Posted Jul 10, 2023
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-[{"authors":null,"categories":null,"content":"About me\nI am a CNRS researcher at LIPhy in Grenoble, France. I use molecular simulations to study fluids at interfaces and soft matter systems.\nOpen source and open data\nI share all the codes developed as part of my research as open source, see for instance:\nmy Github repository containing molecular simulation scripts and data, NMRforMD, a Python script for calculating hydrogen NMR relaxation rates from molecular dynamics simulations, In parallel to my open-source projects, I have been involved in the development of MAICoS, a Python toolkit for analyzing confined molecular simulations.\nOutreach\nIn parallel to my research activities, I am developing several outreach projects, including:\nthe LAMMPS tutorials webpage and its associated repositories, the GROMACS tutorials page, a gallery of animations and molecular art. ","date":-62135596800,"expirydate":-62135596800,"kind":"term","lang":"en","lastmod":-62135596800,"objectID":"2525497d367e79493fd32b198b28f040","permalink":"","publishdate":"0001-01-01T00:00:00Z","relpermalink":"","section":"authors","summary":"About me\nI am a CNRS researcher at LIPhy in Grenoble, France. I use molecular simulations to study fluids at interfaces and soft matter systems.\nOpen source and open data","tags":null,"title":"Simon Gravelle","type":"authors"},{"authors":[],"categories":null,"content":" Click on the Slides button above to view the built-in slides feature. Slides can be added in a few ways:\nCreate slides using Wowchemy’s Slides feature and link using slides parameter in the front matter of the talk file Upload an existing slide deck to static/ and link using url_slides parameter in the front matter of the talk file Embed your slides (e.g. Google Slides) or presentation video on this page using shortcodes. Further event details, including page elements such as image galleries, can be added to the body of this page.\n","date":1906549200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1906549200,"objectID":"a8edef490afe42206247b6ac05657af0","permalink":"https://simongravelle.github.io/talk/example-talk.html","publishdate":"2017-01-01T00:00:00Z","relpermalink":"/talk/example-talk.html","section":"event","summary":"An example talk using Wowchemy's Markdown slides feature.","tags":[],"title":"Example Talk","type":"event"},{"authors":null,"categories":null,"content":"","date":1697328e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1697328e3,"objectID":"01b5f0738efb9f4ac8fc3559d8fd6ca8","permalink":"https://simongravelle.github.io/gallery/graphene.html","publishdate":"2023-10-15T00:00:00Z","relpermalink":"/gallery/graphene.html","section":"gallery","summary":"","tags":null,"title":"Wave in graphene","type":"gallery"},{"authors":null,"categories":null,"content":"","date":1696896e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1696896e3,"objectID":"e9441bf62787bdcbbf4f79a8c7ec421a","permalink":"https://simongravelle.github.io/gallery/fullrene.html","publishdate":"2023-10-10T00:00:00Z","relpermalink":"/gallery/fullrene.html","section":"gallery","summary":"","tags":null,"title":"Fullerene collision","type":"gallery"},{"authors":null,"categories":null,"content":"","date":1696464e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1696464e3,"objectID":"a4afb40bb80bd0d47a437bd23e31f11e","permalink":"https://simongravelle.github.io/gallery/ring.html","publishdate":"2023-10-05T00:00:00Z","relpermalink":"/gallery/ring.html","section":"gallery","summary":"","tags":null,"title":"The molecular ring","type":"gallery"},{"authors":null,"categories":null,"content":"Update. The offer has now expired, and the selection process has moved to the next step.\nScope. With the goal to reach carbon neutrality by 2050, direct air capture (DAC) of CO2 from wet flue gases is one brick of the carbon mitigation strategy – especially with the next generation of solid porous sorbents based on Metal-Organic Frameworks (MOF). While thermodynamics of the CO2 capture is well documented in the literature, little is known about molecular diffusion and transport properties in MOF angstropores (in particular, in the presence of environmental humidity). Also, diffusion through pore scales of the applicative sorbing medium, ranging from nanopores (pore diameter ~nm) to macropores (\u0026gt; 50 nm) and beyond remain open. In order to fill the gap and gain insight into multiscale transport properties and try to figure CO2 capture optimization through MOF based sorbents, we ambition to develop a multiscale approach based on a lattice model fed by molecular simulations.\nIn more detail, the objective of this PhD proposal is two-fold. i. Using molecular simulations [e.g. Magnin et al. J. Phys. Chem. C 2022], we aim to unravel the molecular phenomena that govern the thermodynamic and kinetic mechanisms when capturing CO2 using a multi-scale porous material. With this first aspect, we aim to rationalize the use of nanoporous materials for practical engineering processes by developing a robust and general methodology to link physico-chemical properties at different scales. ii. Using a bottom-up strategy, we will upscale the results obtained using atomistic simulations to mimic phase separation and transport of CO2/N2/H2O mixtures at the macroscale. To do so, a simple yet realistic lattice model [Botan et al. Phys. Rev. E 2015], which can be seen as a pore network model accounting for the change of the local thermodynamic/transport properties in a kinetic engineering process (e.g. Pressure Swing Adsorption), will be used.\nPotential candidate. The PhD candidate should have a background in physics, physical chemistry/chemical physics or materials science. He/she should also have some experience in scientific programming and a background in statistical mechanics (including if possible Monte Carlo or/and Molecular Dynamics).\nPractical aspects. The position is available starting January 2024 and lasts for 36 months. The PhD student will work under the supervision of Benoit Coasne/Simon Gravelle (LIPhy, Grenoble) and Yann Magnin (CSTJF, Pau). He/she will be located at LIPhy in Grenoble, France but several short stays in CSTJF in Pau, France will be planned. Applicants should provide a CV, a letter of motivation and the names and email addresses of 2 or 3 references to:\nYann Magnin (yann.magnin at totalenergies.com) Benoit Coasne (benoit.coasne at univ-grenoble-alpes.fr) Simon Gravelle (simon.gravelle at univ-grenoble-alpes.fr) More information:\nhttps://benoitcoasne.github.io/ (Coasne’s research group website) https://www.yann-magnin.fr/ (research website) ","date":1688947200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1688947200,"objectID":"bcbcff3cc776cd413546f797aaac134f","permalink":"https://simongravelle.github.io/news/2023-phd-offer.html","publishdate":"2023-07-10T00:00:00Z","relpermalink":"/news/2023-phd-offer.html","section":"news","summary":"CO2 Capture Using Nanoporous Adsorbents -- A Multiscale Numerical Approach From Molecular Aspects to the Engineering Scale","tags":["Job"],"title":"PhD Position Available in LIPhy (Filled)","type":"news"},{"authors":null,"categories":null,"content":"In the continuity of my MSCA fellowship, I’ve been hired by the French CNRS (Section 11) as a tenured full time researcher at LIPhy (UGA).\n","date":1687996800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1687996800,"objectID":"d9cfc7a9d756d2a010e13ea6d11dcf56","permalink":"https://simongravelle.github.io/news/2023-cnrs-start.html","publishdate":"2023-06-29T00:00:00Z","relpermalink":"/news/2023-cnrs-start.html","section":"news","summary":"I will be mainly working on the separation of fluid mixture using soft matter membrane, in LiPhy, Grenoble.","tags":["Personal"],"title":"I have obtained a position at French CNRS","type":"news"},{"authors":["**Simon Gravelle**","David Beyer","Mariano Brito","Alexander Schlaich","Christian Holm"],"categories":null,"content":"","date":1686873600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1686873600,"objectID":"02a104438e830edb04b38e7b907bf1d1","permalink":"https://simongravelle.github.io/publication/2023-reconsruction-of-nmr.html","publishdate":"2023-06-16T00:00:00Z","relpermalink":"/publication/2023-reconsruction-of-nmr.html","section":"publication","summary":"NMR relaxometry is a powerful and well-established experimental approach to characterize dynamic processes in soft matter systems. All-atom (AA) resolved simulations are typically employed to gain further microscopic insights while reproducing the relaxation rates R1. However, such approaches are limited to time and length-scales that hinder modeling of systems like long polymer chains or hydrogels. Coarse-graining (CG) can overcome this barrier at the cost of loosing atomistic details that impede the calculation of NMR relaxation rates. Here, we address this issue by systematic characterization of dipolar relaxation rates R1 while performing systematic measurements on a PEG-H2O mixture at two different levels of details: AA and CG. Remarkably, we show that NMR relaxation rates R1 obtained at the CG level obey the same trends when compared to AA calculations, but with a systematic offset. This offset is due to, on the one hand, the lack of an intra-monomer component and, on the other hand, the inexact positioning of the spin carriers. We show that the offset can be corrected for quantitatively by reconstructing a posteriori the atomistic details for the CG trajectories.","tags":null,"title":"Assessing the validity of NMR relaxation rates obtained from coarse-grained simulations of PEG-water mixtures","type":"publication"},{"authors":["Ángel Díaz Carral","Xiang Xu","**Simon Gravelle**","Azade Yazdan Yar","Siegfried Schmauder","Maria Fyta"],"categories":null,"content":"","date":1686700800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1686700800,"objectID":"f7c6b3c3701b473915b1a423752df30a","permalink":"https://simongravelle.github.io/publication/2023-stability-of-binary.html","publishdate":"2023-06-14T00:00:00Z","relpermalink":"/publication/2023-stability-of-binary.html","section":"publication","summary":"Binary complexes that can be found in copper alloys are investigated in this work through a combination of computer simulations and machine learning. Copper alloys are made of a copper matrix and a combination of single alloying elements in n-ary forms. Due to the coexistence of different types of phases in this matrix, complex regions exist for which information on their precise atomistic structure is missing. In order to uncover such information, we apply active learning and generate moment tensor potentials. This development is based on quantum-mechanical calculations. This approach allows the on-the-fly relaxation of many thousands of potentially novel candidates and check their stability. The ground-state energy of these structures is used to build active learning-generated convex hulls, which are in turn being compared to those from the simulations and the AFLOW database. This procedure provides an insight to additional new stable copper alloy relevant binary complexes. Here, in view of Cu-Ni-Si-Cr alloys, the binary complexes Cu-Si, Ni-Si, Cr-Si, Cr-Ni, Cu-Ni, and Cu-Cr have been investigated. Their stability and the identification of novel stable candidates are discussed based on energetic arguments and the analysis of the respective phonon dispersion. The pipeline followed in this work is able to successfully predict binary phases in Cu-Ni-Si-Cr alloys, specifically for the Cu-Si, Ni-Si, Cr-Ni and Cu-Ni complexes, and to extend the already reported structures in the AFLOW library. In the end, we show the applicability of a predicted Cu-Si stable phase and the developed machine learned potentials at the larger scale of atomistic simulations for the calculation of their mechanical properties and melting behavior. This work provides a computationally efficient framework for material structure prediction and calculation of their properties at a quantum-mechanical accuracy. ","tags":null,"title":"Stability of Binary Precipitates in Cu-Ni-Si-Cr Alloys Investigated Through Active Learning","type":"publication"},{"authors":["**Simon Gravelle**","Sabina Haber-Pohlmeier","Carlos Mattea","Siegfried Stapf","Christian Holm","Alexander Schlaich"],"categories":null,"content":"","date":1684454400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1684454400,"objectID":"3aa1aa539774e6595513786f6283fd5e","permalink":"https://simongravelle.github.io/publication/2023-nmr-investigation-of-water.html","publishdate":"2023-05-19T00:00:00Z","relpermalink":"/publication/2023-nmr-investigation-of-water.html","section":"publication","summary":"The evaporation of water from a bare soil is often accompanied by the formation of a layer of crystallized salt, a process that must be understood in order to address the issue of soil salinisation. Here, we use nuclear magnetic relaxation dispersion measurements to better understand the dynamic properties of water within two types of salt crusts: sodium chloride (NaCl) and sodium sulfate (Na2SO4 ). Our experimental results display a stronger dispersion of the relaxation time T1 with frequency for the case of Na2SO4 as compared to NaCl salt crusts. To gain insight into these results, we perform molecular dynamics simulations of salt solutions confined within slit nanopores made of either NaCl or Na2SO4 . We find a strong dependence of the value of the relaxation time T1 on pore size and salt concentration. Our simulations reveal the complex interplay between the adsorption of ions at the solid surface, the structure of water near the interface, and the dispersion of T1 at low frequency, which we attribute to adsorption-desorption events.","tags":null,"title":"NMR Investigation of Water in Salt Crusts: Insights from Experiments and Molecular Simulations","type":"publication"},{"authors":null,"categories":null,"content":"The version 2.0 of LAMMPS tutorial has just been published, and offers:\na new structure with a sphinx template tutorials are now written in rst format, instead of html, which should facilitate future collaborations a gorgeous dark mode (for the tutorials, not yet for the index page) The version 1.0 is still visible here, but is not maintained and some commands are likely to be obsolete.