Roland J-M Pellenq

• PhD
• Director of Research at CNRS-Université de Montpellier

This study investigates the dynamic behavior of aqueous electrolytes in porous carbon electrodes under voltage, with a focus on the impact of electrode flexibility on the pore texture. Utilizing a constant-voltage approach with a reactive interaction potential, we examine the heterogeneous charge distribution on carbon atoms within the electrode, r...

The mechanical properties of clay minerals are largely dependent upon the chemical compositions and the mesoscale fabrics of the constituent particles. This paper describes results of a series of mesoscale molecular dynamics simulations of the hydrostatic compression and shear strain behavior for initially randomly oriented assemblies of 10³ illite...

CO 2 mineralization, a process where CO 2 reacts with minerals to form stable carbonates, presents a sustainable approach for CO 2 sequestration and mitigation of global warming. While the crucial role of water in regulating CO 2 mineralization efficiency is widely acknowledged, a comprehensive understanding of the underlying mechanisms remains elu...

The carbonation reaction is essential in the global carbon cycle and in the carbon dioxide (CO2) capture. In oceans (pH 8.1) or in synthetic materials such as cement or geopolymers (pH over 12), the basic pH conditions affect the reaction rate of carbonation. However, the precipitation of calcium or magnesium carbonates acidifies the environment an...

Although widely studied experimentally in the 1990s, the structure and properties of low-dimensional or high-pressure phases of fullerenes have recently been re-examined. Remarkably, recent experiments have shown that transparent, nearly pure amorphous sp³-bonded carbon phases can be obtained by heating a C60 molecular crystal at a high pressure. W...

While the MgCl2 mixing alite paste causes degradation of the modulus and hardness of C–S–H formed, the underlying degradation mechanism needs to be better understood. This study comprehensively analyzed the mechanical properties of alite pastes mixed with MgCl2 solutions, examining the effects at both mesoscale and nanoscale. The in situ X‐ray diff...

The mechanical properties of clay minerals are largely dependent upon the chemical compositions and the mesoscale fabrics of the constituent particles. This paper describes results of a series of mesoscale molecular dynamics simulations of the hydrostatic compression and shear strain behavior for initially randomly-oriented assemblies of 10 3 Illit...

In the present study, polycrystalline films of layered zinc phosphate hydrate are produced by a facile, low‐temperature single‐step hydrothermal fabrication method on top of Cu metal substrates. Despite containing structural water, the as‐grown films remain crystalline, chemically stable, and electrically conductive. The photoluminescence spectrum...

The Oak Ridge National Laboratory is planning to build the Second Target Station (STS) at the Spallation Neutron Source (SNS). STS will host a suite of novel instruments that complement the First Target Station's beamline capabilities by offering an increased flux for cold neutrons and a broader wavelength bandwidth. A novel neutron imaging beamlin...

We present results of a hybrid analytical-simulation investigation of the fracture resistance of heterogeneous materials. We show that bond-energy fluctuations sampled by Monte Carlo simulations in the semigrand canonical ensemble provide a means to rationalize the complexity of heterogeneous fracture processes, encompassing probability and percola...

Bottom-up modeling of clay behavior from the molecular scale requires a detailed understanding of the free energy between pairs of clay platelets. We investigate the potential of mean force (PMF) for hydrated clays in face-to-face interactions with free energy perturbation (FEP) methods through molecular dynamics simulations using simple overlap sa...

One of the major challenges of the 21st century world is defined by its growing population. Accompanied by urbanization and changing climate, humanity is going to be exposed to severe sustainability and resilience challenges. Exposure to extreme weather events, intensified environmental risks, health burdens, or scarcity of natural resources due to...

We present a mechanistic model of carbon nucleation and growth from a fluid at elevated temperature (T) and pressure conditions, typical of those found in the shallow Earth’s lithosphere. Our model uses a replica exchange reactive molecular dynamics framework in which molecular configurations are swapped between adjacent T replica at regular interv...

Ion specificity and related Hofmeister effects, which are ubiquitous in aqueous systems, can have spectacular consequences in hydrated clays, where ion-specific nanoscale surface forces can determine large-scale cohesive swelling and shrinkage behaviors of soil and sediments. We have used a semiatomistic computational approach and examined sodium,...

Human health in urban environment has emerged as a primary focus of sustainable development during the time of global pandemic caused by a severe acute respiratory syndrome due to the SARS-CoV-2 coronavirus, COVID-19. It has reshaped the world with the way our communities interact, people work, commute, and spend their leisure time. While different...

