Electric-field-induced pattern formation in colloidal dispersions

Trau, Matt; Sankaran, Subramanian; Saville, D. A.; Aksay, İlhan A.

doi:10.1038/374437a0

Cited by 96 publications

(70 citation statements)

References 12 publications

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“…The electrokinetic mechanisms responsible for particle concentration are AC frequency dependent. Low-frequency planar colloidal aggregate formation and patterning was demonstrated originally by Trau et al 15 and since has been extensively investigated. [16][17][18] Their formation was attributed to induced electrohydrodynamic flows on the surface of the electrode that carry particles towards each other.…”

Section: Experiments and Methodsmentioning

confidence: 99%

A simple, optically induced electrokinetic method to concentrate and pattern nanoparticles

et al. 2009

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We demonstrate an optically induced electrokinetic technique that continuously concentrates nanoparticles on the surface of a parallel plate electrode that is biased with an AC signal. A highly focused beam of near-infrared light (1064 nm) was applied, inducing an electrothermal microfluidic vortex that carried nanoparticles to its center where they were accumulated. This technique was demonstrated with 49 nm and 100 nm fluorescent polystyrene particles and characterized as a function of applied AC frequency and voltage. With this technique the location and shape of colloidal concentration was reconfigured by controlling the optical landscape, yielding dynamic control of the aggregation. Colloidal concentration was demonstrated with a plain parallel plate electrode configuration without the need of photoconductive materials or complex microfabrication procedures.

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Section: Experiments and Methodsmentioning

confidence: 99%

A simple, optically induced electrokinetic method to concentrate and pattern nanoparticles

et al. 2009

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“…The spheres do not engage in electrochemical reactions, and their fixed charges favor a departure from local electroneutrality in the surrounding electrolyte. 1 Once the ionic fluxes are spatially separated, they entrain counterpropagating flows of water around the spheres. [1][2][3] These flows exert hydrodynamic forces on the spheres, and their motions, in turn, redirect the flows.…”

Section: Introductionmentioning

confidence: 99%

“…1 Once the ionic fluxes are spatially separated, they entrain counterpropagating flows of water around the spheres. [1][2][3] These flows exert hydrodynamic forces on the spheres, and their motions, in turn, redirect the flows. [2][3][4][5] We previously reported 6,7 that the interplay of microscopic electrohydrodynamic flows around individual spheres can give rise to large-scale convective instabilities characterized by highly organized flow patterns involving thousands of spheres.…”

Section: Introductionmentioning

confidence: 99%

Colloidal electroconvection in a thin horizontal cell. II. Bulk electroconvection of water during parallel-plate electrolysis

Han

Grier

2006

The Journal of Chemical Physics

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We recently have reported [ J. Chem. Phys. 122, 164701 (2005)] a family of electroconvective patterns that arise when charge-stabilized colloidal dispersions are driven by constant (dc) vertical electric fields. Competition between gravity and electrokinetic forces acting on the individual spheres in this system leads to the formation of highly organized convective instabilities involving hundreds of spheres. Here, we report a distinct class of electroconvective patterns that emerge in confined aqueous dispersions at higher biases. These qualitatively resemble the honeycomb and labyrinthine patterns formed during thermally driven RayleighBénard convection, but arise from a distinct mechanism. Unlike the localized colloidal electroconvective patterns observed at lower biases, moreover, these system-spanning patterns form even without dispersed colloidal particles. Rather, they appear to result from an underlying electroconvective instability during electrolysis in the parallel plate geometry. This contrasts with recent theoretical results suggesting that simple electrolytes are linearly stable against electroconvection. We recently have reported ͓J. Chem. Phys. 122, 164701 ͑2005͔͒ a family of electroconvective patterns that arise when charge-stabilized colloidal dispersions are driven by constant ͑dc͒ vertical electric fields. Competition between gravity and electrokinetic forces acting on the individual spheres in this system leads to the formation of highly organized convective instabilities involving hundreds of spheres. Here, we report a distinct class of electroconvective patterns that emerge in confined aqueous dispersions at higher biases. These qualitatively resemble the honeycomb and labyrinthine patterns formed during thermally driven Rayleigh-Bénard convection, but arise from a distinct mechanism. Unlike the localized colloidal electroconvective patterns observed at lower biases, moreover, these system-spanning patterns form even without dispersed colloidal particles. Rather, they appear to result from an underlying electroconvective instability during electrolysis in the parallel plate geometry. This contrasts with recent theoretical results suggesting that simple electrolytes are linearly stable against electroconvection. Disciplines Physical Sciences and Mathematics | Physics