\n","date":1675555200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1675555200,"objectID":"ee15b0519ba5c1c945f26268fe2520de","permalink":"https://simongravelle.github.io/news/2023-lammpstutorial-v2.0.html","publishdate":"2023-02-05T00:00:00Z","relpermalink":"/news/2023-lammpstutorial-v2.0.html","section":"news","summary":"Now with a new structure and a dark mode!","tags":["Outreach"],"title":"The version 2.0 of LAMMPS tutorials has been released","type":"news"},{"authors":null,"categories":null,"content":"After 2 great years at the ICP in Stuttgart, I am starting my own MSCA project (NanoSep) at LIPhy (UGA) in Benoit Coasne group.\n","date":1675123200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1675123200,"objectID":"66dd1b146c89edb888469dc3743a0900","permalink":"https://simongravelle.github.io/news/2023-liphy-arrival.html","publishdate":"2023-01-29T00:00:00Z","relpermalink":"/news/2023-liphy-arrival.html","section":"news","summary":"My goal is to evaluate the possibility of separating fluid mixtures using nanopores.","tags":["Personal"],"title":"New MSCA project NanoSep starting at UGA","type":"news"},{"authors":null,"categories":null,"content":"The version 0.7 of MAICoS has been released. It comes with:\nan improved documentation with theory and tutorials a ‘Jitter’ option to produce smooth density profiles new modules for cylindrical and spherical geometries ","date":1673481600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1673481600,"objectID":"1f0b2eb6107beabf8ea804767a210803","permalink":"https://simongravelle.github.io/news/2023-maicos-v0.7.html","publishdate":"2023-01-12T00:00:00Z","relpermalink":"/news/2023-maicos-v0.7.html","section":"news","summary":"Use it to analyze your molecular simulations of confined fluids.","tags":["Outreach"],"title":"The version 0.7 of MAICoS has been released","type":"news"},{"authors":["**Simon Gravelle**","Christian Holm","Alexander Schlaich"],"categories":null,"content":"","date":1652832e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1652832e3,"objectID":"0ecde76220f0f90c68bb050ebbd36251","permalink":"https://simongravelle.github.io/publication/2022-transport-of-thin.html","publishdate":"2022-05-18T00:00:00Z","relpermalink":"/publication/2022-transport-of-thin.html","section":"publication","summary":"Under ambient atmospheric conditions, a thin film of water wets many solid surfaces, including insulators, ice, and salt. The film thickness as well as its transport behavior sensitively depend on the surrounding humidity. Understanding this intricate interplay is of the highest relevance for water transport through porous media, particularly in the context of soil salinization induced by evaporation. Here, we use molecular simulations to evaluate the transport properties of thin water films on prototypical salt and soil interfaces, namely NaCl and silica solid surfaces. Our results show two distinct regimes for water transport: at low water coverage, the film permeance scales linearly with the adsorbed amount, in agreement with the activated random walk model. For thicker water films, the permeance scales as the adsorbed amount to the power of 3, in line with the Stokes equation. By comparing results obtained for silica and NaCl surfaces, we find that, at low water coverage, water permeance at the silica surface is considerably lower than at the NaCl surface, which we attribute to difference in hydrogen bonding. We also investigate the effect of atomic surface defects on the transport properties. Finally, in the context of water transport through the porous material, we determine the humidity-dependent crossover between a vapor-dominated and a thin film-dominated transport regimes depending on the pore size.","tags":null,"title":"Transport of thin water films: from thermally activated random walks to hydrodynamics","type":"publication"},{"authors":["Adyant Agrawal","**Simon Gravelle**","Catherine Kamal","Lorenzo Botto"],"categories":null,"content":"","date":1651708800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1651708800,"objectID":"d0401451a881c79dfebceae8fe530191","permalink":"https://simongravelle.github.io/publication/2022-viscous-peeling.html","publishdate":"2022-05-05T00:00:00Z","relpermalink":"/publication/2022-viscous-peeling.html","section":"publication","summary":"Combining molecular dynamics (MD) and continuum simulations, we study the dynamics of propagation of a peeling front in a system composed of multilayered graphene nanosheets completely immersed in water. Peeling is induced by lifting one of the nanosheet edges with an assigned pulling velocity normal to the flat substrate. Using MD, we compute the pulling force as a function of the pulling velocity, and quantify the viscous resistance to the advancement of the peeling front. We compare the MD results to a 1D continuum model of a sheet loaded with modelled hydrodynamic loads. Our results show that the viscous dependence of the force on the velocity is negligible below a threshold velocity. Above this threshold, the hydrodynamics is mainly controlled by the viscous resistance associated to the flow near the crack opening, while lubrication forces are negligible owing to the large hydrodynamic slip at the liquid-solid boundary. Two dissipative mechanisms are identified: a drag resistance to the upward motion of the edge, and a resistance to the gap opening associated to the curvature of the flow streamlines near the entrance. Surprisingly, the shape of the sheet was found to be approximately independent of the pulling velocity even for the largest velocities considered.","tags":null,"title":"Viscous peeling of a nanosheet","type":"publication"},{"authors":["**Simon Gravelle**","Lorenzo Botto"],"categories":null,"content":"","date":1635724800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1635724800,"objectID":"8f6b6171f008721eb519c38848d281cd","permalink":"https://simongravelle.github.io/publication/2021-adsorption-of-single.html","publishdate":"2021-11-01T00:00:00Z","relpermalink":"/publication/2021-adsorption-of-single.html","section":"publication","summary":"The adsorption of graphene-oxide (GO) nanoparticles at the interface between water and vapor was analyzed using all-atom molecular simulations for single and multiple particles. For a single GO particle, our results indicate that the adsorption energy does not scale linearly with the surface coverage of oxygen groups, unlike typically assumed for Janus colloids. Our results also show that the surface activity of the particle depends on the number of surface oxygen groups as well as on their distribution: for a given number of oxygen groups, a GO particle with a patched surface was found to be more surface active than a particle with evenly distributed groups. Then, to understand what sets the thickness of GO layers at interfaces, the adsorption energy of a test GO particle was measured in the presence of multiple GO particles already adsorbed at the interface. Our results indicate that in the case of high degree of oxidation, particle–particle interactions at the water–vapor interface hinder the adsorption of the test particle. In the case of a low degree of oxidation, however, clustering and stacking of GO particles dominate the adsorption behavior, and particle–particle interactions favor the adsorption of the test particle. These results highlight the complexity of multiple particle adsorption and the limitations of single-particle adsorption models when applied to GO at a relatively high surface concentration.","tags":null,"title":"Adsorption of single and multiple graphene oxide nanoparticles at a water-vapor interface","type":"publication"},{"authors":["Catherine Kamal","**Simon Gravelle**","Lorenzo Botto"],"categories":null,"content":"","date":1629244800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1629244800,"objectID":"08ad887cbc4b067991ed06461b62e7d9","permalink":"https://simongravelle.github.io/publication/2021-alignement-of-a-flexible.html","publishdate":"2021-08-18T00:00:00Z","relpermalink":"/publication/2021-alignement-of-a-flexible.html","section":"publication","summary":"Rigid platelike particles displaying interfacial slip can attain a constant orientation in a shear flow when the slip length is sufficiently large. But actual thin particles such as single-layer graphene are flexible and prone to bending deformations when exposed to shear stress. To study the effect of bending deformation on the dynamics of flexible platelike particles with large interfacial slip in a shear flow, we develop a two-dimensional (2D) fluid-structure interaction model. Our model is based on coupling the Euler-Bernoulli beam equation with a boundary integral method to solve the hydrodynamic stress at the particle surface. Emphasis is placed on resolving accurately the stress distribution at the edges of the particle. We find that (i) a stable alignment occurs even for relatively flexible particles and that (ii) edges effects on the shape of the plate are important for values of the length-to-thickness aspect ratio as large as 100. Our results are particularly relevant in view of recent research on the hydrodynamics of suspended flexible sheets made of 2D nanomaterials.","tags":null,"title":"Alignment of a Flexible Plate-like Particle in Shear Flow: Effect of Surface Slip and Edges","type":"publication"},{"authors":["Catherine Kamal","**Simon Gravelle**","Lorenzo Botto"],"categories":null,"content":"","date":1621468800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1621468800,"objectID":"982d52d0e1ba1f8f82aca617d5fcd32e","permalink":"https://simongravelle.github.io/publication/2021-effect-of-hydrodynamic.html","publishdate":"2021-05-20T00:00:00Z","relpermalink":"/publication/2021-effect-of-hydrodynamic.html","section":"publication","summary":"The classical theory by Jeffery predicts that, in the absence of Brownian fluctuations, a thin rigid platelet rotates continuously in a shear flow, performing periodic orbits. However, a stable orientation is possible if the surface of the platelet displays a hydrodynamic slip length λ comparable to or larger than the thickness of the platelet. In this article, by solving the Fokker–Plank equation for the orientation distribution function and corroborating the analysis with boundary integral simulations, we quantify a threshold Péclet number, Pec, above which such alignment occurs. We found that for Pe smaller than Pec, but larger than a second threshold, a regime emerges where Brownian fluctuations are strong enough to break the platelet's alignment and induce rotations, but with a period of rotation that depends on the value of λ. For Pe below this second threshold, slip has a negligible effect on the orientational dynamics. We use these thresholds to classify the dynamics of graphene-like nanoplatelets for realistic values of λ and apply our results to the quantification of the orientational contribution to the effective viscosity of a dilute suspension of nanoplatelets with slip. We find a non-monotonic variation of this term, with a minimum occurring when the slip length is comparable to the thickness of the particle.","tags":null,"title":"Effect of hydrodynamic slip on the rotational dynamics of a thin Brownian platelet in shear flow","type":"publication"},{"authors":["**Simon Gravelle**","Catherine Kamal","Lorenzo Botto"],"categories":null,"content":"","date":1616716800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1616716800,"objectID":"c9b43379e5a74a23273e30f0fd14b978","permalink":"https://simongravelle.github.io/publication/2021-violations-of-jeffery.html","publishdate":"2021-03-26T00:00:00Z","relpermalink":"/publication/2021-violations-of-jeffery.html","section":"publication","summary":"Using