@article {673, title = {Bitumen@SiO2 core-shell particles green synthesis towards flowable powdered bitumen and their binder applications}, journal = {Colloids and Surfaces A: Physicochemical and Engineering Aspects}, volume = {570}, year = {2019}, month = {Mars-20-2019}, pages = {531 - 543}, abstract = {

Mineralization of occulated bitumen emulsions allows producing bitumen powders, also referred to as Bitumen@SiO2 hybrid particles, that can resist storage in hard conditions, with a load up to 8 kPa at 50 \°C during 20 h, without alteration of their morphology or release of their bitumen core. Thanks to the occulation, nal Bitumen@SiO2 powders are not highly pulverulent and allow transportation and handling of bitumen at ambient temperature without the need of water as it is the case for bitumen emulsions. This \“water free\” storage par- ticularity exhibits the double advantage of reducing the cost of transport and of avoiding inhibition of bitumen adhesion at mineral aggregates through the presence of water, therefore rendering the bitumen its high quality of binder. The silica shell is responsible for the high storage stability and, when mixed with aggregates for end use of asphalt, as for example in pavement applications, serves as mineral charge to the bitumen, modifying the bitumen ow properties. Indeed, when heated at 100 \°C and crushed, the capsules break releasing thus the bitumen. This suspension made of bitumen and silica shell fragments exhibits an interesting shear-thinning behavior that can be attributed to the presence of the remnant fragments. Indeed, when shell fragments have been transferred into a silicon oil, initially exhibiting a Newtonian behavior, the mixture of fragments and oil also exhibited a shear thinning rheogram demonstrating the e ect of the silica shell fragments. The bene t of such a behavior modi cation is the possibility to reduce or avoid the usual addition of llers. Passive adhesion has been tested by generating asphalt concretes with Bitumen@SiO2 powders and showed high stability.

}, issn = {09277757}, doi = {10.1016/j.colsurfa.2019.03.048}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0927775719302420}, author = {Anaclet, Pauline and Depardieu, Martin and Laurichesse, Eric and Julien, Viviane and Hung, Yvong and Schmitt, Veronique and Backov, Renal} } @article {665, title = {Cutting floating single-walled carbon nanotubes with a {\textquoteleft}CO2 blade{\textquoteright}}, journal = {Carbon}, volume = {143}, year = {2019}, month = {Mar-2019}, pages = {481 - 486}, abstract = {

Uniform ultra-short (\< 100 nm) single-walled carbon nanotubes (SWCNTs) with properties of rich chemistry, high dispersity and easy manipulation, are of great importance for constructing novel nanostructures and highly integrated miniature devices. Herein, we report a recent breakthrough in cutting long SWCNTs into uniform ultra-short segments in gas-phase using CO2 as a \&$\#$39;blade.\&$\#$39; SWCNTs synthesized by an aerosol reactor are directly introduced into a second reactor for gaseous cutting. The quality and the number concentration of shortened SWCNTs are enhanced after the gas-phase cutting process. Moreover, the growth and cutting of SWCNTs are accomplished in a continuous gas-phase process, thus allows direct dry deposition of ultra-short SWCNTs as individual macromolecules or thin films onto various substrates for multiple applications. (C) 2018 Elsevier Ltd. All rights reserved.

}, issn = {00086223}, doi = {10.1016/j.carbon.2018.11.035}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0008622318310558}, author = {Tian, Ying and Wei, Nan and Laiho, Patrik and Ahmad, Saeed and Yann Magnin and Liao, Yongping and Christophe Bichara and Jiang, Hua and Kauppinen, Esko I.} } @article {594, title = {Investigation of mixed ionic/nonionic building blocks for the dual templating of macro-mesoporous silica}, journal = {Journal of Colloid and Interface Science}, volume = {533}, year = {2019}, month = {Jan-01-2019}, pages = {385 - 400}, abstract = {

Traditional porous monoliths Si(HIPE) (High Internal Phase Emulsion), prepared from the Tetradecyltrimethylammonium Bromide (TTAB)/dodecane/water system, offer high specific surface area, mainly due to microporosity. Aside, mesoporous materials SBA-15, prepared from Pluronic P123, have a high specific surface area, but are obtained as powder, which limits their applications. Starting from the mixed TTAB-P123 surfactant, it is expected to tune the mesoporosity of Si(HIPE), while keeping their monolithic character.

The ternary TTAB/P123/water phase diagram was established by varying the weight ratio between these two surfactants. The micellar structure as well as the structural parameters of the liquid crystal domains were determined by SAXS (Small Angle X-ray Scattering). The effect of dodecane solubilization was also investigated and concentrated emulsions were formulated from the (P123/TTAB)/dodecane/ water systems. After this soft matter dedicated study, the acquired knowledge was transferred toward the hierarchical porous silica generations, where the sol-gel process is involved.

Mixing P123 with TTAB, macro-mesoporous monolithic silica with an enhanced contribution of the specific surface area due to mesoporosity can be prepared. The variation of the TTAB/P123 weight ratio allows controlling the porosity at the mesoscale. Moreover, the macroporosity can be tuned by changing the preparation method, by mixing either the two micellar solutions or directly the two surfactants prior the emulsification process. (C) 2018 Elsevier Inc. All rights reserved.

}, issn = {00219797}, doi = {10.1016/j.jcis.2018.08.068}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0021979718309883}, author = {Roucher, Armand and Emo, Melanie and Vibert, Francois and Stebe, Marie-Jose and Schmitt, Veronique and Jonas, Florian and Backov, Renal and Blin, Jean-Luc} } @article {246, title = {Molecular Modeling and Adsorption Properties of Ordered Silica-Templated CMK Mesoporous Carbons}, journal = {Langmuir}, volume = {33}, year = {2017}, month = {Feb-06-2017}, pages = {2109 - 2121}, abstract = {

Realistic molecular models of silica-templated CMK-1, CMK-3, and CMK-5 carbon materials have been developed by using carbon rods and carbon pipes that were obtained by adsorbing carbon in a model MCM-41 pore. The interactions between the carbon atoms with the silica matrix were described using the PN-Traz potential, and the interaction between the carbon atoms was calculated by the reactive empirical bond order (REBO) potential. Carbon rods and pipes with different thicknesses were obtained by changing the silica\–carbon interaction strength, the temperature, and the chemical potential of carbon vapor adsorption. These equilibrium structures were further used to obtain the atomic models of CMK-1, CMK-3, and CMK-5 materials using the same symmetry as found in TEM pictures. These models are further refined and made more realistic by adding interconnections between the carbon rods and carbon pipes. We calculated the geometric pore size distribution of the different models of CMK-5 and found that the presence of interconnections results in some new features in the pore size distribution. Argon adsorption properties were investigated using GCMC simulations to characterize these materials at 77 K. We found that the presence of interconnection results greatly improves the agreement with available experimental data by shifting the capillary condensation to lower pressures. Adding interconnections also induces smoother adsorption/condensation isotherms, and desorption/evaporation curves show a sharp jump. These features reflex the complexity of the nanovoids in CMKs in terms of their pore morphology and topology.

