arXiv subjects

Laurent Joly

Publications and source records attributed to Laurent Joly.

At least 19 recordsLinked to original sources

arXiv2025

Molecular insight on ultra-confined ionic transport in wetting films: the key role of friction

Nanofluidic transport is ubiquitous in natural systems from extra-cellular communication in biology to geological phenomena, and promotes the emergence of new technologies such as energy harvesting and water desalination. While experimental access to ultraconfined fluids has advanced rapidly, their behavior challenges conventional theoretical descriptions based on Poisson-Boltzmann theory or the Stokes equation whose possible extension remains an open question. In this work, we use molecular dynamics simulations to investigate ionic transport within wetting films of water confined on silica surfaces down to the sub-nanometer scale. We then analyze these results using a simple one-dimensional theoretical framework. Remarkably, we show that this model remains valid even at confinement close to the molecular scale. Our results reveal that the dynamic of ion plays a key role in ionic transport, through ion adsorption at the water-silica interface. Adsorbed cations do not participate in ionic conduction, but instead generate molecular-scale roughness and transmit additional frictional forces to the substrate. This mechanism produces an apparent viscosity increase in electrostatically driven flows, reaching up to four times the bulk value in the case of potassium. Our findings highlight the critical role of interfacial ion adsorption in nanoscale hydrodynamics and provide new insights for interpreting experiments and designing nanofluidic systems.

cond-mat.soft↗

arXiv2025

The role of confined water in the emergence of electrostatic strong coupling as revealed by nanoseparated charged lipid layers

This study investigates the interplay between Strong Coupling (SC) attraction and hydration repulsion in nanoconfined water between like-charged phospholipid layers. It challenges the assumption that SC attraction requires multivalent counterions by showing that hydration water can enhance electrostatic interactions. We combine reflectivities with numerical simulations to analyze supported phospholipid layers under different relative humidity and surface charge densities. X-ray fluorescence demonstrates that we can control the valence of the associated counterions. Experimental measurement of the water thickness, combined with precise determination of charged surface positions by numerical simulations, enable us to compare our experiments with a theoretical model. It shows that charge-screening by hydration water induces SC attraction, even at moderate surface charge densities with monovalent counterions. Furthermore, hydration repulsion is stronger for DPPS compared to DPPC. These findings offer insights into the forces that control interactions between phospholipid layers and have important implications for biological and colloidal systems.

cond-mat.soft↗

arXiv2025

Dielectric permittivity of water confined in stacks of charged lipid layers: extracting profiles from molecular dynamics simulations using a modified Poisson-Boltzmann equation

Most organic and inorganic surfaces (e.g., glass, nucleic acids or lipid membranes) become charged in aqueous solutions. The resulting ionic distribution induces effective interactions between the charged surfaces. Stacks of like-charged lipid bilayers immersed in multivalent ion solutions exhibit strong coupling (SC) effects, where ion correlations cause counter-intuitive membrane attraction. A similar attraction observed with monovalent ions is explained by SC theory through reduced dielectric permittivity under confinement. To explore this phenomenon, we propose a modified Poisson-Boltzmann (mPB) model with spatially varying dielectric permittivity and explicit Born solvation energy for ions. We use the model to investigate the dielectric permittivity profile of confined water in molecular dynamics simulations of charged lipid layers stacks at varying hydration levels, and compare the results with alternative computational methods. The model captures a sharp decrease in permittivity upon dehydration, converging to a plateau value that we attribute to lipid headgroups. The generic nature of the mPB framework allows application to other systems, such as other biological interfaces or solid walls, provided ions follow Boltzmann statistics. Finally, the increase of the area per lipid in our tension-free simulations of the fluid membranes hints that the permittivity decrease upon dehydration is concomitant with an intermembrane attraction.

cond-mat.soft↗

arXiv2024

Mechanical and thermodynamic routes to the liquid-liquid interfacial tension and mixing free energy by molecular dynamics