molecular dynamics simulations we investigate the shear-induced rotational dynamics of a Brownian nanographene (hexabenzocoronene) freely suspended in a liquid. We demonstrate that, owing to a finite hydrodynamic slip at the molecular surface, these flat molecules tend to align with a constant orientation angle instead of performing the classical periodic orbits predicted by Jeffery's theory. Results are extracted for different Péclet numbers and compared to the predictions by a theory developed for a rigid axisymmetric particle with orientation confined to the flow-gradient plane. The theory is based on the resolution of a one-dimensional Fokker-Planck equation for the angle φ made by one of the particle's diameters with the flow direction. Remarkably, our results show that the essential features of the three-dimensional orientational statistics of the nanographene are captured by the one-dimensional model, given that the hydrodynamic velocity is closed in terms of the slip length λ. Finally, we explore the situation in which multiple nanographenes are suspended in the liquid, and show that slip results in a reduction in specific viscosity.","tags":null,"title":"Violations of Jeffery's theory in the dynamics of nanographene in shear flow","type":"publication"},{"authors":["Catherine Kamal","**Simon Gravelle**","Lorenzo Botto"],"categories":null,"content":"","date":1584576e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1584576e3,"objectID":"f3f6ddd983096bc3445a23c3fd37d9f0","permalink":"https://simongravelle.github.io/publication/2020-hydrodynamic-slip-can-align.html","publishdate":"2020-03-19T00:00:00Z","relpermalink":"/publication/2020-hydrodynamic-slip-can-align.html","section":"publication","summary":"The large-scale processing of nanomaterials such as graphene and MoS2 relies on understanding the flow behaviour of nanometrically-thin platelets suspended in liquids. Here we show, by combining non-equilibrium molecular dynamics and continuum simulations, that rigid nanoplatelets can attain a stable orientation for sufficiently strong flows. Such a stable orientation is in contradiction with the rotational motion predicted by classical colloidal hydrodynamics. This surprising effect is due to hydrodynamic slip at the liquid-solid interface and occurs when the slip length is larger than the platelet thickness; a slip length of a few nanometers may be sufficient to observe alignment. The predictions we developed by examining pure and surface-modified graphene is applicable to different solvent/2D material combinations. The emergence of a fixed orientation in a direction nearly parallel to the flow implies a slip-dependent change in several macroscopic transport properties, with potential impact on applications ranging from functional inks to nanocomposites.","tags":null,"title":"Hydrodynamic slip can align thin nanoplatelets in shear flow","type":"publication"},{"authors":["**Simon Gravelle**","Catherine Kamal","Lorenzo Botto"],"categories":null,"content":"","date":1583712e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1583712e3,"objectID":"b50bc032d4d61cb2ce09c926836ba105","permalink":"https://simongravelle.github.io/publication/2020-liquid-exfoliation.html","publishdate":"2020-03-09T00:00:00Z","relpermalink":"/publication/2020-liquid-exfoliation.html","section":"publication","summary":"Liquid-phase exfoliation, the use of a sheared liquid to delaminate graphite into few-layer graphene, is a promising technique for the large-scale production of graphene. However, the microscale and nanoscale fluid-structure processes controlling the exfoliation are not fully understood. Here, we perform non-equilibrium molecular dynamics simulations of a defect-free graphite nanoplatelet suspended in a shear flow and measure the critical shear rate γ̇ c needed for the exfoliation to occur. We compare γ̇ c for different solvents, including water and N-methyl-pyrrolidone, and nanoplatelets of different lengths. Using a theoretical model based on a balance between the work done by viscous shearing forces and the change in interfacial energies upon layer sliding, we are able to predict the critical shear rates γ̇ c measured in simulations. We find that an accurate prediction of the exfoliation of short graphite nanoplatelets is possible only if both hydrodynamic slip and the fluid forces on the graphene edges are considered and if an accurate value of the solid–liquid surface energy is used. The commonly used “geometric-mean” approximation for the solid–liquid energy leads to grossly incorrect predictions.","tags":null,"title":"Liquid exfoliation of multilayer graphene in sheared solvents: A molecular dynamics investigation","type":"publication"},{"authors":["Pascal Raux","**Simon Gravelle**","Jacques Dumais"],"categories":null,"content":"","date":1579478400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1579478400,"objectID":"06a6b0593fbff727788d83e679c6d1f4","permalink":"https://simongravelle.github.io/publication/2020-design-of-a-unidirectional.html","publishdate":"2020-01-20T00:00:00Z","relpermalink":"/publication/2020-design-of-a-unidirectional.html","section":"publication","summary":"The bromeliad Tillandsia landbeckii thrives in the Atacama desert of Chile using the fog captured by specialized leaf trichomes to satisfy its water needs. However, it is still unclear how the trichome of T. landbeckii and other Tillandsia species is able to absorb fine water droplets during intermittent fog events while also preventing evaporation when the plant is exposed to the desert’s hyperarid conditions. Here, we explain how a 5800-fold asymmetry in water conductance arises from a clever juxtaposition of a thick hygroscopic wall and a semipermeable membrane. While absorption is achieved by osmosis of liquid water, evaporation under dry external conditions shifts the liquid-gas interface forcing water to diffuse through the thick trichome wall in the vapor phase. We confirm this mechanism by fabricating artificial composite membranes mimicking the trichome structure. The reliance on intrinsic material properties instead of moving parts makes the trichome a promising basis for the development of microfluidics valves.","tags":null,"title":"Design of a unidirectional water valve in Tillandsia","type":"publication"},{"authors":["**Simon Gravelle**","Jacques Dumais"],"categories":null,"content":"","date":1578009600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1578009600,"objectID":"1dadce7b7ecdb6ddee779b7741a147fa","permalink":"https://simongravelle.github.io/publication/2020-a-multi-scale-model.html","publishdate":"2020-01-03T00:00:00Z","relpermalink":"/publication/2020-a-multi-scale-model.html","section":"publication","summary":"Tillandsia landbeckii is a rootless plant thriving in the hyper-arid Atacama Desert of Chile. These plants use unique cellulose-based microscopic structures called trichomes to collect fresh water from coastal fog. The trichomes rely on a passive mechanism to maintain an asymmetrical transport of water: they allow for the fast absorption of liquid water deposited by sporadic fog events while preventing evaporation during extended drought periods. Inspired by the trichome’s design, we study fluid transport through a micrometric valve. Combining Grand Canonical Monte Carlo with Non-Equilibrium Molecular Dynamics simulations, we first analyze the adsorption and transport of a fluid through a single nanopore at different chemical potentials. We then scale up the atomic results using a lattice approach, and simulate the transport at the micrometric scale. Results obtained for a model Lennard-Jones fluid and TIP4P/2005 water were compared, allowing us to identify the key physical parameters for achieving a passive hydraulic valve. Our results show that the difference in transport properties of water vapor and liquid water within the cellulose layer is the basis for the ability of the Tillandsia trichome to function as a water valve. Finally, we predict a critical pore dimension above which the cellulose layer can form an efficient valve.","tags":null,"title":"A multi-scale model for fluid transport through a bio-inspired passive valve","type":"publication"},{"authors":["**Simon Gravelle**","Christophe Ybert"],"categories":null,"content":"","date":1577404800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1577404800,"objectID":"a21fb854e4f6fa2120e0dcc5ceb8f248","permalink":"https://simongravelle.github.io/publication/2019-flow-induced.html","publishdate":"2019-12-27T00:00:00Z","relpermalink":"/publication/2019-flow-induced.html","section":"publication","summary":"Despite mass flow being arguably the most elementary transport associated with nanofluidics, its measurement still constitutes a significant bottleneck for the development of this promising field. Here, we investigate how a liquid flow perturbs the ubiquitous enrichment—or depletion—of a solute inside a single nanochannel. Using fluorescence correlation spectroscopy to access the local solute concentration, we demonstrate that the initial enrichment—the so-called Donnan equilibrium—is depleted under flow, thus revealing the underlying mass transport. Combining theoretical and numerical calculations beyond the classical 1D treatment of nanochannels, we rationalize quantitatively our observations and demonstrate unprecedented flow rate sensitivity. Because the present mass transport investigations are based on generic effects, we believe that they can develop into a versatile approach for nanofluidics.","tags":null,"title":"Flow-induced shift of the Donnan equilibrium for ultra-sensitive mass transport measurement through a single nanochannel","type":"publication"},{"authors":["**Simon Gravelle**","Roland R. Netz","Lydéric Bocquet"],"categories":null,"content":"","date":1567123200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1567123200,"objectID":"5b6c563e7db3679adbfc53451aaae974","permalink":"https://simongravelle.github.io/publication/2019-adsorption-kinetics.html","publishdate":"2019-08-30T00:00:00Z","relpermalink":"/publication/2019-adsorption-kinetics.html","section":"publication","summary":"Ionic current measurements through solid-state nanopores consistently show a power spectral density that scales as 1/f α at low frequency f, with an exponent α ∼ 0.5–1.5, but strikingly, the physical origin of this behavior remains elusive. Here, we perform simulations of particles reversibly adsorbing at the surface of a nanopore and show that the fluctuations in the number of adsorbed particles exhibit low-frequency pink noise. We furthermore propose theoretical modeling for the time-dependent adsorption of particles on the nanopore surface for various geometries, which predicts a frequency spectrum in very good agreement with the simulation results. Altogether, our results highlight that the low-frequency noise takes its origin in the reversible adsorption of ions at the pore surface combined with the long-lasting excursions of the ions in the reservoirs. The scaling regime of the power spectrum extends down to a cutoff frequency which is far smaller than simple diffusion estimates. Using realistic values for the pore dimensions and the adsorption–desorption kinetics, this predicts the observation of pink noise for frequencies down to the hertz for a typical solid-state nanopore, in good agreement with experiments.","tags":null,"title":"Adsorption Kinetics in Open Nanopores as a Source of Low-Frequency Noise","type":"publication"},{"authors":["Lyderic Bocquet","Alessandro Siria","Benoit Laborie","Hiroaki Yoshida","Simon Gravelle"],"categories":null,"content":"","date":1490572800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1490572800,"objectID":"69861247e11c1c15342b4db861d37d43","permalink":"https://simongravelle.github.io/publication/2016-use-of-nanoporous.html","publishdate":"2017-03-27T00:00:00Z","relpermalink":"/publication/2016-use-of-nanoporous.html","section":"publication","summary":"The invention relates to the extraction of organic compounds from mixtures of said compounds with water, using a nanoporous carbon membrane. The invention can be used in any field where it is desired to separate an organic compound of interest from water, such as the drying of alcohols or alkanes.","tags":null,"title":"Use of nanoporous carbon membranes for separating aqueous/organic mixtures","type":"publication"},{"authors":["**Simon Gravelle**","Hiroaki Yoshida","Laurent Joly","Christophe Ybert","Lydéric Bocquet"],"categories":null,"content":"","date":1474934400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1474934400,"objectID":"85e25b5671220294508f558d2cb86e70","permalink":"https://simongravelle.github.io/publication/2016-carbon-membrane.html","publishdate":"2016-09-27T00:00:00Z","relpermalink":"/publication/2016-carbon-membrane.html","section":"publication","summary":"We demonstrate, on the basis of molecular dynamics simulations, the possibility of an efficient water-ethanol separation using nanoporous carbon membranes, namely, carbon