Abstract Image

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.6b04169}, author = {Jain, Surendra Kumar and Roland Jean-Marc Pellenq and Keith E. Gubbins and Peng, Xuan} } @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 {619, title = {Spectroscopic probe of the van der Waals interaction between polar molecules and a curved surface}, journal = {Physical Review A}, volume = {94}, year = {2016}, month = {Aug-17-2016}, abstract = {

We study the shift of rotational levels of a diatomic polar molecule due to its van der Waals interaction with a gently curved dielectric surface at temperature T, and submicron separations. The molecule is assumed to be in its electronic and vibrational ground state, and the rotational degrees are described by a rigid rotor model. We show that under these conditions retardation effects and surface dispersion can be neglected. The level shifts are found to be independent of T, and given by the quantum state averaged classical electrostatic interaction of the dipole with its image on the surface. We use a derivative expansion for the static Green\&$\#$39;s function to express the shifts in terms of surface curvature. We argue that the curvature induced line splitting is experimentally observable, and not obscured by natural linewidths and thermal broadening.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.94.022509}, url = {https://link.aps.org/doi/10.1103/PhysRevA.94.022509}, author = {Bimonte, Giuseppe and Emig, Thorsten and Jaffe, R. L. and Kardar, Mehran} } @article {179, title = {Advances in design and modeling of porous materials}, journal = {The European Physical Journal Special Topics}, volume = {224}, year = {2015}, month = {Jul-2015}, pages = {1653 - 1653}, abstract = {

This special issue of the European Physical Journal Special Topics is dedicated to selected papers from the symposium \“High surface area porous and granular materials\” organized in the frame of the conference \“Mat\ériaux 2014\”, held on November 24\–28, 2014 in Montpellier, France.

Porous materials and granular materials gather a wide variety of heterogeneous, isotropic or anisotropic media made of inorganic, organic or hybrid solid skeletons, with open or closed porosity, and pore sizes ranging from the centimeter scale to the sub-nanometer scale. Their technological and industrial applications cover numerous areas from building and civil engineering to microelectronics, including also metallurgy, chemistry, health, waste water and gas effluent treatment. Many emerging processes related to environmental protection and sustainable development also rely on this class of materials. Their functional properties are related to specific transfer mechanisms (matter, heat, radiation, electrical charge), to pore surface chemistry (exchange, adsorption, heterogeneous catalysis) and to retention inside confined volumes (storage, separation, exchange, controlled release). The development of innovative synthesis, shaping, characterization and modeling approaches enables the design of advanced materials with enhanced functional performance. The papers collected in this special issue offer a good overview of the state-of-the-art and science of these complex media.

We would like to thank all the speakers and participants for their contribution to the success of the symposium. We also express our gratitude to the organization committee of \“Mat\´eriaux 2014\”. We finally thank the reviewers and the staff of the European Physical Journal Special Topics who made the publication of this special issue possible.

}, issn = {1951-6355}, doi = {10.1140/epjst/e2015-02487-6}, author = {Ayral, Andre and Calas-Etienne, Sylvie and Benoit A. Coasne and Deratani, Andr{\'e} and Evstratov, Alexis and Anne Galarneau and Grande, Daniel and Hureau, Matthieu and Jobic, Herv{\'e} and Morlay, Catherine and Parmentier, Julien and Prelot, B{\'e}n{\'e}dicte and Rossignol, Sylvie and Simon-Masseron, Ang{\'e}lique and Thibault-Starzyk, Fr{\'e}d{\'e}ric} } @article {176, title = {Control of the Pore Texture in Nanoporous Silicon via Chemical Dissolution}, journal = {Langmuir}, volume = {31}, year = {2015}, month = {Jul-28-2015}, pages = {8121 - 8128}, abstract = {
Abstract Image

The surface and textural properties of porous silicon (pSi) control many of its physical properties essential to its performance in key applications such as optoelectronics, energy storage, luminescence, sensing, and drug delivery. Here, we combine experimental and theoretical tools to demonstrate that the surface roughness at the nanometer scale of pSi can be tuned in a controlled fashion using partial thermal oxidation followed by removal of the resulting silicon oxide layer with hydrofluoric acid (HF) solution. Such a process is shown to smooth the pSi surface by means of nitrogen adsorption, electron microscopy, and small-angle X-ray and neutron scattering. Statistical mechanics Monte Carlo simulations, which are consistent with the experimental data, support the interpretation that the pore surface is initially rough and that the oxidation/oxide removal procedure diminishes the surface roughness while increasing the pore diameter. As a specific example considered in this work, the initial roughness \ξ \∼ 3.2 nm of pSi pores having a diameter of 7.6 nm can be decreased to 1.0 nm following the simple procedure above. This study allows envisioning the design of pSi samples with optimal surface properties toward a specific process.

}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.5b01518}, author = {Secret, Emilie and Wu, Chia-Chen and Chaix, Arnaud and Anne Galarneau and Gonzalez, Philippe and Cot, Didier and Sailor, Michael J. and Jestin, Jacques and Zanotti, Jean-Marc and Cunin, Fr{\'e}d{\'e}rique and Benoit A. Coasne} } @article {151, title = {Inference of the phase-to-mechanical property link via coupled X-ray spectrometry and indentation analysis: Application to cement-based materials}, journal = {Cement and Concrete Research}, volume = {67}, year = {2015}, month = {Jan-2015}, pages = {271 - 285}, abstract = {

A novel approach for the chemo-mechanical characterization of cement-based materials is presented, which combines the classical grid indentation technique with elemental mapping by scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS). It is illustrated through application to an oil-well cement system with siliceous filler. The characteristic X-rays of major elements (silicon, calcium and aluminum) are measured over the indentation region and mapped back on the indentation points. Measured intensities together with indentation hardness and modulus are considered in a clustering analysis within the framework of Finite Mixture Models with Gaussian component density function. The method is able to successfully isolate the calcium-silica-hydrate gel at the indentation scale from its mixtures with other products of cement hydration and anhydrous phases; thus providing a convenient means to link mechanical response to the calcium-to-silicon ratio quantified independently via X-ray wavelength dispersive spectroscopy. A discussion of uncertainty quantification of the estimated chemo-mechanical properties and phase volume fractions, as well as the effect of chemical observables on phase assessment is also included.