In this study, we carried out equilibrium molecular dynamics (EMD) simulations of the liquid-liquid interface between two different Lennard-Jones components with varying miscibility, where we examined the relation between the interfacial tension and isolation free energy using both a mechanical and thermodynamic approach. Using the mechanical approach, we obtained a stress distribution around a quasi-one-dimensional (1D) EMD systems with a flat LL interface. From the stress distribution, we calculated the liquid-liquid interfacial tension based on Bakker's equation, which uses the stress anisotropy around the interface, and measures how it varies with miscibility. The second approach uses thermodynamic integration by enforcing quasi-static isolation of the two liquids to calculate the free energy. This uses the same EMD systems as the mechanical approach, with both extended dry-surface and phantom-wall (PW) schemes applied. When the two components were immiscible, the interfacial tension and isolation free energy were in good agreement, provided all kinetic and interaction contributions were included in the stress. When the components were miscible, the values were significantly different. From the result of PW for the case of completely mixed liquids, the difference was attributed to the additional free energy required to separate the binary mixture into single components against the osmotic pressure prior to the complete detachment of the two components, i.e., the free energy of mixing.

cond-mat.soft↗

arXiv2024

Poisson-Boltzmann formulary: Third edition

The Poisson-Boltzmann (PB) equation provides a mean-field theory of electrolyte solutions at interfaces and in confinement, describing how ions reorganize close to charged surfaces to form the so-called electrical double layer (EDL), with numerous applications ranging from colloid science to biology. This formulary focuses on situations of interest for micro and nanofluidics, and gathers important formulas for the PB description of a Z:Z electrolyte solution inside slit and cylindrical channels. Different approximated solutions (thin EDLs, no co-ion, Debye-Hückel, and homogeneous/parabolic potential limits) and their range of validity are discussed, together with the full solution for the slit channel. Common boundary conditions are presented, the thermodynamics of the EDL is introduced, and an overview of the application of the PB framework to the description of electrokinetic effects is given. Finally, the limits of the PB framework are briefly discussed, and Python scripts to solve the PB equation numerically are provided.

cond-mat.soft↗

arXiv2024

Equilibrium and Non-Equilibrium Molecular Dynamics Simulation of Thermo-Osmosis: Enhanced Effects on Polarized Graphene Surfaces

Thermo-osmotic flows, generated by applying a thermal gradient along a liquid-solid interface, could be harnessed to convert waste heat into electricity. While this phenomenon has been known for almost a century, there is a crucial need to gain a better understanding of the molecular origins of thermo-osmosis. In this paper, we start by detailing the multiple contributions to thermo-osmosis. We then showcase three approaches to compute the thermo-osmotic coefficient using molecular dynamics; a first method based on the computation of the interfacial enthalpy excess and Derjaguin's theoretical framework, a second approach based on the computation of the interfacial entropy excess using the so-called dry-surface method, and a novel non-equilibrium method to compute the thermo-osmotic coefficient in a periodic channel. We show that the three methods align with each other, in particular for smooth surfaces. In addition, for a polarized graphene-water interface, we observe large variations of thermo-osmotic responses, and multiple changes in flow direction with increasing surface charge. Overall, this study showcases the versatility of osmotic flows and calls for experimental investigation of thermo-osmotic behavior in the vicinity of charged surfaces.

cond-mat.soft↗

arXiv2023

Enhanced Interfacial Thermal Conductance between Charged Nanoparticle and Aqueous Electrolyte

Heat transfer through the interface between a metallic nanoparticle and an electrolyte solution, has great importance in a number of applications, ranging from nanoparticle-based cancer treatments to nanofluids and solar energy conversion devices. However, the impact of surface charge and the dissolved ions on heat transfer has been scarcely explored so far. In this study, we compute the interface thermal conductance between hydrophilic and hydrophobic charged gold nanoparticles immersed in an electrolyte using equilibrium molecular dynamics simulations. Compared with an uncharged nanoparticle, we report a threefold increase of the Kapitza conductance for a nanoparticle surface charge +2 e/nm2. This enhancement is shown to be approximately independent of surface wettability, charge spatial distribution, and salt concentration. This allows us to express the Kapitza conductance enhancement in terms of surface charge density on a master curve. Finally, we interpret the increase of the Kapitza conductance as a combined result of a shift in the water density distribution toward the charged nanoparticle and an accumulation of the counter-ions around the nanoparticle surface which increase the Coulombic interaction between the liquid and the charged nanoparticle.