nanotube membranes, nanoporous graphene sheets, and multilayer graphene membranes. While these carbon membranes are in general permeable to both pure liquids, they exhibit a counter-intuitive “self-semi-permeability” to water in the presence of water-ethanol mixtures. This originates in a preferred ethanol adsorption in nanoconfinement that prevents water molecules from entering the carbon nanopores. An osmotic pressure is accordingly expressed across the carbon membranes for the water-ethanol mixture, which agrees with the classic van’t Hoff type expression. This suggests a robust and versatile membrane-based separation, built on a pressure-driven reverse-osmosis process across these carbon-based membranes. In particular, the recent development of large-scale “graphene-oxide” like membranes then opens an avenue for a versatile and efficient ethanol dehydration using this separation process, with possible application for bio-ethanol fabrication.","tags":null,"title":"Carbon membranes for efficient water-ethanol separation","type":"publication"},{"authors":["Adrien Guérin","**Simon Gravelle**","Lydéric Bocquet"],"categories":null,"content":"","date":1468972800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1468972800,"objectID":"7633fb7583f59073d092204e0fea3327","permalink":"https://simongravelle.github.io/publication/2016-forces-behind.html","publishdate":"2016-07-20T00:00:00Z","relpermalink":"/publication/2016-forces-behind.html","section":"publication","summary":"The cell theory developed in the early 19th century teaches us that only cells beget cells (1). As a consequence, the evolution of life on Earth is but a long sequence of cell divisions; wherever this sequence is broken, life ends. Cell division is not only how organisms perpetuate themselves, it is also one way in which complexity is built during development. The contribution of cell division to development is particularly striking in plants because plant cells are surrounded by stiff walls, making them clearly distinguishable from each other and fixing their spatial relation by preventing cell migration (...)","tags":null,"title":"Forces behind plant cell division","type":"publication"},{"authors":["**Simon Gravelle**","Christophe Ybert","Lydéric Bocquet","Laurent Joly"],"categories":null,"content":"","date":1458777600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1458777600,"objectID":"3b047b9bda6e6c46ff94f2c17e7eb74b","permalink":"https://simongravelle.github.io/publication/2016-anomalous-capillary.html","publishdate":"2016-03-24T00:00:00Z","relpermalink":"/publication/2016-anomalous-capillary.html","section":"publication","summary":"This work revisits capillary filling dynamics in the regime of nanometric to subnanometric channels. Using molecular dynamics simulations of water in carbon nanotubes, we show that for tube radii below one nanometer, both the filling velocity and the Jurin rise vary nonmonotonically with the tube radius. Strikingly, with fixed chemical surface properties, this leads to confinement-induced reversal of the tube wettability from hydrophilic to hydrophobic for specific values of the radius. By comparing with a model liquid metal, we show that these effects are not specific to water. Using complementary data from slit channels, we then show that they can be described using the disjoining pressure associated with the liquid structuring in confinement. This breakdown of the standard continuum framework is of main importance in the context of capillary effects in nanoporous media, with potential interests ranging from membrane selectivity to mechanical energy storage.","tags":null,"title":"Anomalous capillary filling and wettability reversal in nanochannels","type":"publication"},{"authors":["**Simon Gravelle**"],"categories":null,"content":"","date":1456790400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1456790400,"objectID":"95db3f45aa3ce1e77f82a5daef778878","permalink":"https://simongravelle.github.io/publication/2015-nanofluidics-a-pedagogical.html","publishdate":"2016-03-01T00:00:00Z","relpermalink":"/publication/2015-nanofluidics-a-pedagogical.html","section":"publication","summary":"Nanofluidics is the study of fluids confined in structures of nanometric dimensions (typically 1 − 100 nm). Fluids confined in these structures exhibit behaviours that are not observed in larger structures, due to a high surface to bulk ratio (...)","tags":null,"title":" Nanofluidics: a pedagogical introduction ","type":"publication"},{"authors":["**Simon Gravelle**"],"categories":null,"content":"","date":1447718400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1447718400,"objectID":"d48b275814aabf96eed8441d234f416c","permalink":"https://simongravelle.github.io/publication/2015-nanofluidics-a-theoretical.html","publishdate":"2015-11-17T00:00:00Z","relpermalink":"/publication/2015-nanofluidics-a-theoretical.html","section":"publication","summary":"Nanofluidics is the study of fluids confined in structures of nanometric dimensions (typically 1 − 100 nm). Fluids confined in these structures exhibit behaviours that are not observed in larger structures, due to a high surface to bulk ratio (...)","tags":null,"title":"Nanofluidics: a theoretical and numerical investigation of fluid transport in nanochannels","type":"publication"},{"authors":["**Simon Gravelle**","Laurent Joly","François Detcheverry","Christophe Ybert","Cécile Cottin-Bizonne","Lydéric Bocquet"],"categories":null,"content":"","date":1425427200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1425427200,"objectID":"41d6459fc279c1e47b30edf7bff5f2f0","permalink":"https://simongravelle.github.io/publication/2015-permeabilite-optimale.html","publishdate":"2015-03-04T00:00:00Z","relpermalink":"/publication/2015-permeabilite-optimale.html","section":"publication","summary":"Les aquaporines sont des protéines transmembranaires omniprésentes dans le corps humain. Insérées dans les membranes cellulaires, elles jouent un rôle important dans la filtration, l’absorption et la sécrétion des fluides. L’excellent compromis entre sélectivité et perméabilité à l’eau des aquaporines reste mal compris aujourd’hui. Dans ce travail, nous nous intéressons à la forme en sablier des aquaporines, dont nous étudions l’influence sur la perméabilité, à l’aide de calculs numériques et d’un modèle théorique simple. Nous montrons qu’il existe un angle d’ouverture optimal qui maximise la perméabilité, et dont la valeur est proche des angles observés dans les aquaporines.","tags":null,"title":"Perméabilité optimale des aquaporines : une histoire de forme?","type":"publication"},{"authors":["**Simon Gravelle**","Laurent Joly","Christophe Ybert","Lydéric Bocquet"],"categories":null,"content":"","date":1412812800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1412812800,"objectID":"332b41c66c17a5ecadd631be711e12ea","permalink":"https://simongravelle.github.io/publication/2014-large-permeabilities.html","publishdate":"2014-10-09T00:00:00Z","relpermalink":"/publication/2014-large-permeabilities.html","section":"publication","summary":"In fluid transport across nanopores, there is a fundamental dissipation that arises from the connection between the pore and the macroscopic reservoirs. This entrance effect can hinder the whole transport in certain situations, for short pores and/or highly slipping channels. In this paper, we explore the hydrodynamic permeability of hourglass shape nanopores using molecular dynamics (MD) simulations, with the central pore size ranging from several nanometers down to a few Angströms. Surprisingly, we find a very good agreement between MD results and continuum hydrodynamic predictions, even for the smallest systems undergoing single file transport of water. An optimum of permeability is found for an opening angle around 5°, in agreement with continuum predictions, yielding a permeability five times larger than for a straight nanotube. Moreover, we find that the permeability of hourglass shape nanopores is even larger than single nanopores pierced in a molecular thin graphene sheet. This suggests that designing the geometry of nanopores may help considerably increasing the macroscopic permeability of membranes.","tags":null,"title":"Large permeabilities of hourglass nanopores: From hydrodynamics to single file transport","type":"publication"},{"authors":["Alessandro Gadaleta","Catherine Sempere","**Simon Gravelle**","Alessandro Siria","Rémy Fulcrand","Christophe Ybert","Lydéric Bocquet"],"categories":null,"content":"","date":1391126400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1391126400,"objectID":"49777b08f28d3a441a4d069a4b46dfe8","permalink":"https://simongravelle.github.io/publication/2014-sub-additive.html","publishdate":"2014-01-31T00:00:00Z","relpermalink":"/publication/2014-sub-additive.html","section":"publication","summary":"Nanopores, either biological, solid-state, or ultrathin pierced graphene, are powerful tools which are central to many applications, from sensing of biological molecules to desalination and fabrication of ion selective membranes. However, the interpretation of transport through low aspect-ratio nanopores becomes particularly complex as 3D access effects outside the pores are expected to play a dominant role. Here, we report both experiments and theory showing that, in contrast to naïve expectations, long-range mutual interaction across an array of nanopores leads to a non-extensive, sub-linear scaling of the global conductance on the number of pores N. A scaling analysis demonstrates that the N-dependence of the conductance depends on the topology of the network. It scales like G ∼ N/log N for a 1D line of pores, and like G∼N−−√ for a 2D array, in agreement with experimental measurements. Our results can be extended to alternative transport phenomena obeying Laplace equations, such as diffusive, thermal, or hydrodynamic transport. Consequences of this counter-intuitive behavior are discussed in the context of transport across thin membranes, with applications in energy harvesting.","tags":null,"title":"Sub-additive ionic transport across arrays of solid-state nanopores","type":"publication"},{"authors":["Clara Picallo","**Simon Gravelle**","Laurent Joly","Elisabeth Charlaix","Lydéric Bocquet"],"categories":null,"content":"","date":138672e4,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":138672e4,"objectID":"39b299f33f1e3af97aeef633de84ff41","permalink":"https://simongravelle.github.io/publication/2013-nanofluidic-osmotic.html","publishdate":"2013-12-11T00:00:00Z","relpermalink":"/publication/2013-nanofluidic-osmotic.html","section":"publication","summary":"Osmosis describes the flow of water across semipermeable membranes powered by the chemical free energy extracted from salinity gradients. While osmosis can be expressed in simple terms via the van ’t Hoff ideal gas formula for the osmotic pressure, it is a complex phenomenon taking its roots in the subtle interactions occurring at the scale of the membrane nanopores. Here we use new opportunities offered by nanofluidic systems to create an osmotic diode exhibiting asymmetric water flow under reversal of osmotic driving. We show that a surface charge asymmetry built on a nanochannel surface leads to nonlinear couplings between water flow and the ion dynamics, which are capable of water flow rectification. This phenomenon opens new opportunities for water purification and complex flow control in nanochannels.","tags":null,"title":"Nanofluidic osmotic diodes: Theory and molecular dynamics simulations","type":"publication"},{"authors":["**Simon Gravelle**","Laurent Joly","François Detcheverry","Christophe Ybert","Cécile Cottin-Bizonne","Lydéric Bocquet"],"categories":null,"content":"","date":1380067200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1380067200,"objectID":"966c17ea8b9020cf61760b49d2106003","permalink":"https://simongravelle.github.io/publication/2012-optimizing-water.html","publishdate":"2013-09-25T00:00:00Z","relpermalink":"/publication/2012-optimizing-water.html","section":"publication","summary":"Aquaporin channels are able to selectively conduct water across cell membranes, with remarkable efficiency. Although molecular details are crucial to the pore performance, permeability is also strongly limited by viscous dissipation at the entrances. Could the hourglass shape of aquaporins optimize such entrance effects? We show that conical entrances with suitable opening angle can indeed provide a large increase of the channel permeability. Strikingly, the optimal opening angles compare well with the angles measured in a large variety of aquaporins, suggesting that their hourglass shape could be the result of a natural selection process toward optimal permeability. This work also provides guidelines to optimize the performances of artificial nanopores, with applications in desalination, ultrafiltration, or energy conversion.","tags":null,"title":"Optimizing water permeability through the hourglass shape of aquaporins","type":"publication"}]
\ No newline at end of file