}, issn = {00088846}, doi = {10.1016/j.cemconres.2014.09.001}, author = {Konrad J. Krakowiak and Wilson, William and James, Simon and Musso, Simone and Franz-Josef Ulm} } @article {645, title = {Magnetic nanopantograph in the SrCu 2 (BO 3 ) 2 Shastry{\textendash}Sutherland lattice}, journal = {Proceedings of the National Academy of Sciences}, volume = {112}, year = {2015}, month = {Feb-17-2015}, pages = { 1971-1976}, abstract = {

Magnetic materials having competing, i.e., frustrated, interactions can display magnetism prolific in intricate structures, discrete jumps, plateaus, and exotic spin states with increasing applied magnetic fields. When the associated elastic energy cost is not too expensive, this high potential can be enhanced by the existence of an omnipresent magnetoelastic coupling. Here we report experimental and theoretical evidence of a nonnegligible magnetoelastic coupling in one of these fascinating materials, SrCu2(BO3)(2) (SCBO). First, using pulsed-field transversal and longitudinal magnetostriction measurements we show that its physical dimensions, indeed, mimic closely its unusually rich field-induced magnetism. Second, using density functional-based calculations we find that the driving force behind the magnetoelastic coupling is the CuOCu superexchange angle that, due to the orthogonal Cu2+ dimers acting as pantographs, can shrink significantly (0.44\%) with minute (0.01\%) variations in the lattice parameters. With this original approach we also find a reduction of similar to 10\% in the intradimer exchange integral J, enough to make predictions for the highly magnetized states and the effects of applied pressure on SCBO.

}, issn = {0027-8424}, doi = {10.1073/pnas.1421414112}, url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1421414112}, author = {Guillaume Radtke and Andres Sa{\`u}l and Dabkowska, Hanna A. and Salamon, Myron B. and Jaime, Marcelo} } @article {117, title = {Magnetic nanopantograph in the SrCu2(BO3)2 Shastry{\textendash}Sutherland lattice}, journal = {Proceedings of the National Academy of Sciences}, volume = {112}, year = {2015}, month = {Feb-02-2015}, pages = {1971-1976}, abstract = {

Magnetic materials having competing, i.e., frustrated, interactions can display magnetism prolific in intricate structures, discrete jumps, plateaus, and exotic spin states with increasing applied magnetic fields. When the associated elastic energy cost is not too expensive, this high potential can be enhanced by the existence of an omnipresent magnetoelastic coupling. Here we report experimental and theoretical evidence of a nonnegligible magnetoelastic coupling in one of these fascinating materials, SrCu2(BO3)2 (SCBO). First, using pulsed-field transversal and longitudinal magnetostriction measurements we show that its physical dimensions, indeed, mimic closely its unusually rich field-induced magnetism. Second, using density functional-based calculations we find that the driving force behind the magnetoelastic coupling is the CuOCu^ superexchange angle that, due to the orthogonal Cu2+ dimers acting as pantographs, can shrink significantly (0.44\%) with minute (0.01\%) variations in the lattice parameters. With this original approach we also find a reduction of \∼10\% in the intradimer exchange integral J, enough to make predictions for the highly magnetized states and the effects of applied pressure on SCBO.

}, doi = {10.1073/pnas.1421414112}, author = {Guillaume Radtke and Andres Sa{\`u}l and Dabkowska, Hanna A. and Salamon, Myron B. and Jaime, Marcelo} } @article {150, title = {Nano-chemo-mechanical signature of conventional oil-well cement systems: Effects of elevated temperature and curing time}, journal = {Cement and Concrete Research}, volume = {67}, year = {2015}, month = {Jan-2015}, pages = {103 - 121}, abstract = {

With ever more challenging (T,p) environments for cementing applications in oil and gas wells, there is a need to identify the fundamental mechanisms of fracture resistant oil well cements. We report results from a multi-technique investigation of behavior and properties of API class G cement and silica-enriched cement systems subjected to hydrothermal curing from 30\ \°C to 200\ \°C; including electron probe microanalysis, X-ray diffraction, thermogravimetry analysis, electron microscopy, neutron scattering (SANS), and fracture scratch testing. The results provide a new insight into the link between system chemistry, micro-texture and micro-fracture toughness. We suggest that the strong correlation found between chemically modulated specific surface and fracture resistance can explain the drop in fracture properties of neat oil-well cements at elevated temperatures; the fracture property enhancement in silica-rich cement systems, between 110\° and 175\ \°C; and the drop in fracture properties of such systems through prolonged curing over 1\ year at 200\ \°C.

Fig.1. Particle size distribution of the silica flour (ground quartz) incorporated{\textellipsis}

Fig.2. Location of the {\textquotedblleft}chemical poles{\textquotedblright} of the cement clinker and cement hydration{\textellipsis}

Fig.3. Simplified schematic of: (a) the cement paste microstructure cured at room{\textellipsis}

Fig.4. A schematic of the effect of adding an extra dimension, Al, to the statistical{\textellipsis}

Fig.5. X-ray powder diffraction spectra with qualitative analysis of the major phases{\textellipsis}

Fig.6. Thermal gravimetric analysis (TGA) carried out on samples cured in the{\textellipsis}

}, issn = {00088846}, doi = {10.1016/j.cemconres.2014.08.008}, author = {Konrad J. Krakowiak and Jeffrey J. Thomas and Musso, Simone and James, Simon and Ange-Therese Akono and Franz-Josef Ulm} } @article {625, title = {Native Morphology of Hydrated Spheroidal Halloysite Observed by Environmental Transmission Electron Microscopy}, journal = {Clays and Clay Minerals}, volume = {63}, year = {2015}, month = {Oct-2015}, pages = {368 - 377}, abstract = {