cond-mat.mes-hall↗

arXiv2023

The receding contact line cools down during dynamic wetting

When a contact line (CL) -- where a liquid-vapor interface meets a substrate -- is put into motion, it is well known that the contact angle differs between advancing and receding CLs. Using non-equilibrium molecular dynamics simulations, we reveal another intriguing distinction between advancing and receding CLs: while temperature increases at an advancing CL -- as expected from viscous dissipation, we show that temperature can drop at a receding CL. Detailed quantitative analysis based on the macroscopic energy balance around the dynamic CL showed that the internal energy change of the fluid along the pathline induced a remarkable temperature drop around the receding CL, in a manner similar to latent heat upon phase changes. This result provides new insights for modeling the dynamic CL, and the framework for heat transport analysis introduced here can be applied to a wide range of nanofluidic systems.

physics.flu-dyn↗

arXiv2023

Complex coupling between surface charge and thermo-osmotic phenomena

Thermo-osmotic flows, generated at liquid-solid interfaces by thermal gradients, can be used to produce electric currents from waste heat on charged surfaces. The two key parameters controlling the thermo-osmotic current are the surface charge and the interfacial enthalpy excess due to liquid-solid interactions. While it has been shown that the contribution from water to the enthalpy excess can be crucial, how this contribution is affected by surface charge remained to be understood. Here, we start by discussing how thermo-osmotic flows and induced electric currents are related to the interfacial enthalpy excess. We then use molecular dynamics simulations to investigate the impact of surface charge on the interfacial enthalpy excess, for different distributions of the surface charge, and two different wetting conditions. We observe that surface charge has a strong impact on enthalpy excess, and that the dependence of enthalpy excess on surface charge depends largely on its distribution. In contrast, wetting has a very small impact on the charge-enthalpy coupling. We rationalize the results with simple analytical models, and explore their consequences for thermo-osmotic phenomena. Overall, this work provides guidelines to search for systems providing optimal waste heat recovery performance.

cond-mat.soft↗

arXiv2023

Equilibrium molecular dynamics evaluation of the solid-liquid friction coefficient: role of timescales

Solid-liquid friction plays a key role in nanofluidic systems. Yet, despite decades of method development to quantify solid-liquid friction using molecular dynamics (MD) simulations, an accurate and widely applicable method is still missing. Here, we propose a method to quantify the solid-liquid friction coefficient (FC) from equilibrium MD simulations of a liquid confined between parallel solid walls. In this method, the FC is evaluated by fitting the Green-Kubo (GK) integral of the S-L shear force autocorrelation for the range of time scales where the GK integral slowly decays with time. The fitting function was derived based on the analytical solution considering the hydrodynamic equations in our previous work [H. Oga et al., Phys. Rev. Research 3, L032019 (2021)], assuming that the timescales related to the friction kernel and to the bulk viscous dissipation can be separated. By comparing the results with those of other equilibrium MD-based methods and those of non-equilibrium MD for a Lennard-Jones liquid between flat crystalline walls with different wettability, we show that the FC is extracted with excellent accuracy by the present method, even in wettability regimes where other methods become innacurate. We then show that the method is also applicable to grooved solid walls, for which the GK integral displays a complex behavior at short times. Overall, the present method extracts efficiently the FC for various systems, with easy implementation and low computational cost.

physics.chem-ph↗

arXiv2022

Giant slip length at a supercooled liquid-solid interface

The effect of temperature on friction and slip at the liquid-solid interface has attracted attention over the last twenty years, both numerically and experimentally. However, the role of temperature on slip close to the glass transition has been less explored. Here, we use molecular dynamics to simulate a bi-disperse atomic fluid, which can remain liquid below its melting point (supercooled state), to study the effect of temperature on friction and slip length between the liquid and a smooth apolar wall, in a broad range of temperatures. At high temperatures, an Arrhenius law fits well the temperature dependence of viscosity, friction and slip length. In contrast, when the fluid is supercooled, the viscosity becomes super-Arrhenian, while interfacial friction can remain Arrhenian or even drastically decrease when lowering the temperature, resulting in a massive increase of the slip length. We rationalize the observed superlubricity by the surface crystallization of the fluid, and the incommensurability between the structures of the fluid interfacial layer and of the wall. This study calls for experimental investigation of the slip length of supercooled liquids on low surface energy solids.

