Negative mobility and sorting of colloidal particles

Eichhorn, Ralf; Regtmeier, Jan; Anselmetti, Dario; Reimann, Peter

doi:10.1039/b918716m

Cited by 58 publications

(47 citation statements)

References 66 publications

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“…1(a), both elements of the friction matrix decrease upon approaching walls, whereas near the center of the slit, they both approach their bulk isotropic value given by Eq. (10). By inverting the friction matrix, via Eq.…”

Section: Resultsmentioning

confidence: 99%

“…Recent studies have shown that the coupling between the system and the geometrical constraints overimposed by the environment can be relevant in situations such as molecular transport in zeolites, 3 ionic channels, 4 or in microfluidic devices. 5,6 Moreover, geometrical constraints can induce novel dynamical scenarios, such as particle separation, 7 cooperative rectification, 8,9 and negative mobility 10,11 that are absent in the behavior of the corresponding systems in bulk.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Tracer diffusion of hard-sphere binary mixtures under nano-confinement

Marconi

Malgaretti

Pagonabarraga

2015

The Journal of Chemical Physics

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Articles you may be interested inThe isotropic-nematic and nematic-nematic phase transition of binary mixtures of tangent hard-sphere chain fluids: An analytical equation of state J. Chem. Phys. 140, 034504 (2014) The physics of diffusion phenomena in nano-and microchannels has attracted a lot of attention in recent years, due to its close connection with many technological, medical, and industrial applications. In the present paper, we employ a kinetic approach to investigate how the confinement in nanostructured geometries affects the diffusive properties of fluid mixtures and leads to the appearance of properties different from those of bulk systems. In particular, we derive an expression for the friction tensor in the case of a bulk fluid mixture confined to a narrow slit having undulated walls. The boundary roughness leads to a new mechanism for transverse diffusion and can even lead to an effective diffusion along the channel larger than the one corresponding to a planar channel of equivalent section. Finally, we discuss a reduction of the previous equation to a one dimensional effective diffusion equation in which an entropic term encapsulates the geometrical information on the channel shape. C 2015 AIP Publishing LLC.[http://dx

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tracer diffusion of hard-sphere binary mixtures under nano-confinement

Marconi

Malgaretti

Pagonabarraga

2015

The Journal of Chemical Physics

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“…Local velocity inversion allows for negative mobility, where tracers displace on average against the net driving force [26,27]. This phenomenon is more clearly appreciated for neutral tracers, for which we can gain more insight because local electric forces do not compete with flow-induced drag.…”

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confidence: 94%

Entropic Electrokinetics: Recirculation, Particle Separation, and Negative Mobility

2014

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We show that when particles are suspended in an electrolyte confined between corrugated charged surfaces, electrokinetic flows lead to a new set of phenomena such as particle separation, mixing for low-Reynolds micro-and nano-metric devices and negative mobility. Our analysis shows that such phenomena arise, for incompressible fluids, due to the interplay between the electrostatic double layer and the corrugated geometrical confinement and that they are magnified when the width of the channel is comparable to the Debye length. Our characterization allows us to understand the physical origin of such phenomena therefore shading light on their possible relevance in a wide variety of situations, ranging from nano-and micro-fluidic devices to biological systems.PACS numbers: 82.39. Wj,47.56.+r,47.61.Fg The recent development of nano-and micro-fluidic devices [1] as well as cellular regulation mechanisms and cellular signaling [2] rely on the transport of ions across channels or pores whose sections range from the nanometric to the micrometric scale [3][4][5]. The transport across such conduits has been characterized, even for varying-section channels [6][7][8][9][10][11], assuming that the channel width, h(x), is large compared to the Debye length, κ −1 , over which the electrolyte charge distributes in the neighborhood of the charged channel wall (κh(x) ≫ 1), or in the absence of electrolytes [12]. Nowadays, the continuous process of device miniaturization and the widening of the range of achievable salt concentrations require an understanding of the behavior of such systems when the relevant length scales compete with each other [13]. Such regimes are already exploitable in different microand nano-fluidic experiments [3,4] and can be relevant in a variety of biological systems [14,15].In this Letter we will show that, precisely in this regime, i.e. when the Debye length and the channel aperture are comparable in size, κh(x) ∼ 1, an electrolyte embedded in a corrugated channel develops new transport regimes that can be exploited to separate suspended particles, control electric and mass currents and eventually induce negative mobility. When κh(x) ∼ 1, the electrolyte response to external forcing, such as electrostatic fields, is very sensitive to the channel shape and it develops a recirculating region in which the electrolyte flows on the opposite direction as compared to the average volume flow, as shown in Fig. 1.A. Such a phenomenon, typical for incompressible fluids, is due to the interplay between the electrostatic double layer and the varying geometrical confinement and its magnitude is significantly amplified when κh(x) ∼ 1. We coin this regime entropic electrokinetics since the phenomena we identify can only arise due to the spatially varying constriction induced by the geometrical confinement. This variation affects the local spatial distribution of ions, essentially controlled by the interplay between the wall charge and the ion entropy. We will show that the entropic variations in the charge density i...

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“…5 An active soft matter that utilizes chemical potential gradients for motion may be valuable for targeting technologies in drug delivery systems 6 and in the design of active transport systems. 7,8 Moreover, such studies may provide significant insight into the physical chemistry of chemotaxis. Simple mechanisms that generate useful work from chemical potential gradients would be quite useful in the design of simple soft matter with biomimetic characteristics.…”

Section: Introductionmentioning

confidence: 99%

Chemotactic Amoeboid-Like Shape Change of a Vesicle under a pH Gradient

Nawa

Yamamoto

Shioi

2015

Bulletin of the Chemical Society of Japan

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A vesicle that exhibited the extrusion and contraction of a pseudopod-like structure under a pH gradient was studied. The vesicle is composed of oleate and oleic acid, and transforms from a double-spherical shape to a disk-like shape after numerous cyclic shape changes, including the reversal and rotation of the double-spherical vesicle. A pseudopod-like structure is extruded from the vesicle toward a pH gradient, created by NaOH diffusion, and is then contracted. This reversible motion is repeated many times. Notably, NaCl diffusion produces a monotonic and irreversible extrusion. The difference between the two systems could be explained by the cation permeability across the membrane. A mathematical model that accounted for this characteristic reproduced the experimental results semi-quantitatively. Vesicles exhibiting amoeboid-like behaviors, which may be useful in the design of amphiphilic molecular assemblies with biomimetic characteristics, have rarely been reported and are poorly understood. The present study may provide significant insight into the design of such biomimetic vesicles.

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Negative mobility and sorting of colloidal particles

Cited by 58 publications

References 66 publications

Tracer diffusion of hard-sphere binary mixtures under nano-confinement

Tracer diffusion of hard-sphere binary mixtures under nano-confinement

Entropic Electrokinetics: Recirculation, Particle Separation, and Negative Mobility

Chemotactic Amoeboid-Like Shape Change of a Vesicle under a pH Gradient

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