Natural mineral materials such as tabular and spheroidal halloysites have recently been suggested as candidates for intercalating metal ions or organic molecules. Their potential use as nano-adsorbents is related to their porous structure and water content. Although the two morphologies can coexist in natural deposits, spheroidal halloysites remain poorly characterized whereas much literature exists on tubular halloysites. The present study investigates the native morphology, internal porous structure, and behavior upon dehydration of spheroidal halloysite from Opotiki (New Zealand). This mineral was characterized in its natural hydrated state using a transmission electron microscope equipped with an environmental cell (EC-TEM). The sample was placed in a sealed block in which water vapor-saturated air circulated at a pressure of 30 Torr. The observed particles consisted of almost complete spheroids displaying polyhedral external surfaces. 1:1 layers stack concentrically as a pore-free, onion-like structure. The dynamic processes of dehydration created by slow depressurization of the cell resulted in a decrease in the layer-to-layer distance (d001) from ~10 \Å to ~7 \Å due to the loss of interlayer water molecules. Irreversible formation of spurious \‘internal pores\’ was recorded during this process. These pores were not indigenous to the hydrated 10 \Å halloysite and resulted from the collapse of the native layers. They cannot account for the physical chemical properties of spheroidal halloysite. Spheroidal halloysites would have a lower propensity for intercalating ions or molecules than tubular halloysites. Isolated facets were also observed in high-resolution-TEM and displayed a pseudo-hexagonal morphology. The three-dimensional microstructure of the spheroid appeared bent along the three pseudo equivalent yi directions of the kaolinite-like single layers. An analogy with polyhedral serpentine has allowed the proposal of a formation process of hydrated spheroidal halloysite triggered by enrichment in divalent ions in the growth system.

}, issn = {00098604}, doi = {10.1346/CCMN.2015.0630503}, url = {http://openurl.ingenta.com/content/xref?genre=article\&issn=0009-8604\&volume=63\&issue=5\&spage=368}, author = {Berthonneau, Jeremie and Grauby, Olivier and Jeannin, Charlotte and Chaudanson, Damien and Joussein, Emmanuel and Alain Baronnet} } @article {39, title = {An atomistic modeling of the xenon bubble behavior in the UO2 matrix}, journal = {Journal of Nuclear Materials}, volume = {444}, year = {2014}, month = {Jan-2014}, pages = {153{\textendash}160}, abstract = {

The behavior of the xenon nanoinclusions/bubbles in the uranium dioxide (UO2) matrix and their influence on its swelling were investigated through atomistic simulation techniques. The pressure in bubbles of less than 2\ nm in diameter, calculated using a virial equation that takes into account the xenon/matrix interactions, is larger than the pressure calculated in simulations of the equivalent density and temperature of super critical bulk xenon. The radial distribution function of confined xenon is characteristic of a dense (\ \>\ 4\ g/cm3) glassy phase. The swelling of the UO2 induced by the intragranular bubbles is proportional to the Xe/U ratio but independent of the temperature.

The UO2 elementary cell. It contains 4 uranium atoms (large spheres) forming a ...

Comparison between the density versus pressure ρ(P) curves calculated at 298K ...

Comparison between the bulk modulus versus pressure K(P) curves calculated at ...

}, doi = {10.1016/j.jnucmat.2013.09.041}, author = {Andrei Jelea and Roland Jean-Marc Pellenq and F. Ribeiro} } @article {72, title = {Combinatorial molecular optimization of cement hydrates}, journal = {Nat Commun}, volume = {5}, year = {2014}, month = {Sep-24-2014}, pages = {Article Number: 4960}, abstract = {

Despite its ubiquitous presence in the built environment, concrete\â\€$(1s (Bmolecular-level properties are only recently being explored using experimental and simulation studies. Increasing societal concerns about concrete\â\€$(1s (Benvironmental footprint have provided strong motivation to develop new concrete with greater specific stiffness or strength (for structures with less material). Herein, a combinatorial approach is described to optimize properties of cement hydrates. The method entails screening a computationally generated database of atomic structures of calcium-silicate-hydrate, the binding phase of concrete, against a set of three defect attributes: calcium-to-silicon ratio as compositional index and two correlation distances describing medium-range silicon-oxygen and calcium-oxygen environments. Although structural and mechanical properties correlate well with calcium-to-silicon ratio, the cross-correlation between all three defect attributes reveals an indentation modulus-to-hardness ratio extremum, analogous to identifying optimum network connectivity in glass rheology. We also comment on implications of the present findings for a novel route to optimize the nanoscale mechanical properties of cement hydrate.

Figure 1

}, doi = {10.1038/ncomms5960}, author = {Mohammad Javad Abdolhosseini Qomi and Konrad J. Krakowiak and Mathieu Bauchy and Stewart, K.L. and Rouzbeh Shahsavari and Jagannathan, D. and Brommer, D.B. and Alain Baronnet and Markus J Buehler and Sidney Yip and Franz-Josef Ulm and Krystyn J. Van Vliet and Roland Jean-Marc Pellenq} } @article {89, title = {Effect of Gas Adsorption on Acoustic Wave Propagation in MFI Zeolite Membrane Materials: Experiment and Molecular Simulation}, journal = {Langmuir}, volume = {30}, year = {2014}, month = {Aug-04-2014}, pages = {10336-10343}, type = {Article}, abstract = {
Abstract Image

The present study reports on the development of a characterization method of porous membrane materials which consists of considering their acoustic properties upon gas adsorption. Using acoustic microscopy experiments and atomistic molecular simulations for helium adsorbed in a silicalite-1 zeolite membrane layer, we showed that acoustic wave propagation could be used, in principle, for controlling the membranes operando. Molecular simulations, which were found to fit experimental data, showed that the compressional modulus of the composite system consisting of silicalite-1 with adsorbed He increases linearly with the He adsorbed amount while its shear modulus remains constant in a large range of applied pressures. These results suggest that the longitudinal and Rayleigh wave velocities (VL and VR) depend on the He adsorbed amount whereas the transverse wave velocity VT remains constant.