Significance Nanoporous carbon texture makes fundamental understanding of the electrochemical processes challenging. Based on density functional theory (DFT) results, the proposed atomistic approach takes into account topological and chemical defects of the electrodes and attributes to them a partial charge that depends on the applied voltage. Usin...

The precipitation of zeolite nanoparticles involves the initial formation of metastable precursors, such as amorphous entities, that crystallize through non-classical pathways. Here, using reactive force field-based simulations, we reveal how aluminosilicate oligomers grow concomitantly to the decondensation of silicate entities during the initial...

Ion specificity and related Hofmeister effects, ubiquitous in aqueous systems, can have spectacular consequences in hydrated clays, where ion-specific nanoscale surface forces can determine large scale cohesive, swelling and shrinkage behaviors of soil and sediments. We have used a semi-atomistic computational approach and examined sodium, calcium...

Understanding the formation of Alkali-silica reaction gel (ASR gel) and its behavior in cement pore network solutions is the key to mitigate one of the main causes of the strength retrogression of concrete. We herein propose a scenario to explain how ASR formation in cement pores can damage the cement paste structure that is supported by state-of-t...

From soft polymeric gels to hardened cement paste, amorphous solids under constant load exhibit a pronounced time-dependent deformation called creep. The microscopic mechanism of such a phenomenon is poorly understood in amorphous materials and constitutes an even greater challenge in densely packed and chemically reactive granular systems. Both fe...

Freezing in charged porous media can induce significant pressure and cause damage to tissues and functional materials. We formulate a thermodynamically consistent theory to model freezing phenomena inside charged heterogeneous porous space. Two regimes are distinguished: free ions in open pore space lead to negligible effects of freezing point depr...

Cement is one of the most produced materials in the world. A major player in greenhouse gas emissions, it is the main binding agent in concrete, to which it provides a cohesive strength that rapidly increases during setting. Understanding how such cohesion emerges has been a major obstacle to advances in cement science and technology. Here, we comb...

Cement is the most produced material in the world. A major player in greenhouse gas emissions, it is the main binding agent in concrete, providing a cohesive strength that rapidly increases during setting. Understanding how such cohesion emerges is a major obstacle to advances in cement science and technology. Here, we combine computational statist...

A significant part of the hydrocarbons contained in source rocks remains confined within the organic matter -called kerogen- from where they are generated. Understanding the sorption and transport properties of confined hydrocarbons within the kerogens is, therefore, paramount to predict production. Specifically, knowing the impact of thermal matur...

We present a simulation method to assess the quasistatic fracture resistance of materials. Set within a semi-grand-canonical Monte Carlo (SGCMC) simulation environment, an auxiliary field—the bond rupture potential—is introduced to generate a sufficiently large number of possible microstates in the semi-grand-canonical ensemble, and associated ener...

A remarkable variety of organisms and wet materials are able to endure temperatures far below the freezing point of bulk water. Cryotolerance in biology is usually attributed to “antifreeze” proteins, and yet massive supercooling (<−40∘C) is also possible in porous media containing only simple aqueous electrolytes. For concrete pavements, the commo...

The fluid flow through porous media is described by Darcy's law, while the fluid/wall interactions can be neglected. In nanopores, where adsorption dominates, Darcy's extension has been made, but approaches able to describe flows in mesopores are still lacking. We show here that molecular flows through nano-constrictions is well described by Berver...

Utilizing a 3D mean-field lattice-gas model, we analyze the effect of confinement on the nature of capillary phase transition in granular aggregates with varying disorder and their inverse porous structures obtained by interchanging particles and pores. Surprisingly, the confinement effects are found to be much less pronounced in granular aggregate...

Utilizing a 3D mean-field lattice-gas model, we analyze the effect of confinement on the nature of capillary phase transition in granular aggregates with varying disorder and their inverse porous structures obtained by interchanging particles and pores. Surprisingly, the confinement effects are found to be much less pronounced in granular aggregate...

From soft polymeric gels to hardened cement paste, amorphous solids under constant load exhibit pronounced time-dependent deformations called creep. The microscopic mechanism of such a phenomenon is poorly understood and constitutes a significant challenge in densely packed and chemically aging granular systems. Both features are prominently presen...

Methane diffusion in micro- and mesopores of carbonaceous materials is dominated by molecular interactions with the pore walls. As a consequence, the fluid molecules are mainly in a diffusive regime and the laws of fluid mechanics are not directly applicable. A method called the "free volume theory" has been successfully used by different authors t...

