Nanofluidics has emerged recently in the footsteps of microfluidics, following the quest of scale reduction inherent to nanotechnologies. By definition, nanofluidics explores transport phenomena of fluids at the nanometer scales. Why is the nanometer scale specific ? What fluid properties are probed at nanometric scales ? In other words, why 'nanofluidics' deserves its own brand name ? In this critical review, we will explore the vast manifold of length scales emerging for the fluid behavior at the nanoscales, as well as the associated mechanisms and corresponding applications. We will in particular explore the interplay between bulk and interface phenomena. The limit of validity of the continuum approaches will be discussed, as well as the numerous surface induced effects occuring at these scales, from hydrodynamic slippage to the various electro-kinetic phenomena originating from the couplings between hydrodynamics and electrostatics. An enlightening analogy between ion transport in nanochannels and transport in doped semi-conductors will be discussed.
Nanofluidics is an emerging field offering innovative solutions for energy harvesting and desalination. The efficiency of these applications depends strongly on liquid-solid slip, arising from a favorable ratio between viscosity and interfacial friction. Using molecular dynamics simulations, we show that wall slip increases strongly when water is cooled below its melting point. For water on graphene, the slip length is multiplied by up to a factor of five and reaches $230$nm at the lowest simulated temperature, $T \sim 225$K; experiments in nanopores can reach much lower temperatures and could…
Fluctuation-induced and quantum effects in nanofluidic transport
Laboratoire de Physique de l’École Normale Supérieure（巴黎高等师范学院物理实验室）；The Quantum Plumbing Lab, École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院量子管道实验室）；Institute of Science and Technology Austria (ISTA)（奥地利科学技术研究所）
We prove three exact sum rules that relate the polarization of active Brownian particles to their one-body current: (i) The total polarization vanishes, provided that there is no net flux through the boundaries, (ii) at any planar wall the polarization is determined by the magnitude of the bulk current, and (iii) the total interface polarization between phase-separated fluid states is rigorously determined by the gas-liquid current difference. This result precludes the influence of the total interface polarization on active bulk coexistence and questions the proposed coupling of interface to b…
Using concepts from perturbation and local molecular field theories of liquids we divide the potential of the SPC/E water model into short and long ranged parts. The short ranged parts define a minimal reference network model that captures very well the structure of the local hydrogen bond network in bulk water while ignoring effects of the remaining long ranged interactions. This deconstruction can provide insight into the different roles that the local hydrogen bond network, dispersion forces, and long ranged dipolar interactions play in determining a variety of properties of SPC/E and relat…
From bulk to interface dynamics, in and out of equilibrium
Laboratoire Matière et Systèmes Complexes, Université Paris Cité & CNRS (UMR 7057)（复杂物质与系统实验室，巴黎西岱大学及法国国家科学研究中心）；Department of Physics, Massachussets Institute of Technology（麻省理工学院物理系）；Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所）
Hollow cylinders with a diameter in the nanometer range are carving out prime positions in nanoscience. Thanks to their physico-chemical properties, they could be key elements for next-generation nanofluidics devices, for selective molecular sieving, energy conversion or as catalytic nanoreactors. Several difficult problems such as fine diameter and interface control are solved for imogolite nanotubes. This chapter will present an overview of this unique class of clay nanotubes, from their geological occurrence to their synthesis and their applications. In particular, emphasis will be put on p…
Electrokinetic effects offer a method of choice to control flows in micro and nanofluidic systems. While a rather clear picture of these phenomena exists now for the liquid-solid interfaces, the case of liquid-air interfaces remains largely unexplored. Here we investigate at the molecular level electrokinetic transport in a liquid film covered with ionic surfactants. We find that the zeta potential, quantifying the amplitude of electrokinetic effects, depends on the surfactant coverage in an unexpected way. First, it increases upon lowering surfactant coverage from saturation. Second, it does …
Anions generally associate more favorably with the air-water interface than cations. In addition to solute size and polarizability, the intrinsic structure of the unperturbed interface has been discussed as an important contributor to this bias. Here we assess quantitatively the role that intrinsic charge asymmetry of water's surface plays in ion adsorption, using computer simulations to compare model solutes of various size and charge. In doing so, we also evaluate the degree to which linear response theory for solvent polarization is a reasonable approach for comparing the thermodynamics of …
