aqueous solution, with explicitly implemented microscopic no-slip and full-slip boundary conditions. Results from nanocolloids below 10 nm in radii demonstrate how the volume fraction of the hydrodynamic boundary layer influences diffusivities. Full-slip colloids are found to diffuse faster than no-slip particles. We also characterize the shape dependent anisotropy of the diffusion coefficients of nanoclusters through the Green-Kubo relation. Finally, we study the size dependence of the diffusion of nanoaggregates comprising Nââ€â108 monomers and demonstrate that the diffusion coefficient approaches the continuum scaling limit of Nâ1/3
Rhéologie et structuration des suspensions céramiques sous contraintes : une étude numérique
The main objective of this thesis is to predict and understand the structural and rheological properties of colloidal suspensions when (1) hydrodynamic interactions (HIs) and/or (2) external forces are present. We employ two of the fastest techniques in literature: Brownian dynamics (BD), for systems without HIs; and the hybrid "stochastic rotation dynamics - molecular dynamics" (SRD-MD) for systems with HIs. Three different systems were studied. The first is a system of hard spheres subjected to shear, where the goal was to ensure that SRD-MD can correctly reproduce the viscosity vs. volume fraction relationship. The results are consistent with known analytical, numerical and experimental data. The second system is an alumina suspension described by the DLVO theory (Derjaguin-Landau-Verwey-Overbeek). The simulations show that the percolation threshold (phi_c) decreases as the depth of the potential well increases. Moreover, we note that HIs tend to form more elongated structures compared to the systems without HIs. The phi_c values ââobtained are in good agreement with those estimated by Flatt and Bowen's yield stress model (YODEL). The third system consists of binary colloids that interact by Yukawa potential and subjected to the influence of an attractive wall. We show that the presence of an attractive wall may alter the crystalline structures such that CsCl crystals are formed instead of the metastable NaCl crystals. Finally, we conducted a preliminary study of suspensions under an oscillating shear. We show that when the aggregation process suspension coincides with the oscillatory motion, more compact structures are formed.L'enjeu principal de cette thĂšse est de comprendre et prĂ©dire les propriĂ©tĂ©s structurales et rhĂ©ologiques de suspensions colloĂŻdales en tenant compte d'Ă©lĂ©ments complexes tels que (1) les interactions hydrodynamiques (IHs) et/ou (2) des forces extĂ©rieures. Nous employons dans cette thĂšse deux des techniques numĂ©riques les plus rapides de la littĂ©rature: la dynamique brownienne standard (BD), pour les systĂšmes oĂč les IHs peuvent ĂȘtre ignorĂ©es; et la technique hybride "stochastic rotation dynamics - molecular dynamics" (SRD-MD), pour les systĂšmes oĂč les IHs doivent ĂȘtre incorporĂ©es.Trois systĂšmes colloĂŻdaux diffĂ©rents ont Ă©tĂ© Ă©tudiĂ©s. Le premier est un systĂšme de sphĂšres dures soumis Ă un cisaillement, oĂč le but a Ă©tĂ© de vĂ©rifier que l'introduction des IHs dans la SRD-MD peut correctement reproduire la relation entre la viscositĂ© et la fraction volumique. Les rĂ©sultats de viscositĂ© sont en accord avec les rĂ©sultats connus, qu'ils soient analytiques, numĂ©riques et expĂ©rimentaux. Le second systĂšme consiste en une suspension d'alumine, pour laquelle les interactions sont dĂ©crites par la thĂ©orie DLVO (Derjaguin-Landau-Verwey-Overbeek). Les simulations montrent que le seuil de percolation (phi_c) diminue lorsque la profondeur du puits de potentiel augmente. De plus, nous observons que la prise en compte des IHs tend Ă former des structures plus allongĂ©es Ă©galement, par rapport aux structures obtenues sans les IHs. Les valeurs de phi_c obtenues dans les simulations sont en bon accord avec celles estimĂ©es par le modĂšle de la contrainte seuil (YODEL) Ă©tabli par Flatt et Bowen. Le troisiĂšme systĂšme comporte deux types de colloĂŻdes qui interagissent par un potentiel de Yukawa. Ce systĂšme binaire est soumis Ă l'influence d'un mur attractif. Nous montrons que la prĂ©sence d'un mur attractif peut altĂ©rer la structure cristalline des agrĂ©gats Ă la surface telle qu'une structure de type CsCl qui se forme au lieu de la structure mĂ©tastable de type NaCl. Finalement, nous avons rĂ©alisĂ© une Ă©tude prĂ©liminaire par SRD-MD de suspensions soumises Ă un cisaillement oscillant. Nous montrons que lorsque la suspension est soumise au cisaillement oscillant en mĂȘme temps que l'agrĂ©gation se produit, des structures plus compactes se forment
Aggregation of binary colloidal suspensions on attractive walls
reserved5siThe adsorption of colloidal particles from a suspension on a solid surface is of fundamental importance to many physical and biological systems. In this work, Brownian Dynamics simulations are performed to study the aggregation in a suspension of oppositely charged colloidal particles in the presence of an attractive wall. For sufficiently strong attractions, the wall alters the microstructure of the aggregates so that B2 (CsCl-type) structures are more likely obtained instead of B1 (NaCl-type) structures. The probability of forming either B1 or B2 crystallites depends also on the inverse interaction range Îșa. Suspensions with small Îșa are more likely to form B2 crystals than suspensions with larger Îșa, even if the energetic stability of the B2 phase decreases with decreasing Îșa. The mechanisms underlying this aggregation and crystallization behaviour are analyzed in detail.mixedLaganapan, Aleena; Bochicchio, Davide; Bienia, Marguerite; Videcoq, Arnaud; Ferrando, RiccardoLaganapan, Aleena; Bochicchio, Davide; Bienia, Marguerite; Videcoq, ARNAUD JEAN PIERRE; Ferrando, Riccard
Determination of the shear viscosity in mesoscopic simulations of ceramic colloidal suspensions
International audienc
Importance des interactions hydrodynamiques dans les simulations mésoscopiques pour prédire le comportement rhéologique des suspensions céramiques
National audienc
SRD-MD Modelling of hydrodynamic interactions in colloidal systems: playing between computational cost and resolution
International audienc
Mesoscopic modelling of hydrodynamic interactions in colloidal suspensions
International audienc
Shear viscosity in hard-sphere and adhesive colloidal suspensions with reverse non-equilibrium molecular dynamics
International audienc