How Insulating Particles Increase the Conductivity of a Suspension

Pannacci, Nicolas; Lobry, Laurent; Lemaire, Élisabeth

doi:10.1103/physrevlett.99.094503

Cited by 35 publications

(51 citation statements)

References 12 publications

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“…From the steady solution of the Quincke rotation in an infinite fluid, we can calculate the unperturbed dipole P in the absence of the surface, and then evaluate the disturbance field due to the surface. Whithin our experimental conditions, E 0 < 3E Q and χ ∞ 1 2 [28]. Therefore, the correction δE is much smaller that the magnitude of the unperturbed field: |δE |/E 0 ∼ 0.01.…”

Section: B Self-propulsion Of a Quincke Rollermentioning

confidence: 77%

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Emergence of macroscopic directed motion in populations of motile colloids

Bricard¹,

Caussin²,

Desreumaux³

et al. 2013

Nature

895

1,029

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From the formation of animal flocks to the emergence of coordinate motion in bacterial swarms, at all scales, populations of motile organisms display coherent collective motion.This consistent behavior strongly contrasts with the difference in communication abilities between the individuals. Guided by this universal feature, physicists have proposed that solely alignment rules at the individual level could account for the emergence of unidirectional motion at the group level [1][2][3][4] . This hypothesis has been supported by agent-based simulations 1,5,6 . However, more complex collective behaviors have been systematically found in experiments including the formation of vortices 7-9 , fluctuating swarms 7, 10 , clustering 11,12 , and swirling [13][14][15][16] . All these (living and man-made) model systems (bacteria 9,10, 16 , biofilaments and molecular motors 7,8,13 , shaken grains 14, 15 and reactive colloids 11,12 ) predominantly rely on actual collisions to display collective motion. As a result, the potential local alignment rules are entangled with more complex, and often unknown, interactions. The large-scale behaviour of the populations therefore strongly depends on these uncontrolled microscopic couplings that are extremely challenging to measure and describe theoretically.Here, we demonstrate a new phase of active matter. We reveal that dilute populations of millions of colloidal rollers self-organize to achieve coherent motion along a unique direction, with very few density and velocity fluctuations. Identifying, quantitatively, the microscopic interactions between the rollers allows a theoretical description of this polar-liquid state. Comparison of the theory with experiment suggests that hydrodynamic interactions promote the emergence of collective motion either in the form of a single macroscopic flock at low densities, or in that of a homogenous polar phase at higher densities. Furthermore, hydrodynamics protects the polar-liquid state from the giant density fluctuations, which were hitherto considered as the hallmark of populations of self-propelled particles 2, 3, 17 . Our experiments demonstrate that genuine physical interactions at the individual level are sufficient to set homogeneous active populations into stable directed motion.Our system consists of large populations of colloids capable of self-propulsion and of sensing the orientation of their neighbors solely by means of physical mechanisms. We take advantage of an overlooked electrohydrodynamic phenomenon referred to as the Quincke rotation 18,19 (Fig. 1a).When an electric field E 0 is applied to an insulating sphere immersed in a conducting fluid, above a critical field amplitude E Q , the charge distribution at the sphere's surface is unstable to infinitesimal fluctuations. This spontaneous symmetry breaking results in a net electrostatic torque, which causes the sphere to rotate at a constant speed around a random direction transverse to E 0 18 . We 2 exploit this instability to engineer self-propelled colloidal rollers. We use ...

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Section: B Self-propulsion Of a Quincke Rollermentioning

confidence: 77%

“…As our theory does not involve any phenomenological parameter, we can provide an estimate of both the Quincke threshold and the intrinsic velocity scale of the rollers. We have a = 2.4 µm, η ∼ 2 mPa · s −1 , l ∼ 2 0 and τ ∼ 1 ms [28]. So using the expressions below Eq.…”

Section: B Self-propulsion Of a Quincke Rollermentioning

confidence: 99%

Emergence of macroscopic directed motion in populations of motile colloids

Bricard¹,

Caussin²,

Desreumaux³

et al. 2013

Nature

895

1,029

View full text Add to dashboard Cite

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“…The Quincke rotation instability has these characteristics: The rotation axis is always normal to the applied electric field, the frequency of rotation and the critical electric field is independent of the size of the bead, and the rotation frequency increases with the applied electric field [3,4]. The onset of Quincke rotation in suspensions can lead to several remarkable effects such as effective viscosity reduction [5,6] and increased effective electric conductivity of suspensions [7]. Quincke rotating colloidal particles have been observed to "roll" with a constant velocity on surfaces in liquid crystals and on bubbles [8].…”

Section: Introductionmentioning

confidence: 99%

Electro-hydrodynamic propulsion of counter-rotating Pickering drops

Dommersnes

Mikkelsen

Fossum

2016

Eur. Phys. J. Spec. Top.

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Insulating particles or drops suspended in carrier liquids may start to rotate with a constant frequency when subjected to a uniform DC electric field. This is known as the Quincke rotation electro-hydrodynamic instability. A single isolated rotating particle exhibit no translational motion at low Reynolds number, however interacting rotating particles may move relative to one another. Here we present a simple system consisting of two interacting and deformable Quincke rotating particle covered drops, i.e. deformable Pickering drops. The drops attract one another and spontaneously form a counter-rotating pair that exhibits electro-hydrodynamic driven propulsion at low Reynolds number flow.

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“…The dipole moment P is named "retarded dipole moment" and is given by a relaxation equation [Pannacci (2007a)]:…”

Section: A Mechanism Of Quincke Rotationmentioning

confidence: 99%

Viscosity of an electro-rheological suspension with internal rotations

Lemaire¹,

Lobry²,

Pannacci³

et al. 2008

Journal of Rheology

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SynopsisThe rheological behaviour of a suspension of insulating particles dispersed in a slightly conducting liquid under the action of a DC electric field is studied. The polarisation of the particles induced by the field is shown to be responsible for a rotation of the particles (Quincke rotation) which, in turn, leads to a drastic decrease of the apparent viscosity of the suspension. The purpose of the paper is to provide a relation between the apparent viscosity of the suspension and the E field intensity. First, the steady state solutions are searched for the angular velocity of a particle subjected to both DC E field and simple shear flow. Since the solutions are multivalued, their stability is studied using a linear stability analysis. Then, the stable solution for the particle angular velocity is used to deduce the value of the apparent viscosity of the suspension. The predictions of the model are compared to experimental data which have been obtained on a suspension of PMMA particles dispersed in a low polar dielectric liquid. The agreement between experiments and theory is rather good even if the model overestimates the viscosity decrease induced by the field.2

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How Insulating Particles Increase the Conductivity of a Suspension

Cited by 35 publications

References 12 publications

Emergence of macroscopic directed motion in populations of motile colloids

Emergence of macroscopic directed motion in populations of motile colloids

Electro-hydrodynamic propulsion of counter-rotating Pickering drops

Viscosity of an electro-rheological suspension with internal rotations

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