+[{"authors":null,"categories":null,"content":"About me\nI am a CNRS researcher at LIPhy in Grenoble, France. I use molecular simulations to study fluids at interfaces and soft matter systems.\nOpen source and open data\nI share all the codes developed as part of my research as open source, see for instance:\nmy Github repository containing molecular simulation scripts and data, NMRforMD, a Python script for calculating hydrogen NMR relaxation rates from molecular dynamics simulations, In parallel to my open-source projects, I have been involved in the development of MAICoS, a Python toolkit for analyzing confined molecular simulations.\nOutreach\nIn parallel to my research activities, I am developing several outreach projects, including:\nthe LAMMPS tutorials webpage and its associated repositories, MDCourse: Learn Molecular Simulations with Python, the GROMACS tutorials page, a gallery of animations and molecular art. ","date":-62135596800,"expirydate":-62135596800,"kind":"term","lang":"en","lastmod":-62135596800,"objectID":"2525497d367e79493fd32b198b28f040","permalink":"","publishdate":"0001-01-01T00:00:00Z","relpermalink":"","section":"authors","summary":"About me\nI am a CNRS researcher at LIPhy in Grenoble, France. I use molecular simulations to study fluids at interfaces and soft matter systems.\nOpen source and open data","tags":null,"title":"Simon Gravelle","type":"authors"},{"authors":[],"categories":null,"content":" Click on the Slides button above to view the built-in slides feature. Slides can be added in a few ways:\nCreate slides using Wowchemy’s Slides feature and link using slides parameter in the front matter of the talk file Upload an existing slide deck to static/ and link using url_slides parameter in the front matter of the talk file Embed your slides (e.g. Google Slides) or presentation video on this page using shortcodes. Further event details, including page elements such as image galleries, can be added to the body of this page.\n","date":1906549200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1906549200,"objectID":"a8edef490afe42206247b6ac05657af0","permalink":"https://simongravelle.github.io/talk/example-talk.html","publishdate":"2017-01-01T00:00:00Z","relpermalink":"/talk/example-talk.html","section":"event","summary":"An example talk using Wowchemy's Markdown slides feature.","tags":[],"title":"Example Talk","type":"event"},{"authors":null,"categories":null,"content":"","date":1697328e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1697328e3,"objectID":"01b5f0738efb9f4ac8fc3559d8fd6ca8","permalink":"https://simongravelle.github.io/gallery/graphene.html","publishdate":"2023-10-15T00:00:00Z","relpermalink":"/gallery/graphene.html","section":"gallery","summary":"","tags":null,"title":"Wave in graphene","type":"gallery"},{"authors":null,"categories":null,"content":"","date":1696896e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1696896e3,"objectID":"e9441bf62787bdcbbf4f79a8c7ec421a","permalink":"https://simongravelle.github.io/gallery/fullrene.html","publishdate":"2023-10-10T00:00:00Z","relpermalink":"/gallery/fullrene.html","section":"gallery","summary":"","tags":null,"title":"Fullerene collision","type":"gallery"},{"authors":null,"categories":null,"content":"","date":1696464e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1696464e3,"objectID":"a4afb40bb80bd0d47a437bd23e31f11e","permalink":"https://simongravelle.github.io/gallery/ring.html","publishdate":"2023-10-05T00:00:00Z","relpermalink":"/gallery/ring.html","section":"gallery","summary":"","tags":null,"title":"The molecular ring","type":"gallery"},{"authors":null,"categories":null,"content":"Update. The offer has now expired, and the selection process has moved to the next step.\nScope. With the goal to reach carbon neutrality by 2050, direct air capture (DAC) of CO2 from wet flue gases is one brick of the carbon mitigation strategy – especially with the next generation of solid porous sorbents based on Metal-Organic Frameworks (MOF). While thermodynamics of the CO2 capture is well documented in the literature, little is known about molecular diffusion and transport properties in MOF angstropores (in particular, in the presence of environmental humidity). Also, diffusion through pore scales of the applicative sorbing medium, ranging from nanopores (pore diameter ~nm) to macropores (\u0026gt; 50 nm) and beyond remain open. In order to fill the gap and gain insight into multiscale transport properties and try to figure CO2 capture optimization through MOF based sorbents, we ambition to develop a multiscale approach based on a lattice model fed by molecular simulations.\nIn more detail, the objective of this PhD proposal is two-fold. i. Using molecular simulations [e.g. Magnin et al. J. Phys. Chem. C 2022], we aim to unravel the molecular phenomena that govern the thermodynamic and kinetic mechanisms when capturing CO2 using a multi-scale porous material. With this first aspect, we aim to rationalize the use of nanoporous materials for practical engineering processes by developing a robust and general methodology to link physico-chemical properties at different scales. ii. Using a bottom-up strategy, we will upscale the results obtained using atomistic simulations to mimic phase separation and transport of CO2/N2/H2O mixtures at the macroscale. To do so, a simple yet realistic lattice model [Botan et al. Phys. Rev. E 2015], which can be seen as a pore network model accounting for the change of the local thermodynamic/transport properties in a kinetic engineering process (e.g. Pressure Swing Adsorption), will be used.\nPotential candidate. The PhD candidate should have a background in physics, physical chemistry/chemical physics or materials science. He/she should also have some experience in scientific programming and a background in statistical mechanics (including if possible Monte Carlo or/and Molecular Dynamics).\nPractical aspects. The position is available starting January 2024 and lasts for 36 months. The PhD student will work under the supervision of Benoit Coasne/Simon Gravelle (LIPhy, Grenoble) and Yann Magnin (CSTJF, Pau). He/she will be located at LIPhy in Grenoble, France but several short stays in CSTJF in Pau, France will be planned. Applicants should provide a CV, a letter of motivation and the names and email addresses of 2 or 3 references to:\nYann Magnin (yann.magnin at totalenergies.com) Benoit Coasne (benoit.coasne at univ-grenoble-alpes.fr) Simon Gravelle (simon.gravelle at univ-grenoble-alpes.fr) More information:\nhttps://benoitcoasne.github.io/ (Coasne’s research group website) https://www.yann-magnin.fr/ (research website) ","date":1688947200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1688947200,"objectID":"bcbcff3cc776cd413546f797aaac134f","permalink":"https://simongravelle.github.io/news/2023-phd-offer.html","publishdate":"2023-07-10T00:00:00Z","relpermalink":"/news/2023-phd-offer.html","section":"news","summary":"CO2 Capture Using Nanoporous Adsorbents -- A Multiscale Numerical Approach From Molecular Aspects to the Engineering Scale","tags":["Job"],"title":"PhD Position Available in LIPhy (Filled)","type":"news"},{"authors":null,"categories":null,"content":"In the continuity of my MSCA fellowship, I’ve been hired by the French CNRS (Section 11) as a tenured full time researcher at LIPhy (UGA).\n","date":1687996800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1687996800,"objectID":"d9cfc7a9d756d2a010e13ea6d11dcf56","permalink":"https://simongravelle.github.io/news/2023-cnrs-start.html","publishdate":"2023-06-29T00:00:00Z","relpermalink":"/news/2023-cnrs-start.html","section":"news","summary":"I will be mainly working on the separation of fluid mixture using soft matter membrane, in LiPhy, Grenoble.","tags":["Personal"],"title":"I have obtained a position at French CNRS","type":"news"},{"authors":["**Simon Gravelle**","David Beyer","Mariano Brito","Alexander Schlaich","Christian Holm"],"categories":null,"content":"","date":1686873600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1686873600,"objectID":"02a104438e830edb04b38e7b907bf1d1","permalink":"https://simongravelle.github.io/publication/2023-reconsruction-of-nmr.html","publishdate":"2023-06-16T00:00:00Z","relpermalink":"/publication/2023-reconsruction-of-nmr.html","section":"publication","summary":"NMR relaxometry is a powerful and well-established experimental approach to characterize dynamic processes in soft matter systems. All-atom (AA) resolved simulations are typically employed to gain further microscopic insights while reproducing the relaxation rates R1. However, such approaches are limited to time and length-scales that hinder modeling of systems like long polymer chains or hydrogels. Coarse-graining (CG) can overcome this barrier at the cost of loosing atomistic details that impede the calculation of NMR relaxation rates. Here, we address this issue by systematic characterization of dipolar relaxation rates R1 while performing systematic measurements on a PEG-H2O mixture at two different levels of details: AA and CG. Remarkably, we show that NMR relaxation rates R1 obtained at the CG level obey the same trends when compared to AA calculations, but with a systematic offset. This offset is due to, on the one hand, the lack of an intra-monomer component and, on the other hand, the inexact positioning of the spin carriers. We show that the offset can be corrected for quantitatively by reconstructing a posteriori the atomistic details for the CG trajectories.","tags":null,"title":"Assessing the validity of NMR relaxation rates obtained from coarse-grained simulations of PEG-water mixtures","type":"publication"},{"authors":["Ángel Díaz Carral","Xiang Xu","**Simon Gravelle**","Azade Yazdan Yar","Siegfried Schmauder","Maria Fyta"],"categories":null,"content":"","date":1686700800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1686700800,"objectID":"f7c6b3c3701b473915b1a423752df30a","permalink":"https://simongravelle.github.io/publication/2023-stability-of-binary.html","publishdate":"2023-06-14T00:00:00Z","relpermalink":"/publication/2023-stability-of-binary.html","section":"publication","summary":"Binary complexes that can be found in copper alloys are investigated in this work through a combination of computer simulations and machine learning. Copper alloys are made of a copper matrix and a combination of single alloying elements in n-ary forms. Due to the coexistence of different types of phases in this matrix, complex regions exist for which information on their precise atomistic structure is missing. In order to uncover such information, we apply active learning and generate moment tensor potentials. This development is based on quantum-mechanical calculations. This approach allows the on-the-fly relaxation of many thousands of potentially novel candidates and check their stability. The ground-state energy of these structures is used to build active learning-generated convex hulls, which are in turn being compared to those from the simulations and the AFLOW database. This procedure provides an insight to additional new stable copper alloy relevant binary complexes. Here, in view of Cu-Ni-Si-Cr alloys, the binary complexes Cu-Si, Ni-Si, Cr-Si, Cr-Ni, Cu-Ni, and Cu-Cr have been investigated. Their stability and the identification of novel stable candidates are discussed based on energetic arguments and the analysis of the respective phonon dispersion. The pipeline followed in this work is able to successfully predict binary phases in Cu-Ni-Si-Cr alloys, specifically for the Cu-Si, Ni-Si, Cr-Ni and Cu-Ni complexes, and to extend the already reported structures in the AFLOW library. In the end, we show the applicability of a predicted Cu-Si stable phase and the developed machine learned potentials at the larger scale of atomistic simulations for the calculation of their mechanical properties and melting behavior. This work provides a computationally efficient framework for material structure prediction and calculation of their properties at a quantum-mechanical accuracy. ","tags":null,"title":"Stability of Binary Precipitates in Cu-Ni-Si-Cr Alloys Investigated Through Active Learning","type":"publication"},{"authors":["**Simon Gravelle**","Sabina Haber-Pohlmeier","Carlos Mattea","Siegfried Stapf","Christian Holm","Alexander Schlaich"],"categories":null,"content":"","date":1684454400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1684454400,"objectID":"3aa1aa539774e6595513786f6283fd5e","permalink":"https://simongravelle.github.io/publication/2023-nmr-investigation-of-water.html","publishdate":"2023-05-19T00:00:00Z","relpermalink":"/publication/2023-nmr-investigation-of-water.html","section":"publication","summary":"The evaporation of water from a bare soil is often accompanied by the formation of a layer of crystallized salt, a process that must be understood in order to address the issue of soil salinisation. Here, we use nuclear magnetic relaxation dispersion measurements to better understand the dynamic properties of water within two types of salt crusts: sodium chloride (NaCl) and sodium sulfate (Na2SO4 ). Our experimental results display a stronger dispersion of the relaxation time T1 with frequency for the case of Na2SO4 as compared to NaCl salt crusts. To gain insight into these results, we perform molecular dynamics simulations of salt solutions confined within slit nanopores made of either NaCl or Na2SO4 . We find a strong dependence of the value of the relaxation time T1 on pore size and salt concentration. Our simulations reveal the complex interplay between the adsorption of ions at the solid surface, the structure of water near the interface, and the dispersion of T1 at low frequency, which we attribute to adsorption-desorption events.","tags":null,"title":"NMR Investigation of Water in Salt Crusts: Insights from Experiments and Molecular Simulations","type":"publication"},{"authors":null,"categories":null,"content":"The version 2.0 of LAMMPS tutorial has just been published, and offers:\na new structure with a sphinx template tutorials are now written in rst format, instead of html, which should facilitate future collaborations a gorgeous dark mode (for the tutorials, not yet for the index page) The version 1.0 is still visible here, but is not maintained and some commands are likely to be obsolete.