During cement hydration, C-S-H nanoparticles precipitate and form a porous and heterogeneous gel that glues together the hardened product. C-S-H nucleation and growth is driven by dissolution of the cement grains, posing the question of how cement grain surfaces induce spatial heterogeneities in the formation of C-S-H and affect the overall microst...

The 13C NMR chemical shifts corresponding to different sites in atomistic models of disordered carbons were computed at different H contents by employing DFT calculations. Structural models were generated by molecular dynamics simulations and validated by the pair distribution functions; further bonding analyses were carried out to determine the am...

Recent accelerated simulations of the decondensation of silicates by sodium hydroxide open a window on understanding complex mechanisms of depolymerization of silicate chains. Herein, complex mechanisms of decondensation, that involve two water molecules (or OH$^-$ groups) are unveiled. The study of two different solutions, having the same chemical...

Macroscopic mechanical properties of materials depend directly on their microstructure. Microscopy, and more specifically tomography, is a key method for studying microstructures. Here, we propose a simple way to use an X-ray tomogram to infer local elastic properties. We distinguish between two scenarios of microstructure images. In the first scen...

Urban heat island (UHI) is a climate effect that magnifies air temperature in cities. In the US it affects over 80% of the population and in general is considered an adverse phenomenon with externalities ranging from increased air pollution to higher energy demand and deteriorated human comfort. Therefore, UHI and its mitigation strategies have bee...

Silica is by far the chemical compound the most widespread and used around the world: as a raw product in the buildings and roads industry, as concrete, or as a processed product in the manufacture of glass, ceramics or zeolites. In alkali silicate solutions—often used to synthesize those materials—a complex interplay of decondensation and condensa...

While shale gas has become a major source of energy, a more sustainable recovery requires better understanding of the gas/kerogen matrix interactions. Here we use replica exchange molecular dynamics to investigate the geological conversion of two important classes of gas-forming organic matter: lignin and cellulose. In agreement with results from p...

Reactive molecular dynamics (MD) simulations, especially those employing acceleration techniques, can provide useful insights on the mechanism underlying the transformation of buried organic matter, yet, so far, it remains extremely difficult to predict the time scales associated with these processes at moderate temperatures (i.e., when such time s...

We analyze the packing properties of simulated three-dimensional polydisperse samples of spherical particles assembled by mechanical compaction with zero interparticle friction, leading to random close-packed configurations of the highest packing fraction. The particle size distributions are generated from the incomplete beta distribution with thre...

Freezing in charged porous media can induce significant pressure and cause damage to tissues and functional materials. We formulate a thermodynamically consistent theory to model freezing phenomena inside charged heterogeneous porous space. Two regimes are distinguished: free ions in open pore space lead to negligible effects of freezing point depr...

The aggregation of colloidal clay mineral particles plays an important role in controlling the mechanical and transport properties of soils. Interactions and aggregation of plate-like montmorillonite particles were previously studied with the help of Molecular Dynamics (MD) simulation. This paper investigates the aggregation of cylindrical imogolit...

In order to get insight into the wet agglomeration process, we numerically investigate the growth of a single granule inside a dense flow of an initially homogeneous distribution of wet and dry particles. The simulations are performed by means of the discrete element method and the binding liquid is assumed to be transported by the wet particles, w...

The formation and ageing of gels is a complex issue that has to be resolved to investigate manifold synthetic materials, among them: porous materials such as cement, high-quality glass fiber, and geomaterials for radioactive waste sealing. Herein, a coupling between a grand canonical Monte Carlo and the parallel tempering methods is developed. The...

It has been recognized that the microporosity of shales organic matter, called kerogen, strongly affects the hydrocarbon recovery process from unconventionnal reservoirs. So far, the numerical studies on hydrocarbon transport through the microporous phase of kerogen have neglected the effect of poromechanics, i.e. the adsorption-induced deformation...

Capillary effects such as imbibition-drying cycles impact the mechanics of granular systems over time. A multiscale poromechanics framework was applied to cement paste, that is the most common building material, experiencing broad humidity variations over the lifetime of infrastructure. First, the liquid density distribution at intermediate to high...

A remarkable variety of organisms and wet materials are able to endure temperatures far below the freezing point of bulk water. Cryo-tolerance in biology is usually attributed to "anti-freeze" proteins, and yet massive supercooling ($< -40^\circ$C) is also possible in porous media containing only simple aqueous electrolytes. For concrete pavements,...