Simulations of liquid-gas systems with extended interfaces are observed to fail to give accurate results for two reasons: the interface can get ``stuck'' on the lattice or a density overshoot develops around the interface. In the first case the bulk densities can take a range of values, dependent on the initial conditions. In the second case inaccurate bulk densities are found. In this communication we derive the minimum interface width required for the accurate simulation of liquid gas systems with a diffuse interface. We demonstrate this criterion for lattice Boltzmann simulations of a van d…
The behavior at the air/water interface of multilamellar tubes made of the ethanolamine salt of the 12-hydroxy stearic acid as a function of the temperature has been investigated using Neutron Reflectivity. Those tubes are known to exhibit a temperature tunable diameter in the bulk. We have observed multilamellar tubes adsorbed at the air/water interface by specular neutron reflectivity. Interestingly, at the interface, the adsorbed tubes exhibit the same behavior than in the bulk upon heating. There is however a peculiar behavior at around 50\degree for which the increase of the diameter of t…
Elongated active units cannot spontaneously break rotation symmetry in bulk fluids to form nematic or polar phases. This has led to the image of active suspensions as spontaneously evolving, spatiotemporally chaotic fluids. In contrast, I show that bulk active fluids have stable active nematic and polar states at fluid-fluid or fluid-air interfaces. The active flow-mediated long-range interactions that destroy the ordered phase in bulk, lead to long-range order at the interface. The active fluids have a surface ordering transition and form states with quiescent, ordered surfaces and a chaotic …
Why Some Metal Ions Spontaneously Form Nanoparticles in Water Microdroplets? Disentangling the Contributions of Air-Water Interface and Bulk Redox Chemistry
Characteristics of relaxed density profile and conformation of polymer chains are studied by a Monte Carlo simulation on a discrete lattice in three dimensions using different segmental (kink-jump $K$, crank-shaft $C$, reptation $R$) dynamics. Three distinct density regimes, substrate, bulk, and interface, are identified. With the $KC$ segmental dynamics we find that the substrate coverage grows with a power-law, $d_s \propto t^γ$ with a field dependent nonuniversal exponent $γ= 0.23 + 0.7 E$. The bulk volume fraction $d_b$ and the substrate polymer density ($d_s$) increases exponentially with…
We consider interfacial phenomena accompanying bulk quantum phase transitions in presence of surface fields. On general grounds we argue that the surface contribution to the system free energy involves a line of singularities characteristic of an interfacial phase transition, occurring below the bulk transition temperature T_c down to T=0. This implies the occurrence of an interfacial quantum critical regime extending into finite temperatures and located within the portion of the phase diagram where the bulk is ordered. Even in situations, where the bulk order sets in discontinuously at T=0, t…
Interfaces between demixed fluid phases of binary mixtures of hard platelets are investigated using density-functional theory. The corresponding excess free energy functional is calculated within a fundamental measure theory adapted to the Zwanzig model, in which the orientations of the particles of rectangular shape are restricted to three orthogonal orientations. Density and orientational order parameter profiles at interfaces between coexisting phases as well as the interfacial tension are determined. A density inversion, oscillatory density profiles, and a Fisher-Widom line have been found…
Large-scale simulations of thermal welding of polymers are performed to investigate the rise of mechanical strength at the polymer-polymer interface with the welding time. The welding process is in the core of integrating polymeric elements into devices as well as in thermal induced healing of polymers; processes that require development of interfacial strength equal to that of the bulk. Our simulations show that the interfacial strength saturates at the bulk shear strength much before polymers diffuse by their radius of gyration. Along with the strength increase, the dominant failure mode cha…
Total Internal Reflection (TIR) is used to probe the molecular organization at the surface of a tilted chiral smectic liquid crystal at temperatures in the vicinity of the bulk antiferroelectric-ferroelectric phase transition. Data are interpreted using an exact analytical solution of a real model for ferroelectric order at the surface. In the mixture T3, ferroelectric surface order is expelled with the bulk ferroelectric-antiferroelectric transition. The conditions for ferroelectric order at the surface of an antiferroelectric bulk are presented.