\n","date":1675555200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1675555200,"objectID":"ee15b0519ba5c1c945f26268fe2520de","permalink":"https://simongravelle.github.io/news/2023-lammpstutorial-v2.0.html","publishdate":"2023-02-05T00:00:00Z","relpermalink":"/news/2023-lammpstutorial-v2.0.html","section":"news","summary":"Now with a new structure and a dark mode!","tags":["Outreach"],"title":"The version 2.0 of LAMMPS tutorials has been released","type":"news"},{"authors":null,"categories":null,"content":"After 2 great years at the ICP in Stuttgart, I am starting my own MSCA project (NanoSep) at LIPhy (UGA) in Benoit Coasne group.\n","date":1675123200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1675123200,"objectID":"66dd1b146c89edb888469dc3743a0900","permalink":"https://simongravelle.github.io/news/2023-liphy-arrival.html","publishdate":"2023-01-29T00:00:00Z","relpermalink":"/news/2023-liphy-arrival.html","section":"news","summary":"My goal is to evaluate the possibility of separating fluid mixtures using nanopores.","tags":["Personal"],"title":"New MSCA project NanoSep starting at UGA","type":"news"},{"authors":null,"categories":null,"content":"The version 0.7 of MAICoS has been released. It comes with:\nan improved documentation with theory and tutorials a ‘Jitter’ option to produce smooth density profiles new modules for cylindrical and spherical geometries ","date":1673481600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1673481600,"objectID":"1f0b2eb6107beabf8ea804767a210803","permalink":"https://simongravelle.github.io/news/2023-maicos-v0.7.html","publishdate":"2023-01-12T00:00:00Z","relpermalink":"/news/2023-maicos-v0.7.html","section":"news","summary":"Use it to analyze your molecular simulations of confined fluids.","tags":["Outreach"],"title":"The version 0.7 of MAICoS has been released","type":"news"},{"authors":["**Simon Gravelle**","Christian Holm","Alexander Schlaich"],"categories":null,"content":"","date":1652832e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1652832e3,"objectID":"0ecde76220f0f90c68bb050ebbd36251","permalink":"https://simongravelle.github.io/publication/2022-transport-of-thin.html","publishdate":"2022-05-18T00:00:00Z","relpermalink":"/publication/2022-transport-of-thin.html","section":"publication","summary":"Under ambient atmospheric conditions, a thin film of water wets many solid surfaces, including insulators, ice, and salt. The film thickness as well as its transport behavior sensitively depend on the surrounding humidity. Understanding this intricate interplay is of the highest relevance for water transport through porous media, particularly in the context of soil salinization induced by evaporation. Here, we use molecular simulations to evaluate the transport properties of thin water films on prototypical salt and soil interfaces, namely NaCl and silica solid surfaces. Our results show two distinct regimes for water transport: at low water coverage, the film permeance scales linearly with the adsorbed amount, in agreement with the activated random walk model. For thicker water films, the permeance scales as the adsorbed amount to the power of 3, in line with the Stokes equation. By comparing results obtained for silica and NaCl surfaces, we find that, at low water coverage, water permeance at the silica surface is considerably lower than at the NaCl surface, which we attribute to difference in hydrogen bonding. We also investigate the effect of atomic surface defects on the transport properties. Finally, in the context of water transport through the porous material, we determine the humidity-dependent crossover between a vapor-dominated and a thin film-dominated transport regimes depending on the pore size.","tags":null,"title":"Transport of thin water films: from thermally activated random walks to hydrodynamics","type":"publication"},{"authors":["Adyant Agrawal","**Simon Gravelle**","Catherine Kamal","Lorenzo Botto"],"categories":null,"content":"","date":1651708800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1651708800,"objectID":"d0401451a881c79dfebceae8fe530191","permalink":"https://simongravelle.github.io/publication/2022-viscous-peeling.html","publishdate":"2022-05-05T00:00:00Z","relpermalink":"/publication/2022-viscous-peeling.html","section":"publication","summary":"Combining molecular dynamics (MD) and continuum simulations, we study the dynamics of propagation of a peeling front in a system composed of multilayered graphene nanosheets completely immersed in water. Peeling is induced by lifting one of the nanosheet edges with an assigned pulling velocity normal to the flat substrate. Using MD, we compute the pulling force as a function of the pulling velocity, and quantify the viscous resistance to the advancement of the peeling front. We compare the MD results to a 1D continuum model of a sheet loaded with modelled hydrodynamic loads. Our results show that the viscous dependence of the force on the velocity is negligible below a threshold velocity. Above this threshold, the hydrodynamics is mainly controlled by the viscous resistance associated to the flow near the crack opening, while lubrication forces are negligible owing to the large hydrodynamic slip at the liquid-solid boundary. Two dissipative mechanisms are identified: a drag resistance to the upward motion of the edge, and a resistance to the gap opening associated to the curvature of the flow streamlines near the entrance. Surprisingly, the shape of the sheet was found to be approximately independent of the pulling velocity even for the largest velocities considered.","tags":null,"title":"Viscous peeling of a nanosheet","type":"publication"},{"authors":["**Simon Gravelle**","Lorenzo Botto"],"categories":null,"content":"","date":1635724800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1635724800,"objectID":"8f6b6171f008721eb519c38848d281cd","permalink":"https://simongravelle.github.io/publication/2021-adsorption-of-single.html","publishdate":"2021-11-01T00:00:00Z","relpermalink":"/publication/2021-adsorption-of-single.html","section":"publication","summary":"The adsorption of graphene-oxide (GO) nanoparticles at the interface between water and vapor was analyzed using all-atom molecular simulations for single and multiple particles. For a single GO particle, our results indicate that the adsorption energy does not scale linearly with the surface coverage of oxygen groups, unlike typically assumed for Janus colloids. Our results also show that the surface activity of the particle depends on the number of surface oxygen groups as well as on their distribution: for a given number of oxygen groups, a GO particle with a patched surface was found to be more surface active than a particle with evenly distributed groups. Then, to understand what sets the thickness of GO layers at interfaces, the adsorption energy of a test GO particle was measured in the presence of multiple GO particles already adsorbed at the interface. Our results indicate that in the case of high degree of oxidation, particle–particle interactions at the water–vapor interface hinder the adsorption of the test particle. In the case of a low degree of oxidation, however, clustering and stacking of GO particles dominate the adsorption behavior, and particle–particle interactions favor the adsorption of the test particle. These results highlight the complexity of multiple particle adsorption and the limitations of single-particle adsorption models when applied to GO at a relatively high surface concentration.","tags":null,"title":"Adsorption of single and multiple graphene oxide nanoparticles at a water-vapor interface","type":"publication"},{"authors":["Catherine Kamal","**Simon Gravelle**","Lorenzo Botto"],"categories":null,"content":"","date":1629244800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1629244800,"objectID":"08ad887cbc4b067991ed06461b62e7d9","permalink":"https://simongravelle.github.io/publication/2021-alignement-of-a-flexible.html","publishdate":"2021-08-18T00:00:00Z","relpermalink":"/publication/2021-alignement-of-a-flexible.html","section":"publication","summary":"Rigid platelike particles displaying interfacial slip can attain a constant orientation in a shear flow when the slip length is sufficiently large. But actual thin particles such as single-layer graphene are flexible and prone to bending deformations when exposed to shear stress. To study the effect of bending deformation on the dynamics of flexible platelike particles with large interfacial slip in a shear flow, we develop a two-dimensional (2D) fluid-structure interaction model. Our model is based on coupling the Euler-Bernoulli beam equation with a boundary integral method to solve the hydrodynamic stress at the particle surface. Emphasis is placed on resolving accurately the stress distribution at the edges of the particle. We find that (i) a stable alignment occurs even for relatively flexible particles and that (ii) edges effects on the shape of the plate are important for values of the length-to-thickness aspect ratio as large as 100. Our results are particularly relevant in view of recent research on the hydrodynamics of suspended flexible sheets made of 2D nanomaterials.","tags":null,"title":"Alignment of a Flexible Plate-like Particle in Shear Flow: Effect of Surface Slip and Edges","type":"publication"},{"authors":["Catherine Kamal","**Simon Gravelle**","Lorenzo Botto"],"categories":null,"content":"","date":1621468800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1621468800,"objectID":"982d52d0e1ba1f8f82aca617d5fcd32e","permalink":"https://simongravelle.github.io/publication/2021-effect-of-hydrodynamic.html","publishdate":"2021-05-20T00:00:00Z","relpermalink":"/publication/2021-effect-of-hydrodynamic.html","section":"publication","summary":"The classical theory by Jeffery predicts that, in the absence of Brownian fluctuations, a thin rigid platelet rotates continuously in a shear flow, performing periodic orbits. However, a stable orientation is possible if the surface of the platelet displays a hydrodynamic slip length λ comparable to or larger than the thickness of the platelet. In this article, by solving the Fokker–Plank equation for the orientation distribution function and corroborating the analysis with boundary integral simulations, we quantify a threshold Péclet number, Pec, above which such alignment occurs. We found that for Pe smaller than Pec, but larger than a second threshold, a regime emerges where Brownian fluctuations are strong enough to break the platelet's alignment and induce rotations, but with a period of rotation that depends on the value of λ. For Pe below this second threshold, slip has a negligible effect on the orientational dynamics. We use these thresholds to classify the dynamics of graphene-like nanoplatelets for realistic values of λ and apply our results to the quantification of the orientational contribution to the effective viscosity of a dilute suspension of nanoplatelets with slip. We find a non-monotonic variation of this term, with a minimum occurring when the slip length is comparable to the thickness of the particle.","tags":null,"title":"Effect of hydrodynamic slip on the rotational dynamics of a thin Brownian platelet in shear flow","type":"publication"},{"authors":["**Simon Gravelle**","Catherine Kamal","Lorenzo Botto"],"categories":null,"content":"","date":1616716800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1616716800,"objectID":"c9b43379e5a74a23273e30f0fd14b978","permalink":"https://simongravelle.github.io/publication/2021-violations-of-jeffery.html","publishdate":"2021-03-26T00:00:00Z","relpermalink":"/publication/2021-violations-of-jeffery.html","section":"publication","summary":"Using