}, issn = {0743-7463}, doi = {10.1021/la502182k}, author = {Manga, Etoungh D. and Blasco, Hugues and J. Philippe Da-Costa and Drobek, Martin and Ayral, Andre and Le Clezio, Emmanuel and Despaux, Gilles and Benoit A. Coasne and Julbe, Anne} } @proceedings {99, title = {Modelling cement at fundamental scales: From atoms to engineering strength and durability}, journal = {Euro-C Conference}, volume = {COMPUTATIONAL MODELLING OF CONCRETE STRUCTURES, VOL 1}, year = {2014}, month = {2014}, pages = {139-148}, publisher = {CRC Press-Taylor \& Francis Group}, address = {MAR 24-27, 2014, St Anton am Alberg, AUSTRIA}, abstract = {

The mechanics and rheology of cement pastes are largely determined by the Calcium-Silicate-Hydrate (C-S-H) gel, which is normally the main binding phase. The C-S-H gel is an amorphous material with a nanoscale pore network. Here we consider a model structure of the gel, where a continuous molecular model of non-porous C-S-H is combined with a colloidal model that incorporates the porosity of the gel. Numerical simulations predict mechanical properties and microscopic processes associated with yielding under shear. The proposed model can now be used to extract further properties and to contribute to a broader effort aimed at describing and engineering the multi-scale structure and mechanical behaviour of the cement paste. We finally discuss the opportunities offered by our model with respect to the scientific and technological challenges of modelling and controlling ageing and creep over long time scales.

}, isbn = {978-1-138-02641-4; 978-1-315-76203-6}, doi = {10.1201/b16645-16}, author = {Enrico Masoero and Hamlin M. Jennings and Franz-Josef Ulm and Emanuela Del Gado and Hegoi Manzano and Roland Jean-Marc Pellenq and Sidney Yip}, editor = {Bicanic, N and Mang, H and Meschke, G and DeBorst, R} } @article {35, title = {Adsorption of Aromatic Hydrocarbon Molecules at the Surface of Ice, As Seen by Grand Canonical Monte Carlo Simulation}, journal = {The Journal of Physical Chemistry C}, volume = {117}, year = {2013}, month = {Apr-2013}, pages = {6719{\textendash}6729}, abstract = {
Abstract Image

The adsorption of four aromatic hydrocarbon compounds, benzene, naphthalene, anthracene, and phenanthrene, at the surface of Ih ice is investigated by grand canonical Monte Carlo (GCMC) computer simulation under tropospheric conditions at 200 K. By systematic variation of the value of adsorbate chemical potential in the simulations, the adsorption isotherms are determined. It is found that adsorption follows the Langmuir mechanism only up to a rather low relative pressure value in every case. In this range specific surface sites, called \α sites, to which adsorbate molecules can be bound particularly strongly in specific orientation, are occupied. In these \α sites, presumably the dangling OH bonds of the ice surface form O\–H....\π-type hydrogen bonds with the delocalized \π electrons of the adsorbed aromatic molecule lying parallel with the ice surface. Once these \α sites are saturated, lateral interactions become increasingly important, leading to large fluctuations of the lateral density of the adsorption layer and an increasing deviation of the adsorption isotherm from the Langmuir shape. The adsorption layer is found to be strictly monomolecular and even unsaturated in every case, as condensation well precedes the saturation of this monolayer for all four aromatic adsorbates considered in this study.

}, doi = {10.1021/jp401532x}, author = {M{\'e}sz{\'a}r, Zsuzsanna E and Gy{\"o}rgy Hantal and Picaud, Sylvain and Jedlovszky, P{\'a}l} } @proceedings {365, title = {AIP Conference Proceedings A multiscale description of failure in granular materials}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {585-588}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

This paper presents conditions of initiation and development of failure in granular materials through a twodimensional discrete element model. General condition for the effective development of failure and its physical characteristics are recalled. Then relation between failure and the second order work expressed in terms of microscopic variables is discussed. Eventually, correspondence between a localized mode of failure marked with shear band patterns and space distribution of negative values of microscopic second-order work is investigated.

}, doi = {10.1063/1.4811999}, author = {Hadda, Nejib and Fran{\c c}ois Nicot and Sibille, Luc and Farhang Radja{\"\i} and Tordesillas, Antoinette and Darve, F{\'e}lix}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {366, title = {AIP Conference ProceedingsTumbling sandpiles in a fluid}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jul-2013}, pages = {662-665}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

By means of contact dynamics simulations interfaced with computational fluid dynamics, we analyze the effect of a suspending fluid on the dynamics of collapse and spread of a granular column. We find that the runout distance increases as a power law with the aspect ratio of the column and, for a given aspect ratio, it may be the same in the grain-inertial and fluid-inertial regimes but with considerably longer duration in the latter case. We show that, in both viscous and fluid-inertial regimes, this behavior results from compensation between two effects of the fluid: 1) reduction of the kinetic energy during collapse and 2) enhancement of the flow by lubrication during spread.

}, doi = {10.1063/1.4812018}, author = {Farhang Radja{\"\i} and Vincent Topin and Perales, F. and Yann Monerie}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {367, title = {A benchmark for particle shape dependence}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {883-886}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Particle shape is a major parameter for the space-filling and strength properties of granular materials. For a systematic investigation of shape effect, a numerical benchmark test was set up within a collaborative group using different numerical methods and particles of various shape characteristics such as elongation, angularity and nonconvexity. Extensive 2D shear simulations were performed in this framework and the shear strength and packing fraction were compared for different shapes. We show that the results may be analyzed in terms of a low-order shape parameter \η describing the degree of distortion from a perfectly circular shape. In particular, the shear strength is an increasing function of \η with nearly the same trend for all shapes, the differences being of second order compared to \η. We also observe a nontrivial behavior of packing fraction which, for all our simulated shapes, increases with \η from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as \η is further increased. Finally, the analysis of contact forces for the same value of \η leads to very similar statistics regardless of our specific particle shapes.

}, doi = {10.1063/1.4812073}, author = {Gael Combe and C{\'e}cile Nouguier-Lehon and Emilien Az{\'e}ma and Krzysztof Szarf and Baptiste Saint-Cyr and Marie Chaze and Farhang Radja{\"\i} and Pascal Villard and Jean-Yves Delenne and Vincent Richefeu and Philippe Sornay and Charles Voivret and CEGEO Group}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {369, title = {Capillary states of granular materials in the funicular state}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {1023-1026}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Using a multi-phase lattice Boltzmann model, we investigate the capillary states of a 2D granular packing gradually saturated by condensation from a homogeneously injected vapor phase. The internal stresses induced by surface tension and Laplace pressure are directly calculated from the forces acting on the grains with increasing amount of liquid. The evolution of cohesive strength with the amount of liquid reveals four different states reflecting the connectivity of the liquid phase and local grain environments. It increases in the pendular state, characterized by binary liquid bridges holding the grains together, and within the funicular state with an increasing number of liquid clusters connected to several grains. Beyond 40\% of saturation, the cohesive strength falls off due to a decreasing Laplace pressure of liquid clusters.