cond-mat.soft↗

arXiv2022

Microscopic origins of the viscosity of a Lennard-Jones liquid

Unlike crystalline solids or ideal gases, transport properties remain difficult to describe from a microscopic point of view in liquids, whose dynamics result from complex energetic and entropic contributions at the atomic scale. Two scenarios are generally proposed: one represents the dynamics in a fluid as a series of energy barrier crossings, leading to Arrhenius-like laws, while the other assumes that atoms rearrange themselves by collisions, as exemplified by the free volume model. To assess the validity of these two views, we computed, using molecular dynamics simulations, the transport properties of the Lennard-Jones fluid and tested to what extent the Arrhenius equation and the free volume model describe the temperature dependence of the viscosity and of the diffusion coefficient at fixed pressure. Although both models reproduce the simulation results over a wide range of pressure and temperature covering the liquid and supercritical states of the Lennard-Jones fluid, we found that the parameters of the free volume model can be estimated directly from local structural parameters, also obtained in the simulations. This consistency of the results gives more credibility to the free volume description of transport properties in liquids.

cond-mat.soft↗

arXiv2022

Chapter: Energy conversion at water-solid interfaces using electrokinetic effects

Our Society is in high need of alternatives to fossil fuels. Nanoporous systems filled with aqueous electrolytes show great promises for harvesting the osmotic energy of sea water or waste heat. At the core of energy conversion in such nanofluidic systems lie the so-called electrokinetic effects, coupling thermodynamic gradients and fluxes of different types (hydrodynamical, electrical, chemical, thermal) at electrified water-solid interfaces. This chapter starts by introducing the framework of linear irreversible thermodynamics, and how the latter can be used to describe the direct and coupled responses of a fluidic system, providing general relations between the different response coefficients. The chapter then focuses on the so-called osmotic flows, generated by non-hydrodynamic actuation at liquid-solid interfaces, and illustrate how the induced fluxes can be related to the microscopic properties of the water-solid interface. Finally, the chapter moves to electricity production from non-electric actuation, and discusses in particular the performance of nanofluidic systems for the harvesting of osmotic energy and waste heat.

physics.flu-dyn↗

arXiv2021

Connection between water's dynamical and structural properties: insights from ab initio simulations

Among all fluids, water has always been of special concern for scientists from a broad variety of research fields due to its rich behavior. In particular, some questions remain unanswered nowadays concerning the temperature dependence of bulk and interfacial transport properties of supercooled and liquid water, e.g. regarding the fundamentals of the violation of the Stokes-Einstein relation in the supercooled regime or the subtle relation between structure and dynamical properties. Here we investigated the temperature dependence of the bulk transport properties from ab initio molecular dynamics based on density functional theory, down to the supercooled regime. We determined from a selection of functionals, that SCAN better describes the experimental viscosity and self-diffusion coefficient, although we found disagreements at the lowest temperatures. For a limited set of temperatures, we also explored the role of nuclear quantum effects on water dynamics using ab initio molecular dynamics that has been accelerated via a recently introduced machine learning approach. We then investigated the molecular mechanisms underlying the different functionals performance and assessed the validity of the Stokes-Einstein relation. We also explored the connection between structural properties and the transport coefficients, verifying the validity of the excess entropy scaling relations for all the functionals. These results pave the way to predict the transport coefficients from the radial distribution function, helping to develop better functionals. On this line, they indicate the importance of describing the long-range features of the radial distribution function.

physics.chem-ph↗

arXiv2021

Electro-osmosis at surfactant-laden liquid-gas interfaces: beyond standard models

Electro-osmosis (EO) is a powerful tool to manipulate liquids in micro and nanofluidic systems. While EO has been studied extensively at liquid-solid interfaces, the case of liquid-vapor interfaces, found e.g. in foam films and bubbles, remains to be explored. Here we perform molecular dynamics (MD) simulations of EO in a film of aqueous electrolyte covered with fluid layers of ionic surfactants and surrounded by gas. Following the experimental procedure, we compute the zeta potential from the EO velocity, defined as the velocity difference between the middle of the liquid film and the surrounding gas. We show that the zeta potential can be smaller or larger than existing predictions depending on the surfactant coverage. We explain the failure of previous descriptions by the fact that surfactants and bound ions move as rigid bodies and do not transmit the electric driving force to the liquid locally. Considering the reciprocal streaming current effect, we then develop an extended model, which can be used to predict the experimental zeta potential of surfactant-laden liquid-gas interfaces.