Significance Capillary effects in cement paste are associated with multiple degradation mechanisms. Using a framework, we investigated the role of capillary forces in cement paste under partial saturation from the nanograins level to the mesoscale. We show that the largest capillary forces concentrate at the boundary between gel pores and larger ca...

In order to get insight into wet agglomeration process, we numerically investigate the growth of a single granule inside a dense flow of an initially homogeneous distribution of wet and dry particles. The simulations are performed by means of the discrete-element method and the binding liquid is assumed to be transported by the wet particles, which...

Fragility curves represent a structure’s likelihood of damage under a range of load levels—like those from natural hazards. They, therefore, help to set building code safety factors, resiliency ratings, and even insurance premiums. Unfortunately, there is no real standard for generating these fragility curves for wind loading. FEMA’s HAZUS hurrican...

Alkali-silica-reaction (ASR) is a significant cause of premature concrete deterioration. Although it has received much research attention, an essential question still remains—how does a soft gel, as is formed by this reaction, induce the critical level of stress to exceed the strength of, and crack the concrete matrix? One possibility is that the A...

Windstorms currently generate $28 billion in average annual damage and this figure is projected to potentially rise to $38 billion by 2075. Traditional engineering approaches that analyze the resilience of structures fail to account for non-structural damage because of the difficulties in modeling such damage. Additionally, even detailed frameworks...

Freeze-thaw (FT) damage is a significant threat to roads and pavement, yet the underlying mechanism is still unclear. Conventional thinking attributes the damage to pressure generated by expansion of water upon freezing. However, this idea fails to explain three phenomena: 1) only above a critical degree of water saturation will FT damage occur; 2)...

Built on the framework of effective interaction potentials using lattice element method, a methodology to calibrate and to validate the elasticity of solid constituents in heterogeneous porous media from experimentally measured nanoindentation moduli and imported scans from advanced imaging techniques is presented. Applied to computed tomography (C...

Significance In source rocks, natural hydrocarbons are generated from organic matter dispersed in a fine-grained mineral matrix. The potential recovery of hydrocarbons is therefore influenced by the geometry of the organic hosted porous networks. Here, the three-dimensional structures of such networks are revealed using electron tomography with a s...

Fragility curves, which are a statistical tool that represent the probability of exceeding a certain level of structural damage due to various forces applied to a building, are used to assess anticipated building performance. For new construction and retrofitting alike, designers and builders need to understand the risks their buildings face from e...

Whilst hydrocarbon expulsion from kerogen is certainly the key step in shale oil/gas recovery, the poromechanical couplings governing this desorption process, taking place under a significant pressure gradient, are still poorly understood. Especially, most molecular simulation investigations of hydrocarbon adsorption and transport in kerogen have s...

This article presents a nonequilibrium thermodynamic theory for the mean-field precipitation, aggregation, and pattern formation of colloidal clusters. A variable gradient energy coefficient and the arrest of particle diffusion upon “jamming” of cluster aggregates in the spinodal region predicts observable gel patterns that, at high intercluster at...

This Article presents a nonequilibrium thermodynamic theory for the mean-field precipitation, aggregation and pattern formation of colloidal clusters. A variable gradient energy coefficient and the arrest of particle diffusion upon "jamming" of cluster aggregates in the spinodal region predicts observable gel patterns that, at high inter-cluster at...

Cement paste is a multiphase material of complex chemistry, of which 60% by volume is typically composed of calcium–silicate–hydrates (C–S–H), the phase that lends the material its strength and stiffness. Moreover, it has been shown that the C–S–H phase is a dispersion of nanometer-sized particles that are characterized by an attractive–repulsive p...

An atomistic and mesoscopic assessment of the effect of alkali uptake in cement paste is performed. Semi-grand canonical Monte Carlo simulations indicate that Na and K not only adsorb at the pore surface of calcium silicate hydrates (C-S-H) but also adsorb in the C-S-H hydrated interlayer up to concentrations of the order of 0.05 and 0.1 mol/kg, re...

A molecular dynamics (MD)-based structural mechanics approach is proposed for the assessment of resilience of buildings. At the core of the approach, potentials of mean force (PMFs) suitable for structural members for both two-body (stretch) and three-body (bending) interactions are derived to define the energy states between mass points discretizi...

