@article {532, title = {Phase separation of stable colloidal clusters}, journal = {Physical Review Materials}, volume = {2}, year = {2018}, month = {Sep-25-2018}, abstract = {

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 attraction, form system-spanning, out-of-equilibrium networks with glasslike, quasistatic structural relaxation. For reactive systems, we incorporate the free energy landscape of stable prenucleation clusters into the Allen-Cahn reaction equation. We show that pattern formation is dominantly controlled by the Damk\öhler number and the stability of the clusters, which modifies the autocatalytic rate of precipitation. As clusters individually become more stable, bulk phase separation is suppressed.

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}, doi = {10.1103/PhysRevMaterials.2.095602}, url = {https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.2.095602}, author = {Petersen, Thomas and Bazant, Martin Z. and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {570, title = {Poroelasticity of Methane-Loaded Mature and Immature Kerogen from Molecular Simulations}, journal = {Langmuir}, volume = {34}, year = {2018}, month = {Nov-13-2018}, pages = {13766 - 13780}, abstract = {

While 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 so far been performed under the rigid matrix approximation, implying that the pore space is independent of pressure, temperature, and fluid loading, or in other words, neglecting poromechanics. Here, using two hydrogenated porous carbon models as proxies for immature and overmature kerogen, that is, highly aliphatic hydrogen-rich vs highly aromatic hydrogen-poor models, we perform an extensive molecular-dynamics-based investigation of the evolution of the poroelastic properties of those matrices with respect to temperature, external pressure, and methane loading as a prototype alkane molecule. The rigid matrix approximation is shown to hold reasonably well for overmature kerogen even though accounting for flexibility has allowed us to observe the well-known small volume contraction at low fluid loading and temperature. Our results demonstrate that immature kerogen is highly deformable. Within the ranges of conditions considered in this work, its density can double and its accessible porosity (to a methane molecule) can increase from 0 to \∼30\%. We also show that these deformations are significantly nonaffine (i.e., nonhomogeneous), especially upon fluid adsorption or desorption.

}, keywords = {ADSORPTION-INDUCED DEFORMATION; ORGANIC-MATTER; COMPETITIVE ADSORPTION; NANOPOROUS MEDIA; POROUS CARBONS; GLASSY-CARBON; COAL; TRANSPORT; SORPTION; MODEL}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.8b02534}, url = {http://pubs.acs.org/doi/10.1021/acs.langmuir.8b02534}, author = {Obliger, Ama{\"e}l and Valdenaire, Pierre-Louis and Capit, Nicolas and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Jean-Marc Leyssale} } @article {572, title = {Potential-of-Mean-Force Approach for Molecular Dynamics{\textendash}Based Resilience Assessment of Structures}, journal = {Journal of Engineering Mechanics}, volume = {144}, year = {2018}, month = {Aug-2018}, pages = {04018066}, abstract = {

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 discretizing structural members. An original potential parameter calibration procedure is proposed: for close-to-equilibrium potential parameters, the procedure is based on matching measured frequency of a structure with the frequency of the molecular model. In turn, for bond-rupture parameters, it is shown that classical interatomic potential expressions, such as Morse potential, can be used to calibrate the energy content of many structural members and connections. By way of example, the MD-based structural mechanics approach is applied to a large-scale structure. Compared with classical continuum-based approaches, the added value of the method thus proposed is a rational means of determining the progressive structural collapse load of structures based on thermodynamic integration. By redefining structural mechanics within the context of statistical physics, molecular simulations, and potentials of mean force, the approach provides a powerful means of determining fragility curves required for the assessment of resilience of buildings.

}, keywords = {Molecular dynamics; Structural mechanics; Potential of mean force; Morse potential; Progressive structural collapse; Fragility curves}, issn = {0733-9399}, doi = {10.1061/(ASCE)EM.1943-7889.0001491}, url = {http://ascelibrary.org/doi/10.1061/\%28ASCE\%29EM.1943-7889.0001491}, author = {Keremides, Konstantinos and Abdolhosseini Qomi, Mohammad Javad and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {622, title = {The Potential of Mean Force concept for bridging (length and time) scales in the modeling of complex porous materials}, journal = {EPJ Web of Conferences}, volume = {140}, year = {2017}, month = {Jun-30-2017}, pages = {Article Number 01009}, abstract = {

We introduce the concept of Potential of Mean Force, PMF, as a way to implement upscaling modeling from the nano-scale to micron-scale. A PMF is a free energy function representing in an effective way the interactions between objects (cement hydrates, clay platelets, etc.) at thermodynamics conditions. The PMF is therefore the key piece of information allowing to coarse-grained Physical-Chemistry information in a meso-scale model formulation. The use of PMF offers a huge computational advantage as it allows a straight up-scaling to the meso-scale while keeping essential interactions information that are the hallmark of Physical-Chemistry processes. Such a coarse-grained modeling integrates atomistic response into inter-particle potentials that fully propagate molecular scale information all the way to the meso-scale.