molecular dynamics simulations we investigate the shear-induced rotational dynamics of a Brownian nanographene (hexabenzocoronene) freely suspended in a liquid. We demonstrate that, owing to a finite hydrodynamic slip at the molecular surface, these flat molecules tend to align with a constant orientation angle instead of performing the classical periodic orbits predicted by Jeffery's theory. Results are extracted for different Péclet numbers and compared to the predictions by a theory developed for a rigid axisymmetric particle with orientation confined to the flow-gradient plane. The theory is based on the resolution of a one-dimensional Fokker-Planck equation for the angle φ made by one of the particle's diameters with the flow direction. Remarkably, our results show that the essential features of the three-dimensional orientational statistics of the nanographene are captured by the one-dimensional model, given that the hydrodynamic velocity is closed in terms of the slip length λ. Finally, we explore the situation in which multiple nanographenes are suspended in the liquid, and show that slip results in a reduction in specific viscosity.","tags":null,"title":"Violations of Jeffery's theory in the dynamics of nanographene in shear flow","type":"publication"},{"authors":["Catherine Kamal","**Simon Gravelle**","Lorenzo Botto"],"categories":null,"content":"","date":1584576e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1584576e3,"objectID":"f3f6ddd983096bc3445a23c3fd37d9f0","permalink":"https://simongravelle.github.io/publication/2020-hydrodynamic-slip-can-align.html","publishdate":"2020-03-19T00:00:00Z","relpermalink":"/publication/2020-hydrodynamic-slip-can-align.html","section":"publication","summary":"The large-scale processing of nanomaterials such as graphene and MoS2 relies on understanding the flow behaviour of nanometrically-thin platelets suspended in liquids. Here we show, by combining non-equilibrium molecular dynamics and continuum simulations, that rigid nanoplatelets can attain a stable orientation for sufficiently strong flows. Such a stable orientation is in contradiction with the rotational motion predicted by classical colloidal hydrodynamics. This surprising effect is due to hydrodynamic slip at the liquid-solid interface and occurs when the slip length is larger than the platelet thickness; a slip length of a few nanometers may be sufficient to observe alignment. The predictions we developed by examining pure and surface-modified graphene is applicable to different solvent/2D material combinations. The emergence of a fixed orientation in a direction nearly parallel to the flow implies a slip-dependent change in several macroscopic transport properties, with potential impact on applications ranging from functional inks to nanocomposites.","tags":null,"title":"Hydrodynamic slip can align thin nanoplatelets in shear flow","type":"publication"},{"authors":["**Simon Gravelle**","Catherine Kamal","Lorenzo Botto"],"categories":null,"content":"","date":1583712e3,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1583712e3,"objectID":"b50bc032d4d61cb2ce09c926836ba105","permalink":"https://simongravelle.github.io/publication/2020-liquid-exfoliation.html","publishdate":"2020-03-09T00:00:00Z","relpermalink":"/publication/2020-liquid-exfoliation.html","section":"publication","summary":"Liquid-phase exfoliation, the use of a sheared liquid to delaminate graphite into few-layer graphene, is a promising technique for the large-scale production of graphene. However, the microscale and nanoscale fluid-structure processes controlling the exfoliation are not fully understood. Here, we perform non-equilibrium molecular dynamics simulations of a defect-free graphite nanoplatelet suspended in a shear flow and measure the critical shear rate γ̇ c needed for the exfoliation to occur. We compare γ̇ c for different solvents, including water and N-methyl-pyrrolidone, and nanoplatelets of different lengths. Using a theoretical model based on a balance between the work done by viscous shearing forces and the change in interfacial energies upon layer sliding, we are able to predict the critical shear rates γ̇ c measured in simulations. We find that an accurate prediction of the exfoliation of short graphite nanoplatelets is possible only if both hydrodynamic slip and the fluid forces on the graphene edges are considered and if an accurate value of the solid–liquid surface energy is used. The commonly used “geometric-mean” approximation for the solid–liquid energy leads to grossly incorrect predictions.","tags":null,"title":"Liquid exfoliation of multilayer graphene in sheared solvents: A molecular dynamics investigation","type":"publication"},{"authors":["Pascal Raux","**Simon Gravelle**","Jacques Dumais"],"categories":null,"content":"","date":1579478400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1579478400,"objectID":"06a6b0593fbff727788d83e679c6d1f4","permalink":"https://simongravelle.github.io/publication/2020-design-of-a-unidirectional.html","publishdate":"2020-01-20T00:00:00Z","relpermalink":"/publication/2020-design-of-a-unidirectional.html","section":"publication","summary":"The bromeliad Tillandsia landbeckii thrives in the Atacama desert of Chile using the fog captured by specialized leaf trichomes to satisfy its water needs. However, it is still unclear how the trichome of T. landbeckii and other Tillandsia species is able to absorb fine water droplets during intermittent fog events while also preventing evaporation when the plant is exposed to the desert’s hyperarid conditions. Here, we explain how a 5800-fold asymmetry in water conductance arises from a clever juxtaposition of a thick hygroscopic wall and a semipermeable membrane. While absorption is achieved by osmosis of liquid water, evaporation under dry external conditions shifts the liquid-gas interface forcing water to diffuse through the thick trichome wall in the vapor phase. We confirm this mechanism by fabricating artificial composite membranes mimicking the trichome structure. The reliance on intrinsic material properties instead of moving parts makes the trichome a promising basis for the development of microfluidics valves.","tags":null,"title":"Design of a unidirectional water valve in Tillandsia","type":"publication"},{"authors":["**Simon Gravelle**","Jacques Dumais"],"categories":null,"content":"","date":1578009600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1578009600,"objectID":"1dadce7b7ecdb6ddee779b7741a147fa","permalink":"https://simongravelle.github.io/publication/2020-a-multi-scale-model.html","publishdate":"2020-01-03T00:00:00Z","relpermalink":"/publication/2020-a-multi-scale-model.html","section":"publication","summary":"Tillandsia landbeckii is a rootless plant thriving in the hyper-arid Atacama Desert of Chile. These plants use unique cellulose-based microscopic structures called trichomes to collect fresh water from coastal fog. The trichomes rely on a passive mechanism to maintain an asymmetrical transport of water: they allow for the fast absorption of liquid water deposited by sporadic fog events while preventing evaporation during extended drought periods. Inspired by the trichome’s design, we study fluid transport through a micrometric valve. Combining Grand Canonical Monte Carlo with Non-Equilibrium Molecular Dynamics simulations, we first analyze the adsorption and transport of a fluid through a single nanopore at different chemical potentials. We then scale up the atomic results using a lattice approach, and simulate the transport at the micrometric scale. Results obtained for a model Lennard-Jones fluid and TIP4P/2005 water were compared, allowing us to identify the key physical parameters for achieving a passive hydraulic valve. Our results show that the difference in transport properties of water vapor and liquid water within the cellulose layer is the basis for the ability of the Tillandsia trichome to function as a water valve. Finally, we predict a critical pore dimension above which the cellulose layer can form an efficient valve.","tags":null,"title":"A multi-scale model for fluid transport through a bio-inspired passive valve","type":"publication"},{"authors":["**Simon Gravelle**","Christophe Ybert"],"categories":null,"content":"","date":1577404800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1577404800,"objectID":"a21fb854e4f6fa2120e0dcc5ceb8f248","permalink":"https://simongravelle.github.io/publication/2019-flow-induced.html","publishdate":"2019-12-27T00:00:00Z","relpermalink":"/publication/2019-flow-induced.html","section":"publication","summary":"Despite mass flow being arguably the most elementary transport associated with nanofluidics, its measurement still constitutes a significant bottleneck for the development of this promising field. Here, we investigate how a liquid flow perturbs the ubiquitous enrichment—or depletion—of a solute inside a single nanochannel. Using fluorescence correlation spectroscopy to access the local solute concentration, we demonstrate that the initial enrichment—the so-called Donnan equilibrium—is depleted under flow, thus revealing the underlying mass transport. Combining theoretical and numerical calculations beyond the classical 1D treatment of nanochannels, we rationalize quantitatively our observations and demonstrate unprecedented flow rate sensitivity. Because the present mass transport investigations are based on generic effects, we believe that they can develop into a versatile approach for nanofluidics.","tags":null,"title":"Flow-induced shift of the Donnan equilibrium for ultra-sensitive mass transport measurement through a single nanochannel","type":"publication"},{"authors":["**Simon Gravelle**","Roland R. Netz","Lydéric Bocquet"],"categories":null,"content":"","date":1567123200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1567123200,"objectID":"5b6c563e7db3679adbfc53451aaae974","permalink":"https://simongravelle.github.io/publication/2019-adsorption-kinetics.html","publishdate":"2019-08-30T00:00:00Z","relpermalink":"/publication/2019-adsorption-kinetics.html","section":"publication","summary":"Ionic current measurements through solid-state nanopores consistently show a power spectral density that scales as 1/f α at low frequency f, with an exponent α ∼ 0.5–1.5, but strikingly, the physical origin of this behavior remains elusive. Here, we perform simulations of particles reversibly adsorbing at the surface of a nanopore and show that the fluctuations in the number of adsorbed particles exhibit low-frequency pink noise. We furthermore propose theoretical modeling for the time-dependent adsorption of particles on the nanopore surface for various geometries, which predicts a frequency spectrum in very good agreement with the simulation results. Altogether, our results highlight that the low-frequency noise takes its origin in the reversible adsorption of ions at the pore surface combined with the long-lasting excursions of the ions in the reservoirs. The scaling regime of the power spectrum extends down to a cutoff frequency which is far smaller than simple diffusion estimates. Using realistic values for the pore dimensions and the adsorption–desorption kinetics, this predicts the observation of pink noise for frequencies down to the hertz for a typical solid-state nanopore, in good agreement with experiments.","tags":null,"title":"Adsorption Kinetics in Open Nanopores as a Source of Low-Frequency Noise","type":"publication"},{"authors":["Lyderic Bocquet","Alessandro Siria","Benoit Laborie","Hiroaki Yoshida","Simon Gravelle"],"categories":null,"content":"","date":1490572800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1490572800,"objectID":"69861247e11c1c15342b4db861d37d43","permalink":"https://simongravelle.github.io/publication/2016-use-of-nanoporous.html","publishdate":"2017-03-27T00:00:00Z","relpermalink":"/publication/2016-use-of-nanoporous.html","section":"publication","summary":"The invention relates to the extraction of organic compounds from mixtures of said compounds with water, using a nanoporous carbon membrane. The invention can be used in any field where it is desired to separate an organic compound of interest from water, such as the drying of alcohols or alkanes.","tags":null,"title":"Use of nanoporous carbon membranes for separating aqueous/organic mixtures","type":"publication"},{"authors":["**Simon Gravelle**","Hiroaki Yoshida","Laurent Joly","Christophe Ybert","Lydéric Bocquet"],"categories":null,"content":"","date":1474934400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1474934400,"objectID":"85e25b5671220294508f558d2cb86e70","permalink":"https://simongravelle.github.io/publication/2016-carbon-membrane.html","publishdate":"2016-09-27T00:00:00Z","relpermalink":"/publication/2016-carbon-membrane.html","section":"publication","summary":"We demonstrate, on the basis of molecular dynamics simulations, the possibility of an efficient water-ethanol separation using nanoporous carbon membranes, namely, carbon nanotube membranes, nanoporous