Strength and toughness, two important aspects of the durability of concrete structures, are dramatically influenced by the material’s nanotexture, but the question of how the building blocks of cement paste organize themselves to create this nanotexture is still being answered. Recent modelling efforts by CSHub researchers demonstrated a convincing...

Using particle dynamics simulations, we investigate the strength and microstructure of agglomerates of wet frictional particles subjected to axial compression. The numerical model accounts for the cohesive and viscous effects of the binding liquid up to a debonding distance with the liquid assumed to be distributed homogeneously inside the agglomer...

A Grand Canonical Monte Carlo Approach (GCMC) is proposed for the fracture analysis of solids discretized as mass points and bond interactions. In contrast to classical load-driven fracture processes, the GCMC approach introduces an auxiliary field, the bond rupture potential μ to which the system is subjected; in addition to changes in volume V an...

Imagine a household sponge lying next to a kitchen sink. The sponge looks and feels different when it is wet versus when it is dry. When a sponge dries, it shrinks, curls and hardens due to suction forces (called “capillary stress”) which change its mechanical properties. Although the material compositions are different, the same mechanism occurs i...

Between 1993-ˇ2012, more than 75% of catastrophic losses in the United States were caused by windstorms (1). The Congressional Budget Office estimated an average annual damage amounting to $28 billion (0.16 percent of GDP), with a potential rise to $38 billion by 2075 – 55% of which is attributed to coastal development (2). This economic impact of...

Cesium-137 is a common radioactive byproduct found in nuclear spent fuel. Given its 30 year half life, its interactions with potential storage materials—such as cement paste—is of crucial importance. In this paper, simulations are used to establish the interaction of calcium silicate hydrates (C-S-H)—the main binding phase of cement paste—with Cs a...

Structural damping, that is the presence of a velocity dependent dissipative term in the equation of motion, is rationalized as a thermalization process between a structure (here a beam) and an outside bath (understood in a broad sense as a system property). This is achieved via the introduction of the kinetic temperature of structures and formaliz...

We propose a theoretical framework to calculate capillary stresses in complex mesoporous materials, such as moist sand, nanoporous hydrates, and drying colloidal films. Molecular simulations are mapped onto a phase-field model of the liquid-vapor mixture, whose inhomogeneous stress tensor is integrated over Voronoi polyhedra in order to calculate e...

We propose a theoretical framework to calculate capillary stresses in complex mesoporous materials, such as moist sand, nanoporous hydrates, and drying colloidal films. Molecular simulations are mapped onto a phase-field model of the liquid-vapor mixture, whose inhomogeneous stress tensor is integrated over Voronoi polyhedra in order to calculate e...

An urban heat island (UHI) is a climate phenomenon that results in an increased air temperature in cities when compared to their rural surroundings. In this Letter, the dependence of an UHI on urban geometry is studied. Multiyear urban-rural temperature differences and building footprints data combined with a heat radiation scaling model are used t...

2017 was one of the most devastating U.S. hurricane seasons ever recorded. State Departments of Public Safety across the country list tens of thousands of destroyed homes and hundreds of thousands more damaged. Although the total economic impact is still being measured, estimates from NOAA’s National Centers for Environmental Information place dama...

In a context of growing attention for shale gas, the precise impact of organic matter (kerogen) on hydrocarbon recovery from unconventional reservoirs still has to be assessed. Kerogen’s microstructure is characterized by a very disordered pore network that greatly affects hydrocarbon transport. The specific structure and texture of this organic ma...

We report a combined experimental and theoretical study to ascertain carbon solubility in nickel nanoparticles embedded into a carbon matrix via the one-pot method. This original approach is based on the experimental characterization of the magnetic properties of Ni at room temperature and Monte Carlo simulations used to calculate the magnetization...

Molecular structures of kerogen control hydrocarbon production in unconventional reservoirs. Significant progress has been made in developing model representations of various kerogen structures. These models have been widely used for the prediction of gas adsorption and migration in shale matrix. However, using density functional perturbation theor...

The poromechanics of heterogeneous media is reformulated in a discrete framework using the lattice element method (LEM) that accounts for the presence of interfaces as well as local microtextural and elastic variations. The exchange of mechanical information between pore and solid(s) is captured by means of force field potentials for these domains,...

Volume changes in chemically reactive materials, such as hydrating cement, play a critical role in many engineering applications that require precise estimates of stress and pressure developments. But a means to determine bulk volume changes in the absence of other deformation mechanisms related to thermal, pressure and load variations, is still mi...