Heteroaggregation, repeptization and stability in mixtures of oppositely charged colloids

Raşa, M.; Philipse, Albert P.; Meeldijk, Johannes D.

doi:10.1016/j.jcis.2004.05.020

Cited by 46 publications

(28 citation statements)

References 15 publications

(25 reference statements)

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“…The behavior shown by the negative silica-positive magnetite mixtures, in our case the potentials are −20.4 mV for silica vs 32 mV for magnetite, can be explained in terms of charge inversion, using arguments similar to those proposed in [10]: since silica particles have a significant solubility, the dissolved silicate species may adsorb on a positively charged surface to reverse its charge sign.…”

Section: Discussionsupporting

confidence: 71%

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Stability of mixtures of charged silica, silica–alumina, and magnetite colloids

Viota

Raşa

Sacanna

et al. 2005

Journal of Colloid and Interface Science

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We report experiments on the stability of aqueous mixtures of charged colloidal magnetite and charged silica and silica covered with alumina particles of similar size. First, positively charged magnetite dispersions were mixed with negatively charged silica dispersions at pH 4, at different volume ratios and low colloid volume fractions, producing mixtures which were stable over a period of weeks despite the expected electrostatic attraction between the oppositely charged particles. When magnetite particles were mixed with positively charged silica covered with alumina at pH 4 under exactly the same conditions, some of the systems separated to form a magnetite sediment. When the volume fraction of the initial dispersions was increased, the behavior of the mixtures was the opposite: positive magnetite/negative silica mixtures were unstable at intermediate volume ratios. The unexpected behavior of the mixtures was investigated by means of electrophoretic mobility, initial susceptibility, and dynamic light scattering measurements as well as sedimentation experiments.  2005 Elsevier Inc. All rights reserved.

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Section: Discussionsupporting

confidence: 71%

“…In Ref. [10], Raşa et al studied heteroaggregation of oppositely charged silica particles of similar size and reported, among other things, repeptization of aggregates due to charge inversion of the negative silica particles.…”

Section: Introductionmentioning

confidence: 99%

Stability of mixtures of charged silica, silica–alumina, and magnetite colloids

Viota

Raşa

Sacanna

et al. 2005

Journal of Colloid and Interface Science

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“…There was increasing adsorption with increasing nanoparticle concentration as well. Looking at Figures 11,12,13,and 15, it is clear that the particles adsorbed in relatively large quantities, over 600 particles per μm 2 as the pH approached 2.0, or an approximate surface coverage of 24% (this is a rough estimate using the cross-sectional area of a 22 nm sphere as the area covered by a single particle; it should be noted that this estimation would not quite equal 100% coverage even with particles ideally packed on the surface as there would theoretically be gaps between the spherical particles).…”

Section: Discussionmentioning

confidence: 99%

“…The effects of additional material in a colloidal solution have been studied for decades, whether it is with the addition of polymer, polyelectrolyte, nanoparticles, or even microparticles [11][12][13][14][15]. One well documented effect of adding non-adsorbing nanoparticles or polyelectrolyte on colloidal stability is flocculation due to the "depletion" force, which has been observed and studied since the 1920s [12].…”

Section: Introductionmentioning

confidence: 99%

Stabilization of Weakly Charged Microparticles Using Highly Charged Nanoparticles

Herman

Walz

2013

Langmuir

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An experimental investigation was conducted to evaluate the possible use of highlycharged spherical nanoparticles to stabilize an aqueous dispersion of weakly-charged microspheres. At low pH values, the surface of silica is weakly charged, which leads to flocculation of colloidal suspensions of silica microspheres. Binary solutions of weakly charged silica microspheres and highly charged polystyrene latex nanoparticles result in adsorption of the nanoparticles onto the surface of the silica microspheres. This effectively "recharges" the silica spheres, with effective zeta potentials increased to the range that is unfavorable for flocculation of microspheres in a silica-only solution. However, this does not guarantee stability, and comparisons between positively charged amidine latex nanoparticles and negatively charged sulfate latex nanoparticles indicate that the degree of coverage plays an important role in the restabilization. The sulfate latex nanoparticles do not cover the surface sufficiently, and though they seemingly provide sufficient charge, the weakly charged patches of the exposed silica substrate can lead to flocculation. The amidine latex nanoparticles, on the other hand, cover the surface more completely, and effectively prevent flocculation of the silica microspheres. The mechanisms responsible for this different adsorption and stabilizing behavior are not entirely understood, as both the amidine and sulfate latex nanoparticles are of similar size and the magnitude of the zeta potentials of the different particle types are comparable.iii