}, doi = {10.1063/1.4812108}, author = {Jean-Yves Delenne and Vincent Richefeu and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {368, title = {Comparison of the effects of rolling resistance and angularity in sheared granular media}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jul-2013}, pages = {891-894}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

In this paper, we compare the effect of rolling resistance at the contacts in granular systems composed of disks with the effect of angularity in granular systems composed of regular polygonal particles. For this purpose, we use contact dynamics simulations. By means of a simple shear numerical device, we investigate the mechanical behavior of these materials in the steady state in terms of shear strength, solid fraction, force and fabric anisotropies, and probability distribution of contact forces. We find that, based on the energy dissipation associated with relative rotation between two particles in contact, the effect of rolling resistance can explicitly be identified with that of the number of sides in a regular polygonal particle. This finding supports the use of rolling resistance as a shape parameter accounting for particle angularity and shows unambiguously that one of the main influencing factors behind the mechanical behavior of granular systems composed of noncircular particles is the partial hindrance of rotations as a result of angular particle shape.

}, keywords = {angularity, anisotropy, force distribution, Granular material, rolling resistance, Shear strength, solid fraction}, url = {https://hal.archives-ouvertes.fr/hal-00842799}, author = {Estrada, Nicolas and Emilien Az{\'e}ma and Farhang Radja{\"\i} and Taboada, Alfredo}, editor = {Yu, A and Dong, K and Yang, R} } @article {25, title = {Large pressure enhancements in confined phases: effect of surface chemistry and roughness}, journal = {J. Chem. Phys.}, volume = {139}, year = {2013}, month = {Oct-10-2013}, chapter = {144701}, abstract = {

Experiments and simulations both suggest that the pressure experienced by an adsorbed phase confined within a carbon nanoporous material can be several orders of magnitude larger than the bulk phase pressure in equilibrium with the system. To investigate this pressure enhancement, we report a molecular-simulation study of the pressure tensor of argon confined in slit-shaped nanopores with walls of various models, including carbon and silica materials. We show that the pressure is strongly enhanced by confinement, arising from the effect of strongly attractive wall forces; confinement within purely repulsive walls does not lead to such enhanced pressures. Simulations with both the Lennard-Jones and Barker-Fisher-Watts intermolecular potentials for argon-argon interactions give rise to similar results. We also show that an increase in the wall roughness significantly decreases the in-pore pressure due to its influence on the structure of the adsorbate. Finally, we demonstrate that the pressures calculated from the mechanical (direct pressure tensor calculations) and the thermodynamic (volume perturbation method) routes yield almost identical results, suggesting that both methods can be used to calculate the local pressure tensor components in the case of these planar geometries.

Image of FIG. 1.
Image of FIG. 2.
Image of FIG. 3.
Image of FIG. 4.
}, doi = {10.1063/1.4824125}, author = {Yun Long and Jeremy C. Palmer and Benoit A. Coasne and Malgorzata Sliwinska-Bartkowiak and George Jackson and Erich A. Mueller and Keith E. Gubbins} } @article {103, title = {On the molecular origin of high-pressure effects in nanoconfinement: The role of surface chemistry and roughness}, journal = {Journal of Chemical Physics}, volume = {139}, year = {2013}, month = {Oct-14-2013}, type = {Article}, abstract = {

Experiments and simulations both suggest that the pressure experienced by an adsorbed phase confined within a carbon nanoporous material can be several orders of magnitude larger than the bulk phase pressure in equilibrium with the system. To investigate this pressure enhancement, we report a molecular-simulation study of the pressure tensor of argon confined in slit-shaped nanopores with walls of various models, including carbon and silica materials. We show that the pressure is strongly enhanced by confinement, arising from the effect of strongly attractive wall forces; confinement within purely repulsive walls does not lead to such enhanced pressures. Simulations with both the Lennard-Jones and Barker-Fisher-Watts intermolecular potentials for argon-argon interactions give rise to similar results. We also show that an increase in the wall roughness significantly decreases the in-pore pressure due to its influence on the structure of the adsorbate. Finally, we demonstrate that the pressures calculated from the mechanical (direct pressure tensor calculations) and the thermodynamic (volume perturbation method) routes yield almost identical results, suggesting that both methods can be used to calculate the local pressure tensor components in the case of these planar geometries. (C) 2013 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4824125}, author = {Yun Long and Jeremy C. Palmer and Benoit A. Coasne and Malgorzata Sliwinska-Bartkowiak and George Jackson and Erich A. Mueller and Keith E. Gubbins} } @article {30, title = {Nanofluidic Osmotic Diodes: Theory and Molecular Dynamics Simulations}, journal = {Physical Review Letters}, volume = {111}, year = {2013}, month = {Dec-2013}, pages = {244501}, abstract = {

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.

Figure

Figure

Figure

Figure

}, doi = {10.1103/PhysRevLett.111.244501}, author = {Picallo, Clara B and Simon Gravelle and Joly, Laurent and Charlaix, Elisabeth and Lyd{\'e}ric Bocquet} } @article {66, title = {Optimizing water permeability through the hourglass shape of aquaporins}, journal = {Proceedings of the National Academy of Sciences}, volume = {110}, year = {2013}, month = {Oct-08-2013}, pages = {16367{\textendash}16372}, abstract = {

The ubiquitous aquaporin channels are able to conduct water across cell membranes, combining the seemingly antagonist functions of a very high selectivity with a remarkable permeability. Whereas molecular details are obvious keys to perform these tasks, the overall efficiency of transport in such nanopores is also strongly limited by viscous dissipation arising at the connection between the nanoconstriction and the nearby bulk reservoirs. In this contribution, we focus on these so-called entrance effects and specifically examine whether the characteristic hourglass shape of aquaporins may arise from a geometrical optimum for such hydrodynamic dissipation. Using a combination of finite-element calculations and analytical modeling, we show that conical entrances with suitable opening angle can indeed provide a large increase of the overall channel permeability. Moreover, the optimal opening angles that maximize the permeability are found to compare well with the angles measured in a large variety of aquaporins. This suggests that the hourglass shape of aquaporins could be the result of a natural selection process toward optimal hydrodynamic transport. Finally, in a biomimetic perspective, these results provide guidelines to design artificial nanopores with optimal performances.