cond-mat.soft↗

arXiv2021

Fast and Versatile Thermo-osmotic Flows with a Pinch of Salt

Thermo-osmotic flows - flows generated in micro and nanofluidic systems by thermal gradients - could provide an alternative approach to harvest waste heat. However, such use would require massive thermo-osmotic flows, which are up to now only predicted for special and expensive materials. There is thus an urgent need to design affordable nanofluidic systems displaying large thermo-osmotic coefficients. In this paper we propose a general model for thermo-osmosis of aqueous electrolytes in charged nanofluidic channels, taking into account hydrodynamic slip, together with the different solvent and solute contributions to the thermo-osmotic response. We apply this model to a wide range of systems, by studying the effect of wetting, salt type and concentration, and surface charge. We show that intense thermo-osmotic flows can be generated using slipping charged surfaces. We also predict for intermediate wettings a transition from a thermophobic to a thermophilic behavior depending on the surface charge and salt concentration. Overall, this theoretical framework opens an avenue for controlling and manipulating thermally induced flows with common charged surfaces and a pinch of salt.

physics.flu-dyn↗

arXiv2021

Osmotic transport at the aqueous graphene and hBN interfaces: scaling laws from a unified, first principles description

Osmotic transport in nanoconfined aqueous electrolytes provides new venues for water desalination and "blue energy" harvesting; the osmotic response of nanofluidic systems is controlled by the interfacial structure of water and electrolyte solutions in the so-called electrical double layer (EDL), but a molecular-level picture of the EDL is to a large extent still lacking. Particularly, the role of the electronic structure has not been considered in the description of electrolyte/surface interactions. Here, we report enhanced sampling simulations based on ab initio molecular dynamics, aiming at unravelling the free energy of prototypical ions adsorbed at the aqueous graphene and hBN interfaces, and its consequences on nanofluidic osmotic transport. Specifically, we predicted the zeta potential, the diffusio-osmotic mobility and the diffusio-osmotic conductivity for a wide range of salt concentrations from the ab initio water and ion spatial distributions through an analytical framework based on Stokes equation and a modified Poisson-Boltzmann equation. We observed concentration-dependent scaling laws, together with dramatic differences in osmotic transport between the two interfaces, including diffusio-osmotic flow and current reversal on hBN, but not on graphene. We could rationalize the results for the three osmotic responses with a simple model based on characteristic length scales for ion and water adsorption at the surface, which are quite different on graphene and on hBN. Our work provides first principles insights into the structure and osmotic transport of aqueous electrolytes on two-dimensional materials and explores new pathways for efficient water desalination and osmotic energy conversion.

physics.chem-ph↗

arXiv2021

Enhanced local viscosity around colloidal nanoparticles probed by Equilibrium Molecular Dynamics Simulations

Nanofluids; dispersions of nanometer-sized particles in a liquid medium; have been proposed for a wide variety of thermal management applications. It is known that a solid-like nanolayer of liquid of typical thickness 0.5-1 nm surrounding the colloidal nanoparticles can act as a thermal bridge between the nanoparticle and the bulk liquid. Yet, its effect on the nanofluid viscosity has not been elucidated so far. In this article, we compute the local viscosity of the nanolayer using equilibrium molecular dynamics based on the Green-Kubo formula. We first assess the validity of the method to predict the viscosity locally. We apply this methodology to the calculation of the local viscosity in the immediate vicinity of a metallic nanoparticle for a wide range of solid-liquid interaction strength, where a nanolayer of thickness 1 nm is observed as a result of the interaction with the nanoparticle. The viscosity of the nanolayer, which is found to be higher than its corresponding bulk value, is directly dependent on the solid-liquid interaction strength. We discuss the origin of this viscosity enhancement and show that the liquid density increment alone cannot explain the values of the viscosity observed. Rather, we suggest that the solid-like structure of the distribution of the liquid atoms in the vicinity of the nanoparticle contributes to the nanolayer viscosity enhancement. Finally, we observe a failure of the Stokes-Einstein relation between viscosity and diffusion close to the wall, depending on the liquid-solid interaction strength, which we rationalize in terms of hydrodynamic slip.

cond-mat.soft↗