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“…The electrostatic interaction between two large NPs can be approximated by a screened potential (29), in which the effective screening length decreases with increasing concentration of screening charge carriers (here, small NPs) and determines the stability of dispersed nanoparticles. When large NPs are surrounded by smaller, oppositely charged ones, the effective screening length is small, and the NPs interact weakly and do not aggregate (30,31). In contrast, when no small particles are present, the screening length is large, long-range attractive electrostatic forces are strong, and flocculation (32) ensues.…”

Section: Wwwsciencemagorg Science Vol 312 21 April 2006mentioning

confidence: 99%

Electrostatic Self-Assembly of Binary Nanoparticle Crystals with a Diamond-Like Lattice

Kalsin

Fiałkowski

Paszewski

et al. 2006

Science

877

881

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Self-assembly of charged, equally sized metal nanoparticles of two types (gold and silver) leads to the formation of large, sphalerite (diamond-like) crystals, in which each nanoparticle has four oppositely charged neighbors. Formation of these non-close-packed structures is a consequence of electrostatic effects specific to the nanoscale, where the thickness of the screening layer is commensurate with the dimensions of the assembling objects. Because of electrostatic stabilization of larger crystallizing particles by smaller ones, better-quality crystals can be obtained from more polydisperse nanoparticle solutions.C rystalline aggregates composed of one or more types of metallic and/or semiconductor nanoparticles (NPs) are of great interest for the development of new materials with potential applications in areas such as optoelectronics (1), high-density data storage (2), catalysis (3), and biological sensing (4). To date, methods for the crystallization of two-dimensional (2D) and 3D NP superlattices have relied on the differences in the sizes of component particles and on attractive van der Waals or hard-sphere interactions between them. This strategy has been successful in preparing several types of lattices Esuch as AB (5), AB 2 (6), AB 5 (7), and AB 13 (6)^, but the all-attractive nature of the interparticle potentials limits its applicability to relatively few and usually (8) close-packed structures.To overcome this limitation, we and others (8, 9) have focused on systems of NPs interacting via electrostatic forces; such forces provide a basis for ionic, colloidal (9), or even macroscopic (10) crystals, but, despite promising attempts (8, 11), have not been successfully exploited for controllable or predictable long-range organization of matter at the nanoscale. Here, we report electrostatic self-assembly (10) (ESA) of oppositely charged, nearly equally sized metallic NPs of different types into large 3D crystals characterized by sphalerite (diamond-like) (12) internal packing, and of overall morphologies identical to those of macroscopic diamond or sphalerite crystals (Figs. 1 to 4). Formation of these nonclose-packed structures results from the change in electrostatic interactions in the nanoscopic regime, where the thickness of the screening layer becomes commensurate with the dimensions of the assembling particles, and is facilitated by the presence of smaller, charged NPs in the crystallizing solutions that stabilize larger NPs by what can be termed a nanoscopic counterpart of Debye screening.We used Ag and Au NPs coated with w-functionalized alkane thiols (13): HS(CH 2 ) 10 COOH (MUA) and HS(CH 2 ) 11 NMe 3 þ Cl j (TMA) (Fig. 1A). These NPs were prepared according to a modified procedure (14) Esee Supporting Online Material (15)^and had average diameters of 5.1 nm (with dispersity s 0 20%) for Au and 4.8 nm (s 0 30%) for Ag (Fig. 1B). We chose this pair as a model system, because the average sizes of Au NPs passivated with MUA Eself-assembled monolayer (SAM) thickness 0 1.63 nm (16)^and Ag NPs cov...

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Heteroaggregation, repeptization and stability in mixtures of oppositely charged colloids

Cited by 46 publications

References 15 publications

Stability of mixtures of charged silica, silica–alumina, and magnetite colloids

Stability of mixtures of charged silica, silica–alumina, and magnetite colloids

Stabilization of Weakly Charged Microparticles Using Highly Charged Nanoparticles

Electrostatic Self-Assembly of Binary Nanoparticle Crystals with a Diamond-Like Lattice

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