}, doi = {10.1073/pnas.1306447110}, author = {Simon Gravelle and Joly, Laurent and Detcheverry, Fran{\c c}ois and Christophe Ybert and Cottin-Bizonne, C{\'e}cile and Lyd{\'e}ric Bocquet} } @proceedings {360, title = {Penetration strength of coarse granular materials from DEM simulations}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013 }, year = {2013}, month = {Jun-18-2013}, pages = { 241-244}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer test is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. In fact, the data are considerably more sensitive to various parameters such as fabric structure, particles shape or the applied impact energy. In order to achieve a better understanding of the underlying phenomena, we performed a numerical study by means contact dynamics DEM simulations. We consider the penetration of a moving tip into a sample composed of irregular grain shapes and we analyze the influence of the driving velocity and applied energy on the penetration strength. We find that the latter grows with both the penetration rate and energy. Force fluctuations on the tip involve a jamming-unjamming process. The typology of contact network and inter-granular friction play a major role in the fluctuations and measured values of the cone penetration strength.

}, doi = {10.1063/1.4811912}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {361, title = {Settlement statistics of a granular layer composed of polyhedral particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {333-336}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

We use 3D contact dynamics simulations to investigate the mechanical equilibrium and settlement of a granular material composed of irregular polyhedral particles confined between two horizontal frictional planes. We show that, as a consequence of mobilized wall-particle friction force at the top and bottom boundaries, the transient deformation induced by a constant vertical load increment is controlled by the aspect ratio (thickness over width) of the packing as well as the stress ratio. The transient deformation declines considerably for increasingly smaller aspect ratios and grows with the stress ratio. From the simulation data for a large number of independent configurations, we find that sample-to-sample fluctuations of the deformation have a broad distribution and they scale with the average deformation.

}, doi = {10.1063/1.4811935}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {363, title = {Shear strength and microstructure of 3D assemblies of platy particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jul-09-2013}, pages = {519-522}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

As a first step towards particle-scale modeling of clayey soils, we investigate the mechanical behavior and microstructure of assemblies of three-dimensional rectangular platy particles by means of the discrete element method. Several samples composed of particles of different levels of platyness (ratio of width to thickness) were numerically prepared and sheared to large deformations. We analyze the shear strength, packing fraction, connectivity, contact and force anisotropies, and mobilization of friction forces as functions of platyness.We find that both the mechanical behavior and microstructure are strongly dependent on the degree of platyness. This happens, in particular, because of the alignment of particle faces along a particular direction. Additionally, as observed for other granular materials with complex shapes, the packing fraction passes by a peak value before decreasing for larger values of platyness.

}, keywords = {Clays, DEM, Microstructure, Shear strength}, url = {https://hal.archives-ouvertes.fr/hal-00842787}, author = {Boton, Mauricio and Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i} and Lizcano, Arcesio}, editor = {Yu, A and Dong, K and Yang, R} } @proceedings {362, title = {Shear strength, force distributions and friction mobilization in sheared packings composed of angular particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {2013}, pages = {511-514}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

In this paper, we explore the effect of particle shape angularity on the mechanical behavior of sheared granular packings. A first series of contact dynamics simulations is performed in 2D with regular polygons with an increasing number of sides ranging from 3 (triangles) to 60. Then, in order to approach \“idealized\” angular particles, a second series of simulations is performed in 3D with irregular polyhedra with the number of faces ranging from 8 (octahedron-like) to 596. A counterintuitive finding is that the shear strength increases with angularity up to a maximum value and saturates as the particles become more angular (below 6 sides in 2D and 46 faces in 3D). A micromechanical analysis of force and contact orientations, all enhanced by face-face and face-side contacts, reveals that this increase is due to an increase of both contact and force anisotropies, and the saturation for higher angularities is a consequence of a rapid fall-off of the contact and normal force anisotropies compensated by an increase of the tangential force anisotropy.

}, doi = {10.1063/1.4811980}, author = {Emilien Az{\'e}ma and Estrada, Nicolas and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @conference {36, title = {Water Isotherms, Shrinkage and Creep of Cement Paste: Hypotheses, Models and Experiments}, booktitle = {Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete: A Tribute to Zdenek P. Ba{\.z}ant}, year = {2013}, month = {Sep-25-2013}, publisher = {ASCE Publications}, organization = {ASCE Publications}, abstract = {

Cement paste has a complex mesoscale structure, and small changes in its pore network potentially cause large variation in measurements such as the water isotherm (also nitrogen). We deconvolute the water isotherm with the help of advanced computational techniques, hypotheses, and a re-examination of published data. The pore system is divided into four different categories, each containing water with its own physical properties. By viewing the highly interdependent roles of water in each of the pore categories as a system, new insights are gained regarding possible mechanisms that control drying, shrinkage, and creep, and experimental strategies for verification.

}, doi = {10.1061/9780784413111.015}, author = {Hamlin M. Jennings and Enrico Masoero and Pinson, Matthew B and Strekalova, Elena G and Patrick A Bonnaud and Hegoi Manzano and Qing Ji and Jeffrey J. Thomas and Roland Jean-Marc Pellenq and Franz-Josef Ulm and others} } @article {94, title = {Comparison of computational water models for simulation of calcium-silicate-hydrate}, journal = {Computational Materials Science}, volume = {53}, year = {2012}, month = {Feb-2012}, pages = {234-240}, type = {Article}, abstract = {

Calcium silicate hydrate, or C-S-H, is the chief hydration product of Portland cement. The structure of the C-S-H phase within cement has been proposed and developed via molecular simulations. In such simulations, empirical interatomic potentials for water molecules within C-S-H are adopted to govern the position and relative motion of this key constituent. Initial simulations and force fields of C-S-H have assumed the simplest molecular model of H2O termed {\textquoteleft}{\textquoteleft}single point charge{\&$\#$39;\&$\#$39;} or SPC, but this choice has not been validated by comparison with other computational models of water that confer additional bond flexibility or charge distribution. To enable efficiently computational modeling of C-S-H and to explore the role that H2O plays in maintaining C-S-H structure and properties, the choice of an efficient and accurate water model is critical. Here, we consider five distinct, classical atomistic water models (SPC, TIP3P, TIP4P, TIP4P05, and TIP5P) to determine the effects of these computational simplifications on C-S-H properties. Quantitative comparison of all five water models shows that the appropriate water model depends on the C-S-H characteristics of interest. Among these models, both SPC and TIP5P models successfully predict key properties of the structure and elastic constants of C-S-H, as well as the dynamics of water molecules within C-S-H. (C) 2011 Elsevier B. V. All rights reserved.