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“…Phase transitions and clustering instability of the electrostatically driven granular gas were found. The studies of self-assembly of colloidal particles in aqueous solutions revealed the importance of self-induced electrohydrodynamic (EHD) convective flows on the formation of various precipitate states [4,7,8,9,10]. Ordered clusters of particles vibrated in liquid were studied in Ref.…”

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confidence: 99%

Dynamic Self-Assembly and Patterns in Electrostatically Driven Granular Media

et al. 2003

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We show that granular media consisting of metallic microparticles immersed in a poorly conducting liquid in strong DC electric field self-assemble a rich variety of novel phases. These phases include static precipitate: honeycombs and Wigner crystals; and novel dynamic condensate: toroidal vortices and pulsating rings. The observed structures are explained by the interplay between charged granular gas and electrohydrodynamic convective flows in the liquid.PACS numbers: 45.70.Qj,05.65.+b,47.15.Cb,47.55.Kf Understanding the unifying principles of self-assembly of complex systems such as macro-molecules [1], diblock copolymers [2], micro-magnetic systems [3], ensembles of charged particles [4] is the key to future advances in nanoscience. Large ensembles of small particles display fascinating collective behavior when they acquire an electric charge and respond to competing long-range electromagnetic and short-range contact forces. Many industrial technologies face the challenge of assembling and separating such single-or multi-component micro and nano-size ensembles. The dynamics of conducting microparticles in electric field in the air was studied in [5,6]. Phase transitions and clustering instability of the electrostatically driven granular gas were found. The studies of self-assembly of colloidal particles in aqueous solutions revealed the importance of self-induced electrohydrodynamic (EHD) convective flows on the formation of various precipitate states [4,7,8,9,10]. Ordered clusters of particles vibrated in liquid were studied in Ref. [11].In this Letter we report new dynamic phenomena occurring in granular gas in poorly conducting liquid subject to strong electric field (up to 20 kV/cm). We show that metallic particles (120 µm diameter Bronze spheres) immersed in a toluene-ethanol mixture in DC electric field self-assemble into a rich variety of novel phases. These phases include static precipitates: honeycombs and Wigner crystals; and novel dynamic condensates: toroidal vortices and pulsating rings (Figs. 1 and 2). The observed phenomena are attributed to interaction between particles and EHD flows produced by the action of the electric field on ionic charges in the bulk of liquid. This provides a new mechanism for self-assembly of microparticles in non-aqueous solutions.To form the electro-cell, granular media consisting of 3 g (about 0.5 × 10 6 ) mono-dispersed 120 µm bronze spheres was placed into a 1.5 mm gap between two horizontal 12.5×12.5 cm glass plates covered by a transparent conducting layer of indium tin-dioxide (the particles constitute less than a monolayer coverage on the bottom plate). An electric field perpendicular to the plates was created by a DC high voltage source (0-3 kV) connected to the inner surface of each plate [5,6]. The liquid was introduced into the cell through two teflon microcapillaries connected to opposing side walls of the cell. Real time images were acquired using a high speed, up to 1000 frames per second, digital camera suspended over the transparent glass plates of...

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Electric-field-induced pattern formation in colloidal dispersions

Cited by 96 publications

References 12 publications

A simple, optically induced electrokinetic method to concentrate and pattern nanoparticles

A simple, optically induced electrokinetic method to concentrate and pattern nanoparticles

Colloidal electroconvection in a thin horizontal cell. II. Bulk electroconvection of water during parallel-plate electrolysis

Dynamic Self-Assembly and Patterns in Electrostatically Driven Granular Media

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