Screening is one of the most important concepts in the study of charged systems. Near a dielectric interface, the ion distribution in a salt solution can be highly nonuniform. Here, we develop a theory that self-consistently treats the inhomogeneous screening effects. At higher concentrations when the bulk Debye screening length is comparable to the Bjerrum length, the double layer structure and interfacial properties are significantly affected by the inhomogeneous screening. In particular, the depletion zone is considerably wider than that predicted by the bulk screening approximation or the …
The influence of substrate treatment with self-assembled monolayers and thermal annealing was analysed by electrical and structural measurements on field-effect transistors (FETs) and metal-insulator-semiconductor (MIS) diodes using poly(3-hexylthiophene) (P3HT) as a semiconducting polymer and Si/SiO2 wafers as a substrate. It is found that surface treatment using silanising agents like hexamethyldisilazane (HMDS) and octadecyltrichlorosi-lane (OTS) can increase the field-effect mobility by up to a factor of 50, reaching values in saturation of more than 4E-2 cm^2/Vs at room temperature. While…
The structure of liquid water in the proximity of an interface can deviate significantly from that of bulk water, with surface-induced structural perturbations typically converging to bulk values at about ~1 nm from the interface. While these structural changes are well established it is, in contrast, less clear how an interface perturbs the dynamics of water molecules within the liquid. Here, through an extensive set of molecular dynamics simulations of supercooled bulk and interfacial water films and nano-droplets, we observe the formation of persistent, spatially extended dynamical domains …
Large-scale molecular simulations are performed to investigate tensile failure of polymer interfaces as a function of welding time $t$. Changes in the tensile stress, mode of failure and interfacial fracture energy $G_I$ are correlated to changes in the interfacial entanglements as determined from Primitive Path Analysis. Bulk polymers fail through craze formation, followed by craze breakdown through chain scission. At small $t$ welded interfaces are not strong enough to support craze formation and fail at small strains through chain pullout at the interface. Once chains have formed an average…
We consider the problem of boiling of the direct contact of two immiscible liquids. An intense vapour formation at such a direct contact is possible below the bulk boiling points of both components, meaning an effective decrease of the boiling temperature of the system. Although the phenomenon is known in science and widely employed in technology, the direct contact boiling process was thoroughly studied (both experimentally and theoretically) only for the case where one of liquids is becoming heated above its bulk boiling point. On the contrary, we address the case where both liquids remain b…
To comprehend the complexities of the ice-water interface, we perform a study that attempts to correlate the altered dynamics of water to its perturbed structure at, and due to, the interface. The deviation from bulk values of structural and dynamical quantities at the interface are obtained by computer simulations. Water molecules are found to get exchanged between the ice-like and water-like domains of the interface with a time scale of the order of ~10 ps. To investigate the effect of interfaces in general, we study three other systems, namely (i) water between two hydrophobic nano-slabs, (…
We investigate the solvent mediated interactions between nanoparticles adsorbed at a liquid-vapor interface in comparison to the solvent mediated interactions in the bulk liquid and vapor phases of a Lennard-Jones solvent. Molecular dynamics simulation data for the latter are in good agreement with results from integral equations in the reference functional approximation and a simple geometric approximation. Simulation results for the solvent mediated interactions at the interface differ markedly from the interactions of the particles in the corresponding bulk phases. We find that at short int…
Ionic liquid crystals (ILCs) are anisotropic mesogenic molecules which additionally carry charges. This combination gives rise to a complex interplay of the underlying (anisotropic) contributions to the pair interactions. It promises interesting and distinctive structural and orientational properties to arise in systems of ILCs, combining properties of liquid crystals and ionic liquids. While previous theoretical studies have focused on the phase behavior of ILCs and the structure of the respective bulk phases, in the present study we provide new results, obtained within density functional the…
A general theory of thermodynamically consistent biomechanical--biochemical growth in a body, considering mass addition in the bulk and at an incoherent interface, is developed. The incoherency arises due to incompatibility of growth and elastic distortion tensors at the interface. The incoherent interface therefore acts as an additional source of internal stress besides allowing for rich growth kinematics. All the biochemicals in the model are essentially represented by nutrient concentration fields, in the bulk and at the interface. A nutrient balance law is postulated which, combined with m…
Protein adsorption at the solid-liquid interface is an important phenomenon that often can be observed as a first step in biological processes. Despite its inherent importance, still relatively little is known about the underlying microscopic mechanisms. Here, using multivalent ions, we demonstrate the control of the interactions and the corresponding adsorption of net-negatively charged proteins (bovine serum albumin) at a solid-liquid interface. This is demonstrated by ellipsometry and corroborated by neutron reflectivity and quartz-crystal microbalance experiments. We show that the reentran…
The possibility to extract properties of an interface between two immiscible liquids, e.g., electrolyte solutions or polyelectrolyte multilayers, by means of impedance spectroscopy is investigated theoretically within a dynamic density functional theory which is equivalent to the Nernst-Planck-Poisson theory. A novel approach based on a two-step fitting procedure of an equivalent circuit to impedance spectra is proposed which allows to uniquely separate bulk and interfacial elements. Moreover, the proposed method avoids overfitting of the bulk properties of the two liquids in contact and under…
This paper is aiming at presenting some relevant contributions of Jean-Pierre Badiali during the first ten years of his growing scientific activity. This presentation does not contain new materials but is based on a number of selected papers published in the seventies, a part of them written in French. The presentation is organized around three points. The first point, corresponding to his PhD thesis, is concerned with the study of ion-solvent and ion-ion interactions in a solution using complex dielectric permittivity measurements in the Hertzian and microwave frequency range. The second one …
Nonequilibrium molecular dynamics simulations are used to study the shear thinning behavior of immiscible symmetric polymer blends. The phase separated polymers are subjected to a simple shear flow imposed by moving a wall parallel to the fluid-fluid interface. The viscosity begins to shear thin at much lower rates in the bulk than at the interface. The entire shear rate dependence of the interfacial viscosity is consistent with a shorter effective chain length $s^*$ that also describes the width of the interface. This $s^*$ is independent of chain length $N$ and is a function only of the degr…