Schematics of (a) five water models and (b) calcium{\textendash}silicate{\textendash}hydrate (C{\textendash}S{\textendash}H) ...

Comparison of C{\textendash}S{\textendash}H structural characteristics. (a) Unit cell dimensions, where ...

Comparison of C{\textendash}S{\textendash}H dynamic characteristics. (a) Infrared absorption spectrum ...

Comparison of C{\textendash}S{\textendash}H elastic properties. (a) Elastic constants and the relative ...

}, keywords = {C-S-H, Cement, Simulation, Water model}, issn = {0927-0256}, doi = {10.1016/j.commatsci.2011.08.024}, author = {Qing Ji and Roland Jean-Marc Pellenq and Krystyn J. Van Vliet} } @article {53, title = {Set in stone? A perspective on the concrete sustainability challenge}, journal = {MRS bulletin}, volume = {37}, year = {2012}, month = {Apr-09-2012}, pages = {395{\textendash}402}, abstract = {

As the most abundant engineered material on Earth, concrete is essential to the physical infrastructure of all modern societies. There are no known materials that can replace concrete in terms of cost and availability. There are, however, environmental concerns, including the significant CO2 emissions associated with cement production, which create new incentives for university\–industry collaboration to address concrete sustainability. Herein, we examine one aspect of this challenge\—the translation of scientific understanding at the microscale into industrial innovation at the macroscale\—by seeking improvements in cement-paste processing, performance, and sustainability through control of the mechanisms that govern microstructure development. Specifically, we consider modeling, simulation, and experimental advances in fracture, dissolution, precipitation, and hydration of cement paste precursors, as well as properties of the hardened cement paste within concrete. The aim of such studies is to optimize the chemical reactivity, mechanical performance, and other physical properties of cement paste to enable more sustainable processing routes for this ubiquitous material.

}, doi = {10.1557/mrs.2012.55}, author = {Krystyn J. Van Vliet and Roland Jean-Marc Pellenq and Markus J Buehler and Jeffrey C Grossman and Hamlin M. Jennings and Franz-Josef Ulm and Sidney Yip} } @article {93, title = {Thermodynamics of Water Confined in Porous Calcium-Silicate-Hydrates}, journal = {Langmuir}, volume = {28}, year = {2012}, month = {Aug-07-2012}, pages = {11422-11432}, type = {Article}, abstract = {
Abstract Image

Water within pores of cementitious materials plays a crucial role in the damage processes of cement pastes, particularly in the binding material comprising calcium-silicate-hydrates (C\–S\–H). Here, we employed Grand Canonical Monte Carlo simulations to investigate the properties of water confined at ambient temperature within and between C\–S\–H nanoparticles or \“grains\” as a function of the relative humidity (\%RH). We address the effect of water on the cohesion of cement pastes by computing fluid internal pressures within and between grains as a function of \%RH and intergranular separation distance, from 1 to 10 \Å. We found that, within a C\–S\–H grain and between C\–S\–H grains, pores are completely filled with water for \%RH larger than 20\%. While the cohesion of the cement paste is mainly driven by the calcium ions in the C\–S\–H, water facilitates a disjoining behavior inside a C\–S\–H grain. Between C\–S\–H grains, confined water diminishes or enhances the cohesion of the material depending on the intergranular distance. At very low \%RH, the loss of water increases the cohesion within a C\–S\–H grain and reduces the cohesion between C\–S\–H grains. These findings provide insights into the behavior of C\–S\–H in dry or high-temperature environments, with a loss of cohesion between C\–S\–H grains due to the loss of water content. Such quantification provides the necessary baseline to understand cement paste damaging upon extreme thermal, mechanical, and salt-rich environments.

}, issn = {0743-7463}, doi = {10.1021/la301738p}, author = {Patrick A Bonnaud and Qing Ji and Benoit A. Coasne and Roland Jean-Marc Pellenq and Krystyn J. Van Vliet} } @article {289, title = {An atomistic modelling of the porosity impact on UO2 matrix macroscopic properties}, journal = {Journal of Nuclear Materials}, volume = {415}, year = {2011}, month = {Aug-15-2011}, pages = {210 - 216}, abstract = {

The porosity impact on the UO2 matrix thermomechanical properties was investigated using atomistic simulation techniques. The porosity modifies the thermal expansion coefficient and this is attributed to pore surface effects. The elastic moduli at 0\ K and at finite temperature decrease with porosity, this variation being well approximated using affine functions. These results agree with other mesoscale model predictions and experimental data, showing the ability of the semiempirical potential atomistic simulations to give an overall good description of the porous UO2. However, the surface effects are incompletely described.

Fig. 1. The UO2 elementary cell contains 12 atoms: 4 uranium atoms (large spheres){\textellipsis}

fig.=

Fig. 3. Example of 6{\texttimes}6{\texttimes}6 one pore relaxed supercells of different pore radius (4, 6 and{\textellipsis}

Fig. 4. One layer of UO2 as considered in the present work: top {\textendash} the (100){\textellipsis}

Fig. 5. Variation of the UO2 thermal expansion coefficient versus temperature: top {\textendash}{\textellipsis}

Fig. 6. Variation of the shear modulus (G) and Young{\textquoteright}s modulus (E) versus porosity at 0K

}, issn = {00223115}, doi = {10.1016/j.jnucmat.2011.06.006}, author = {Andrei Jelea and Colbert, M. and F. Ribeiro and G. Tr{\'e}glia and Roland Jean-Marc Pellenq} } @article {256, title = {The scratch test for strength and fracture toughness determination of oil well cements cured at high temperature and pressure}, journal = {Cement and Concrete Research}, volume = {41}, year = {2011}, month = {sept-2011}, pages = {942 - 946}, abstract = {

Recent advances in scratch test analysis provide new ways to relate measured scratch test properties not only to strength properties but fracture properties of materials as well. Herein, we present an application of such tools to oil well cements cured at high temperatures and pressures. We find a concurrent increase of strength and toughness of different oil well cement baseline formulations which we relate to the water-to-binder ratio for a series of cementitious materials prepared with cement and silica flour. The scratch test thus emerges as a self-consistent technique for both cohesive\–frictional strength and fracture properties that is highly reproducible, almost non-destructive, and not more sophisticated than classical compression tests, which makes this \‘old\’ test highly attractive for performance-based field applications.

}, issn = {00088846}, doi = {10.1016/j.cemconres.2011.04.014}, author = {Franz-Josef Ulm and James, Simon} }