graphene sheets, and multilayer graphene membranes. While these carbon membranes are in general permeable to both pure liquids, they exhibit a counter-intuitive “self-semi-permeability” to water in the presence of water-ethanol mixtures. This originates in a preferred ethanol adsorption in nanoconfinement that prevents water molecules from entering the carbon nanopores. An osmotic pressure is accordingly expressed across the carbon membranes for the water-ethanol mixture, which agrees with the classic van’t Hoff type expression. This suggests a robust and versatile membrane-based separation, built on a pressure-driven reverse-osmosis process across these carbon-based membranes. In particular, the recent development of large-scale “graphene-oxide” like membranes then opens an avenue for a versatile and efficient ethanol dehydration using this separation process, with possible application for bio-ethanol fabrication.","tags":null,"title":"Carbon membranes for efficient water-ethanol separation","type":"publication"},{"authors":["Adrien Guérin","**Simon Gravelle**","Lydéric Bocquet"],"categories":null,"content":"","date":1468972800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1468972800,"objectID":"7633fb7583f59073d092204e0fea3327","permalink":"https://simongravelle.github.io/publication/2016-forces-behind.html","publishdate":"2016-07-20T00:00:00Z","relpermalink":"/publication/2016-forces-behind.html","section":"publication","summary":"The cell theory developed in the early 19th century teaches us that only cells beget cells (1). As a consequence, the evolution of life on Earth is but a long sequence of cell divisions; wherever this sequence is broken, life ends. Cell division is not only how organisms perpetuate themselves, it is also one way in which complexity is built during development. The contribution of cell division to development is particularly striking in plants because plant cells are surrounded by stiff walls, making them clearly distinguishable from each other and fixing their spatial relation by preventing cell migration (...)","tags":null,"title":"Forces behind plant cell division","type":"publication"},{"authors":["**Simon Gravelle**","Christophe Ybert","Lydéric Bocquet","Laurent Joly"],"categories":null,"content":"","date":1458777600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1458777600,"objectID":"3b047b9bda6e6c46ff94f2c17e7eb74b","permalink":"https://simongravelle.github.io/publication/2016-anomalous-capillary.html","publishdate":"2016-03-24T00:00:00Z","relpermalink":"/publication/2016-anomalous-capillary.html","section":"publication","summary":"This work revisits capillary filling dynamics in the regime of nanometric to subnanometric channels. Using molecular dynamics simulations of water in carbon nanotubes, we show that for tube radii below one nanometer, both the filling velocity and the Jurin rise vary nonmonotonically with the tube radius. Strikingly, with fixed chemical surface properties, this leads to confinement-induced reversal of the tube wettability from hydrophilic to hydrophobic for specific values of the radius. By comparing with a model liquid metal, we show that these effects are not specific to water. Using complementary data from slit channels, we then show that they can be described using the disjoining pressure associated with the liquid structuring in confinement. This breakdown of the standard continuum framework is of main importance in the context of capillary effects in nanoporous media, with potential interests ranging from membrane selectivity to mechanical energy storage.","tags":null,"title":"Anomalous capillary filling and wettability reversal in nanochannels","type":"publication"},{"authors":["**Simon Gravelle**"],"categories":null,"content":"","date":1456790400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1456790400,"objectID":"95db3f45aa3ce1e77f82a5daef778878","permalink":"https://simongravelle.github.io/publication/2015-nanofluidics-a-pedagogical.html","publishdate":"2016-03-01T00:00:00Z","relpermalink":"/publication/2015-nanofluidics-a-pedagogical.html","section":"publication","summary":"Nanofluidics is the study of fluids confined in structures of nanometric dimensions (typically 1 − 100 nm). Fluids confined in these structures exhibit behaviours that are not observed in larger structures, due to a high surface to bulk ratio (...)","tags":null,"title":" Nanofluidics: a pedagogical introduction ","type":"publication"},{"authors":["**Simon Gravelle**"],"categories":null,"content":"","date":1447718400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1447718400,"objectID":"d48b275814aabf96eed8441d234f416c","permalink":"https://simongravelle.github.io/publication/2015-nanofluidics-a-theoretical.html","publishdate":"2015-11-17T00:00:00Z","relpermalink":"/publication/2015-nanofluidics-a-theoretical.html","section":"publication","summary":"Nanofluidics is the study of fluids confined in structures of nanometric dimensions (typically 1 − 100 nm). Fluids confined in these structures exhibit behaviours that are not observed in larger structures, due to a high surface to bulk ratio (...)","tags":null,"title":"Nanofluidics: a theoretical and numerical investigation of fluid transport in nanochannels","type":"publication"},{"authors":["**Simon Gravelle**","Laurent Joly","François Detcheverry","Christophe Ybert","Cécile Cottin-Bizonne","Lydéric Bocquet"],"categories":null,"content":"","date":1425427200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1425427200,"objectID":"41d6459fc279c1e47b30edf7bff5f2f0","permalink":"https://simongravelle.github.io/publication/2015-permeabilite-optimale.html","publishdate":"2015-03-04T00:00:00Z","relpermalink":"/publication/2015-permeabilite-optimale.html","section":"publication","summary":"Les aquaporines sont des protéines transmembranaires omniprésentes dans le corps humain. Insérées dans les membranes cellulaires, elles jouent un rôle important dans la filtration, l’absorption et la sécrétion des fluides. L’excellent compromis entre sélectivité et perméabilité à l’eau des aquaporines reste mal compris aujourd’hui. Dans ce travail, nous nous intéressons à la forme en sablier des aquaporines, dont nous étudions l’influence sur la perméabilité, à l’aide de calculs numériques et d’un modèle théorique simple. Nous montrons qu’il existe un angle d’ouverture optimal qui maximise la perméabilité, et dont la valeur est proche des angles observés dans les aquaporines.","tags":null,"title":"Perméabilité optimale des aquaporines : une histoire de forme?","type":"publication"},{"authors":["**Simon Gravelle**","Laurent Joly","Christophe Ybert","Lydéric Bocquet"],"categories":null,"content":"","date":1412812800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1412812800,"objectID":"332b41c66c17a5ecadd631be711e12ea","permalink":"https://simongravelle.github.io/publication/2014-large-permeabilities.html","publishdate":"2014-10-09T00:00:00Z","relpermalink":"/publication/2014-large-permeabilities.html","section":"publication","summary":"In fluid transport across nanopores, there is a fundamental dissipation that arises from the connection between the pore and the macroscopic reservoirs. This entrance effect can hinder the whole transport in certain situations, for short pores and/or highly slipping channels. In this paper, we explore the hydrodynamic permeability of hourglass shape nanopores using molecular dynamics (MD) simulations, with the central pore size ranging from several nanometers down to a few Angströms. Surprisingly, we find a very good agreement between MD results and continuum hydrodynamic predictions, even for the smallest systems undergoing single file transport of water. An optimum of permeability is found for an opening angle around 5°, in agreement with continuum predictions, yielding a permeability five times larger than for a straight nanotube. Moreover, we find that the permeability of hourglass shape nanopores is even larger than single nanopores pierced in a molecular thin graphene sheet. This suggests that designing the geometry of nanopores may help considerably increasing the macroscopic permeability of membranes.","tags":null,"title":"Large permeabilities of hourglass nanopores: From hydrodynamics to single file transport","type":"publication"},{"authors":["Alessandro Gadaleta","Catherine Sempere","**Simon Gravelle**","Alessandro Siria","Rémy Fulcrand","Christophe Ybert","Lydéric Bocquet"],"categories":null,"content":"","date":1391126400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1391126400,"objectID":"49777b08f28d3a441a4d069a4b46dfe8","permalink":"https://simongravelle.github.io/publication/2014-sub-additive.html","publishdate":"2014-01-31T00:00:00Z","relpermalink":"/publication/2014-sub-additive.html","section":"publication","summary":"Nanopores, either biological, solid-state, or ultrathin pierced graphene, are powerful tools which are central to many applications, from sensing of biological molecules to desalination and fabrication of ion selective membranes. However, the interpretation of transport through low aspect-ratio nanopores becomes particularly complex as 3D access effects outside the pores are expected to play a dominant role. Here, we report both experiments and theory showing that, in contrast to naïve expectations, long-range mutual interaction across an array of nanopores leads to a non-extensive, sub-linear scaling of the global conductance on the number of pores N. A scaling analysis demonstrates that the N-dependence of the conductance depends on the topology of the network. It scales like G ∼ N/log N for a 1D line of pores, and like G∼N−−√ for a 2D array, in agreement with experimental measurements. Our results can be extended to alternative transport phenomena obeying Laplace equations, such as diffusive, thermal, or hydrodynamic transport. Consequences of this counter-intuitive behavior are discussed in the context of transport across thin membranes, with applications in energy harvesting.","tags":null,"title":"Sub-additive ionic transport across arrays of solid-state nanopores","type":"publication"},{"authors":["Clara Picallo","**Simon Gravelle**","Laurent Joly","Elisabeth Charlaix","Lydéric Bocquet"],"categories":null,"content":"","date":138672e4,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":138672e4,"objectID":"39b299f33f1e3af97aeef633de84ff41","permalink":"https://simongravelle.github.io/publication/2013-nanofluidic-osmotic.html","publishdate":"2013-12-11T00:00:00Z","relpermalink":"/publication/2013-nanofluidic-osmotic.html","section":"publication","summary":"Osmosis describes the flow of water across semipermeable membranes powered by the chemical free energy extracted from salinity gradients. While osmosis can be expressed in simple terms via the van ’t Hoff ideal gas formula for the osmotic pressure, it is a complex phenomenon taking its roots in the subtle interactions occurring at the scale of the membrane nanopores. Here we use new opportunities offered by nanofluidic systems to create an osmotic diode exhibiting asymmetric water flow under reversal of osmotic driving. We show that a surface charge asymmetry built on a nanochannel surface leads to nonlinear couplings between water flow and the ion dynamics, which are capable of water flow rectification. This phenomenon opens new opportunities for water purification and complex flow control in nanochannels.","tags":null,"title":"Nanofluidic osmotic diodes: Theory and molecular dynamics simulations","type":"publication"},{"authors":["**Simon Gravelle**","Laurent Joly","François Detcheverry","Christophe Ybert","Cécile Cottin-Bizonne","Lydéric Bocquet"],"categories":null,"content":"","date":1380067200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1380067200,"objectID":"966c17ea8b9020cf61760b49d2106003","permalink":"https://simongravelle.github.io/publication/2012-optimizing-water.html","publishdate":"2013-09-25T00:00:00Z","relpermalink":"/publication/2012-optimizing-water.html","section":"publication","summary":"Aquaporin channels are able to selectively conduct water across cell membranes, with remarkable efficiency. Although molecular details are crucial to the pore performance, permeability is also strongly limited by viscous dissipation at the entrances. Could the hourglass shape of aquaporins optimize such entrance effects? We show that conical entrances with suitable opening angle can indeed provide a large increase of the channel permeability. Strikingly, the optimal opening angles compare well with the angles measured in a large variety of aquaporins, suggesting that their hourglass shape could be the result of a natural selection process toward optimal permeability. This work also provides guidelines to optimize the performances of artificial nanopores, with applications in desalination, ultrafiltration, or energy conversion.","tags":null,"title":"Optimizing water permeability through the hourglass shape of aquaporins","type":"publication"}]
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