}, doi = {10.1051/epjconf/201714001009}, url = {http://www.epj-conferences.org/10.1051/epjconf/201714001009}, author = {Katerina Ioannidou and Benoit Carrier and Matthieu Vandamme and Roland Jean-Marc Pellenq}, editor = {Farhang Radja{\"\i} and Saeid Nezamabadi and Luding, S. and Jean-Yves Delenne} } @article {242, title = {A potential-of-mean-force approach for fracture mechanics of heterogeneous materials using the lattice element method}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {105}, year = {2017}, month = {Aug-2017}, pages = {116 - 130}, abstract = {

Fracture of heterogeneous materials has emerged as a critical issue in many engineering applications, ranging from subsurface energy to biomedical applications, and requires a rational framework that allows linking local fracture processes with global fracture descriptors such as the energy release rate, fracture energy and fracture toughness. This is achieved here by means of a local and a global potential-of-mean-force (PMF) inspired Lattice Element Method (LEM) approach. In the local approach, fracture-strength criteria derived from the effective interaction potentials between mass points are shown to exhibit a scaling commensurable with the energy dissipation of fracture processes. In the global PMF-approach, fracture is considered as a sequence of equilibrium states associated with minimum potential energy states analogous to Griffith\’s approach. It is found that this global approach has much in common with a Grand Canonical Monte Carlo (GCMC) approach, in which mass points are randomly removed following a maximum dissipation criterion until the energy release rate reaches the fracture energy. The duality of the two approaches is illustrated through the application of the PMF-inspired LEM for fracture propagation in a homogeneous linear elastic solid using different means of evaluating the energy release rate. Finally, by application of the method to a textbook example of fracture propagation in a heterogeneous material, it is shown that the proposed PMF-inspired LEM approach captures some well-known toughening mechanisms related to fracture energy contrast, elasticity contrast and crack deflection in the considered two-phase layered composite material.

}, issn = {00225096}, doi = {10.1016/j.jmps.2017.05.006}, author = {Hadrien Laubie and Farhang Radja{\"\i} and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {590, title = {Production of H 2 by water radiolysis in cement paste under electron irradiation: A joint experimental and theoretical study}, journal = {Cement and Concrete Research}, volume = {100}, year = {2017}, month = {Oct-2017}, pages = {110 - 118}, abstract = {

Long-term confinement of nuclear waste is one of the main challenges faced by the nuclear industry. Fission products such as Sr-90 and Cs-137, both beta(-) emitters known to induce serious health hazards, represent the largest fraction of nuclear waste. Cement is a good candidate to store them, provided it can resist the effects of irradiation over time. Here, we have investigated the effects of beta(-) decay on cement by performing electron irradiation experiments on different samples. We show that H-2 production in cement, the main effect of water radiolysis, depends strongly on composition and relative humidity. First-principles calculations indicate that the water-rich interlayer regions with Ca2+ ions act as electron traps that promote the formation of H-2. They also show that holes localize in water-rich regions in low Ca content samples and are then able to participate in H-2 production. This work provides new understanding of radiolysis effects in cements.

}, issn = {00088846}, doi = {10.1016/j.cemconres.2017.05.022}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0008884617302065}, author = {Le Caer, Sophie and Dezerald, Lucile and Boukari, Khaoula and Laine, Maxime and Taupin, s{\'e}bastien and Kavanagh, Ryan M. and Johnston, Conrad S.N. and Foy, Eddy and Charpentier, Thibault and Konrad J. Krakowiak and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Tribello, Gareth A. and Kohanoff, Jorge J. and Andres Sa{\`u}l} } @article {138, title = {Physical Origins of Thermal Properties of Cement Paste}, journal = {Physical Review Applied}, volume = {3}, year = {2015}, month = {Jun-17-2015}, pages = {Article Number: 064010}, abstract = {

