Static properties of confined colloidal suspensions

Carbajal-Tinoco, Mauricio D.; Castro-Román, F.; Arauz‐Lara, José Luis

doi:10.1103/physreve.53.3745

Cited by 160 publications

(131 citation statements)

References 14 publications

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“…For example, all previous observations of confinement-induced attractions [2,4,8,9] were performed on polystyrene (PS) microspheres with highly acidic surface groups [10]. The only related study on confined silica spheres found no deviations from mean-field theory's predictions [10].…”

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confidence: 99%

“…Anomalous interactions therefore might be peculiar to highly charged spheres in general, or to PS in particular, in which case the effect would be far less generally important than originally supposed. Concern also has been raised that hydrodynamic coupling [11,12] or other experimental artifacts [10] might explain the observed attractions, particularly because error estimates were not available for some of the measurements [2,8].This Letter describes digital video microscopy measurements of the equilibrium pair potentials for charged colloidal spheres under varying degrees of confinement. These measurements reveal strong and long-ranged likecharge colloidal attractions not only between PS spheres confined to the midplane between parallel glass walls, but also between more weakly charged silica colloid sedimented into a monolayer above a glass wall.…”

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confidence: 99%

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Confinement-Induced Colloidal Attractions in Equilibrium

2003

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The Poisson-Boltzmann theory for colloidal electrostatic interactions predicts that charged colloidal spheres dispersed in water should repel each other, even when confined by charged surfaces. Direct measurements on highly charged polystyrene spheres, however, reveal strong, long-ranged confinementinduced attractions that have yet to be explained. We demonstrate that anomalous attractions also characterize the equilibrium pair potential for more weakly charged colloidal silica spheres sedimented into a monolayer above a glass surface. This observation substantially expands the range of conditions for which mean-field theory incorrectly predicts the sign of macroions' interactions, and provides new insights into how confinement induces long-ranged like-charge attractions. This problem's intractability reflects the complexity of the macroionic environment. Under equilibrium conditions, charge-stabilized colloidal particles' long-range interactions result from a combination of direct Coulomb repulsions and indirect interactions mediated by microscopic ions in solution. The spheres' effective pair potential, u r , is an average over the simple ions' degrees of freedom. The Poisson-Boltzmann formalism performs this average in the mean-field approximation and so cannot account for fluctuations or correlations in the simple ions' distributions. Thermodynamically selfconsistent liquid structure calculations demonstrate that particle-ion and ion-ion correlations indeed can mediate long-ranged attractions [6] consistent with metastable phase separation in bulk suspensions [7]. This mechanism's relevance to pairs of spheres confined by charged walls remains to be determined, however.The apparent subtlety of confinement-induced likecharge colloidal attractions has inspired a critical reassessment of the experimental evidence. For example, all previous observations of confinement-induced attractions [2,4,8,9] were performed on polystyrene (PS) microspheres with highly acidic surface groups [10]. The only related study on confined silica spheres found no deviations from mean-field theory's predictions [10]. Anomalous interactions therefore might be peculiar to highly charged spheres in general, or to PS in particular, in which case the effect would be far less generally important than originally supposed. Concern also has been raised that hydrodynamic coupling [11,12] or other experimental artifacts [10] might explain the observed attractions, particularly because error estimates were not available for some of the measurements [2,8].This Letter describes digital video microscopy measurements of the equilibrium pair potentials for charged colloidal spheres under varying degrees of confinement. These measurements reveal strong and long-ranged likecharge colloidal attractions not only between PS spheres confined to the midplane between parallel glass walls, but also between more weakly charged silica colloid sedimented into a monolayer above a glass wall. Even though the sedimented spheres' dynamics should be influenced princip...

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confidence: 99%

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Confinement-Induced Colloidal Attractions in Equilibrium

2003

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“…The Derjaguin-Landau-Verwey-Overbeek theory predicts that an isolated pair of highly charged macroparticles will experience a purely repulsive screened Coulomb interaction. This reasonable prediction was contradicted by the experimental observation [1,2].…”

Section: Introductionmentioning

confidence: 82%

The Anisotropic Cell Model in the Colloidal Plasmas

Ye¹,

Lu²

2010

PIER

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Abstract-The anisotropic spherical Wigner-Seitz (WS) cell model -introduced to describe colloidal plasmas -is investigated using the linearized Poisson-Boltzmann (PB) equation. As an approximation, the surface potential of the spherical macroparicle expanded in terms of the monopole (q) and the dipole (p) is considered as an anisotropic boundary condition of the linear PB equation. Here, the "apparent" moments q and p are the moments 'seen' in the microion cloud, respectively. Based on a new physical concept, the momentneutrality, the potential around the macroparticle can be solvable analytically if the relationship between the actual moment and the "apparent" moment can be obtained according to the momentneutrality condition in addition to the usual electroneutrality. The calculated results of the potential show that there is an attractive region in the vicinity of macroparticle when the corresponding dipole part of the potential dominates over the monopole part, and there is an attractive region and a repulsive region at the same time, i.e., a potential well, when the corresponding dipole part of the potential just comes into play. It provides the possibility and the conditions of the appearance of periodic structure of the colloidal plasmas, although it is a result of a simple theoretical model.

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“…[1,2,3,4,5,6] as well as by other groups [7,8], which show unexplained attraction between colloidal particles in suspension. As most other polymer aggregates do, the particles used in the experiments dissociate in the solvent with charges of one sign remaining on the surface of the particles and charges of the other sign going to the solvent.…”

Section: Introductionmentioning

confidence: 93%

Effects of Flow on Measurements of Interactions in Colloidal Suspensions

Popov

2002

Journal of Colloid and Interface Science

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A hydrodynamic mechanism of interactions of colloidal particles is considered. The mechanism is based on the assumption of tiny background flows in the experimental cells during measurements by Grier at al. [1,2,3,4,5,6]. Both trivial (shear flow) and non-trivial (force propagation through viscous fluid) effects are taken into account for two colloidal particles near a wall bounding the solvent. Expressions for the radial (attractive or repulsive) forces and the polar torques are obtained. Quantitative estimates of the flow needed to produce the observed strength of attractive force are given, other necessary conditions are also considered. The conclusion is made: the mechanism suggested most likely is not responsible for the attractive interactions observed in the experiments of Grier at al.; however, it may be applicable in other experimental realizations and should be kept in mind while conducting colloidal measurements of high sensitivity. Several distinctive features of the interactions due to this mechanism are identified.

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Static properties of confined colloidal suspensions

Cited by 160 publications

References 14 publications

Confinement-Induced Colloidal Attractions in Equilibrium

Confinement-Induced Colloidal Attractions in Equilibrium

The Anisotropic Cell Model in the Colloidal Plasmas

Effects of Flow on Measurements of Interactions in Colloidal Suspensions

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