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New publication in Phys. of. Fluids on microscopic insights of surface tension of water confined in CNT - Molecular-driven extreme surface tension of water in carbon nanotubes -
Abstract: At the nanoscale when the system shrinks down, interfacial interactions govern fluid behavior, often defying bulk expectations. Using classical molecular simulations, we directly calculate the surface tension of water confined in carbon nanotubes (CNTs). Unlike planar interfaces, where confinement enhances surface tension monotonically, cylindrical confinement reveals a striking non-monotonic trend. In narrow CNTs, strong wa- ter–carbon repulsion yields giant surface tensions exceeding twice the bulk value. At a critical pore radius, water organizes into ordered hexagonal and pentagonal networks, driving an unexpected collapse—and even negative values—of the surface tension. These behaviors were also recovered for confined methane and for a different water model, further supporting the confinement effect on surface tension. Comparison with thermo- dynamic models, including Gibbs and Tolman representations as well as the recently introduced concepts of differential and integral surface tension, highlights their limitations in capturing the pore-radius dependence and the anomalous values observed. We establish water–carbon repulsion, curvature, and molecular structur- ing as the key determinants of confined-water surface tension, with broad implications for nanofluidics and interfacial thermodynamics.
New publication in Phys. Rev. E on the role of confinement and excluded effects on surface tension of water in CNT - A Surface tension enhancement in nanoconfined water: The role of confinement and excluded volume effects - Abstract: In this work, the surface tension (γ) of nanoconfined water between planar interfaces was evaluated using atomistic simulations combined with the test-area method. To elucidate the role of spatial restriction, two types of confinement were considered: solid and liquid. In the case of solid surfaces, a strong increase in surface tension was observed compared to the unconfined case—i.e., water in contact with a single interface. In contrast, no significant change in surface tension was found under hydrophobic liquid confinement, indicating that spatial restriction alone does not fully account for the increase in γ. Our results demonstrate that the enhancement of surface tension arises from a synergistic interplay between confinement and excluded volume effects, amplified by a lack of miscibility between the two phases. These findings highlight the importance of interfacial structure and phase compatibility in determining the interfacial properties of confined fluids.
New publication in MRS advances on MOF modelling in oosmotic statistical ensemble - A discussion on the dynamical ergodicity/memory (breakdown) in hybrid MD/GCMC simulation of adsorption-induced transitions in metal–organic frameworks Abstract - Hybrid molecular dynamics/grand canonical Monte Carlo (MD/GCMC) simulations are increasingly employed to study adsorption-induced structural transitions in flexible metal–organic frameworks (MOFs). While these approaches can capture guest-triggered transformations such as breathing phenomenon or negative gas adsorption, their fundamental validity hinges on ergodicity—a requirement rarely scrutinized. Here, I critically examine the ergodic properties of MD/GCMC and related hybrid schemes. I show that although such methods preserve statistical ergodicity by design, they break dynamical ergodicity due to discontinuities introduced by particle insertion and deletion moves. This breakdown has consequences, including dependence on initial conditions or biased sampling, and loss of physical interpretability of time correlations. I compare MD/GCMC, osmotic molecular dynamics, and hybrid osmotic Monte Carlo, and identify the conditions under which ergodicity is breakdown. This analysis establishes criteria for the reliable use of hybrid simulations and highlights the need for physically consistent alternatives that explicitly couple MOFs to real gas reservoirs.
Recently, I made a short video with Morgan Lechat and CNRS Villejuif about desalination using artificial channels, in the context of the ANR BIOWATER project, in partnership with ICGM, IEM, IPR, and ISCR.
A new result on dielectric permittivity: Fumagalli et al.’s group has just demonstrated the existence of a giant dielectric permittivity of water under nanometric confinement (≈ 1000 ± 350) [Nature, 2025, In-plane dielectric constant and conductivity of confined water]. More precisely, this concerns the axial component, while the orthogonal contribution lies well below the bulk value. This experimental result therefore confirms the findings that we obtained — about ten years earlier — through molecular simulations (Superpermittivity of nanoconfined water, JCP, 2012; Anomalous Dielectric Behavior of Nanoconfined Electrolytic Solutions, PRL, 2012; Calculation of Local Dielectric Permittivity of Confined Liquids from Spatial Dipolar Correlations, EPL, 2012; …). It shows that, when properly used — classical molecular simulation can be a remarkably powerful predictive tool.
New publication in J. Chem. Phys. with internships for third-year Physics students (M. Arribard, G. Makaya & L. Tauv): Modeling Surface and Line Tensions of Nanoconfined Water using a Single Atomistic Simulation
New publication in J. Chem. Phys. with internships for third-year Physics students (M. Arribard, G. Makaya & L. Tauv): Modeling Surface and Line Tensions of Nanoconfined Water using a Single Atomistic Simulation
An interesting review in Nature Review Physics
Atomistic computing of the solid–fluid surface free energy and tension
Nat. Rev. Phys., 2025
Visit of Hoachen Zhu (2025 July), a colleague from Tongji University, to ICMPE
for a new project on heavy metal extraction by reverse osmosis
End of internships for third-year Physics students (M. Arribard, G. Makaya & L. Tauv) at ICMPE and preparation for their internship defense
New paper wth Morshed Mahmud as main investigator
(Deciphering the role of water in ethanol uptake within PIM-1 membranes, M. Mahmud, B. van der Bruggen, A. Ghoufi, A. Szymczyk, Journal of Membrane Science, 733, 124314, 2025)
Molecular interactions between solvents and membranes are a key factor for understanding the performance of organic solvent nanofiltration membranes. In this study, the behavior of pure water and ethanol as well as their mixtures confined in a PIM-1 membrane was investigated by means of molecular dynamics simulations. The nitrogen atom of PIM-1 was found to be the preferential interaction site for the various systems. The uptake of pure water and ethanol by the PIM-1 membrane was found similar. However, the ethanol uptake greatly increased in the presence of water, whatever the composition of the mixture. This intriguing behavior was further explained by molecular simulations, which revealed that water molecules create molecular bridges between the PIM-1 nitrogen atoms and ethanol molecules via hydrogen bonds, thus providing additional adsorption sites for ethanol. Simulations also highlighted that the translational dynamics of ethanol in the PIM-1 membrane was slowed down more than that of water due to the larger molecular size of ethanol (greater degree of confinement) and that it was more strongly impacted by the membrane confinement than by water-ethanol interactions. The same conclusion was drawn for rotational dynamics. However, for confined mixtures, the rotational dynamics of confined water were found to be imposed by ethanol, with similar relaxation times for both kinds of dipoles.
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