Despite the ever-increasing interest in multiscale porous materials, the chemophysical origin of their thermal properties at the nanoscale and its connection to the macroscale properties still remain rather obscure. In this paper, we link the atomic- and macroscopic-level thermal properties by combining tools of statistical physics and mean-field homogenization theory. We begin with analyzing the vibrational density of states of several calcium-silicate materials in the cement paste. Unlike crystalline phases, we indicate that calcium silicate hydrates (CSH) exhibit extra vibrational states at low frequencies (\<2\ \ THz) compared to the vibrational states predicted by the Debye model. This anomaly is commonly referred to as the boson peak in glass physics. In addition, the specific-heat capacity of CSH in both dry and saturated states scales linearly with the calcium-to-silicon ratio. We show that the nanoscale-confining environment of CSH decreases the apparent heat capacity of water by a factor of 4. Furthermore, full thermal conductivity tensors for all phases are calculated via the Green-Kubo formalism. We estimate the mean free path of phonons in calcium silicates to be on the order of interatomic bonds. This satisfies the scale separability condition and justifies the use of mean-field homogenization theories for upscaling purposes. Upscaling schemes yield a good estimate of the macroscopic specific-heat capacity and thermal conductivity of cement paste during the hydration process, independent of fitting parameters.

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}, doi = {10.1103/PhysRevApplied.3.064010}, author = {Mohammad Javad Abdolhosseini Qomi and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @proceedings {100, title = {Poro-chemo-fracture-mechanics ... bottom-up: Application to risk of fracture design of oil and gas cement sheath at early ages}, journal = {Euro-C Conference}, volume = {COMPUTATIONAL MODELLING OF CONCRETE STRUCTURES, VOL 1 }, year = {2014}, month = {Jan-2014}, pages = {61-67}, publisher = {CRC PRESS-TAYLOR \& FRANCIS GROUP}, address = {MAR 24-27, 2014, St Anton am Alberg, AUSTRIA}, abstract = {

With ever more challenging (T, p) environments for cementing applications in oil and gas wells, there is a need to change the classical paradigm of constitutive modeling of the early-age behavior of cementitious materials in oil-and gas well applications. Herein, we propose a bottom-up approach, which starts at the molecular scale of calcium-silicate-hydrates (C-S-H), and propagates this understanding via incremental poroelastic upscaling methods to the meso-and macroscale, and ultimately to the scale of engineering applications. With a clear focus on engineering risk-of-fracture evaluations, we show how to integrate this bottom-up approach with fracture mechanics.

}, isbn = {978-1-138-02641-4; 978-1-315-76203-6}, doi = {10.1201/b16645-8}, author = {Franz-Josef Ulm and Muhannad Abuhaikal and Thomas Alexander Petersen and Roland Jean-Marc Pellenq}, editor = {Bicanic, N and Mang, H and Meschke, G and DeBorst, R} } @article {56, title = {Poromechanics of microporous media}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {60}, year = {2012}, month = {Apr-2012}, pages = {606{\textendash}622}, abstract = {

Microporous media, i.e., porous media made of pores with a nanometer size, are important for a variety of applications, for instance for sequestration of carbon dioxide in coal, or for storage of hydrogen in metal-organic frameworks. In a pore of nanometer size, fluid molecules are not in their bulk state anymore since they interact with the atoms of the solid: they are said to be in an adsorbed state. For such microporous media, conventional poromechanics breaks down.

In this work we derive poroelastic constitutive equations which are valid for a generic porous medium, i.e., even for a porous medium with pores of nanometer size. The complete determination of the poromechanical behavior of a microporous medium requires knowing how the amount of fluid adsorbed depends on both the fluid bulk pressure and the strain of the medium. The derived constitutive equations are validated with the help of molecular simulations on one-dimensional microporous media. Even when a microporous medium behaves linearly in the absence of any fluid (i.e., its bulk modulus does not depend on strain), we show that fluid adsorption can induce non-linear behavior (i.e., its drained bulk modulus can then depend significantly on strain). We also show that adsorption can lead to an apparent Biot coefficient of the microporous medium greater than unity or smaller than zero.

The poromechanical response of a microporous medium to adsorption significantly depends on the pore size distribution. Indeed, the commensurability (i.e., the ratio of the size of the pores to that of the fluid molecules) proves to play a major role. For a one-dimensional model of micropores with a variety of pore sizes, molecular simulations show that the amount of adsorbed fluid depends linearly on the strain of the medium. We derive linearized constitutive equations which are valid when such a linear dependence of the adsorbed amount of fluid on the strain is observed.

As an application, the case of methane and coal is considered. Molecular simulations of an adsorption of methane on a microporous realistic model for coal are performed with a flexible solid skeleton. The applicability of the set of linearized constitutive equations to this case is discussed and the results are shown to be consistent with swelling data measured during a classical adsorption experiment.

Example of molecular configuration. The fluid molecules can enter or leave the ...

Amount of fluid molecules adsorbed per unit length of the undeformed chain, in ...

Apparent tangent drained bulk modulus Kt of the crystalline chain.

}, doi = {10.1016/j.jmps.2012.01.001}, author = {Brochard, Laurent and Matthieu Vandamme and Roland Jean-Marc Pellenq} }