Nanofluidic Osmotic Diodes: Theory and Molecular Dynamics Simulations

Picallo, Clara B.; Gravelle, Simon; Joly, Laurent; Charlaix, Élisabeth; Bocquet, Lydéric

doi:10.1103/physrevlett.111.244501

Cited by 82 publications

(105 citation statements)

References 30 publications

(52 reference statements)

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“…Since there are no heat-selective membranes, thermo-osmosis occurs in open geometries only, where heat and liquid flow in opposite directions along a solid boundary, similarly to electro-osmosis in capillaries or nanofluidic diodes [2]. Water flow due to a temperature gradient was first observed by Derjaguin and Sidorenkov through porous glass from a hot to a cold reservoir [3].…”

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confidence: 99%

Thermo-Osmotic Flow in Thin Films

et al. 2016

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We report on the first micro-scale observation of the velocity field imposed by a non-uniform heat content along the solid/liquid boundary. We determine both radial and vertical velocity components of this thermo-osmotic flow field by tracking single tracer nanoparticles. The measured flow profiles are compared to an approximate analytical theory and to numerical calculations. From the measured slip velocity we deduce the thermo-osmotic coefficient for both bare glass and Pluronic F-127 covered surfaces. The value for Pluronic F-127 agrees well with Soret data for polyethylene glycol, whereas that for glass differs from literature values and indicates the complex boundary layer thermodynamics of glass-water interfaces.

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confidence: 99%

Thermo-Osmotic Flow in Thin Films

et al. 2016

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“…Aqueous electrolytes and model carbon-based materials have already been investigated by molecular simulation in the context of desalination by reverse osmosis [42][43][44] or for nanofluidic osmotic diodes [45]. Molecular simulation provided insights into the structure and dynamics of water and aqueous electrolytes in carbon nanotubes and nanopores [46][47][48].…”

Section: Introductionmentioning

confidence: 99%

Blue Energy and Desalination with Nanoporous Carbon Electrodes: Capacitance from Molecular Simulations to Continuous Models

et al. 2018

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Capacitive mixing (CapMix) and capacitive deionization (CDI) are currently developed as alternatives to membrane-based processes to harvest blue energy-from salinity gradients between river and sea waterand to desalinate water-using charge-discharge cycles of capacitors. Nanoporous electrodes increase the contact area with the electrolyte and hence, in principle, also the performance of the process. However, models to design and optimize devices should be used with caution when the size of the pores becomes comparable to that of ions and water molecules. Here, we address this issue by simulating realistic capacitors based on aqueous electrolytes and nanoporous carbide-derived carbon (CDC) electrodes, accounting for both their complex structure and their polarization by the electrolyte under applied voltage. We compute the capacitance for two salt concentrations and validate our simulations by comparison with cyclic voltammetry experiments. We discuss the predictions of Debye-Hückel and Poisson-Boltzmann theories, as well as modified Donnan models, and we show that the latter can be parametrized using the molecular simulation results at high concentration. This then allows us to extrapolate the capacitance and salt adsorption capacity at lower concentrations, which cannot be simulated, finding a reasonable agreement with the experimental capacitance. We analyze the solvation of ions and their confinement within the electrodes-microscopic properties that are much more difficult to obtain experimentally than the electrochemical response but very important to understand the mechanisms at play. We finally discuss the implications of our findings for CapMix and CDI, both from the modeling point of view and from the use of CDCs in these contexts.

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“…Moreover, the dynamics of suspended particles is strongly affected by the local recirculation of the electrolyte: phenomena such as current inversion particle separation and negative mobility can be attained appropriately tuning the channel shape. Therefore, entropic electrokinetics can be exploited in diverse situations such as low Reynolds fluid mixers [16], electrokinetic batteries [17], microfluidic circuitry [18] and salinity-based energy harvesting devices [19,20] as well as biologically relevant systems such as transpiration in plants [15] or cortical bone fluid flows [14]. In order to characterize this electrokinetic transport regime, we will consider a symmetric, z −z electrolyte solution, in contact with a reservoir of ionic strength ρ 0 z 2 , and filling a varying-section channel of length L and halfaperture h(x) = h 0 − h 1 cos (2πx/L) and whose walls, flat along the z direction, have either a constant surface charge σ or a constant electrostatic potential ζ.…”

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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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Nanofluidic Osmotic Diodes: Theory and Molecular Dynamics Simulations

Cited by 82 publications

References 30 publications

Thermo-Osmotic Flow in Thin Films

Thermo-Osmotic Flow in Thin Films

Blue Energy and Desalination with Nanoporous Carbon Electrodes: Capacitance from Molecular Simulations to Continuous Models

Entropic Electrokinetics: Recirculation, Particle Separation, and Negative Mobility

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