@article {76, title = {Molecular intermittent dynamics of interfacial water: probing adsorption and bulk confinement}, journal = {Soft Matter}, volume = {9}, year = {2013}, month = {Jul-26-2013}, pages = {8654-8663}, type = {Article}}, abstract = {

Numerous natural and manufactured systems such as colloidal suspensions, geological pore networks, catalysts, and nanofluidic devices develop a large and sometimes complex interface strongly influencing the dynamics of the fluid entrapped inside these materials. A coarse grain picture of this molecular dynamics can be considered as an intermittence of adsorption steps and bulk relocations from one point to another point of the interface. Adsorption statistics such as the adsorption time distribution and its first moment reflect the degree of interaction of the molecule with the colloidal interface. Relocation statistics strongly depend on the shape of the pore, the surface forces and the bulk confinement. In this paper, a theoretical analysis of this intermittent dynamics is presented. A direct comparison with molecular dynamics simulations is proposed in the case of liquid water confined inside a hydrophilic substrate (silica slit pore with hydroxylated surfaces) or inside a hydrophobic substrate (carbon nanotube). Analysis of this intermittent dynamics allows quantification of the level of interaction of the vicinal water with the solid interface inside an independent adsorption region in exchange with the confined bulk fluid. The possibility of experimentally probing this dynamics using NMR relaxometry is emphasized.

}, issn = {1744-683X}, doi = {10.1039/c3sm51940f}, author = {Pierre E. Levitz and Patrick A Bonnaud and Pierre-Andre Cazade and Roland Jean-Marc Pellenq and Benoit A. Coasne} } @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 {49, title = {Solvated calcium ions in charged silica nanopores}, journal = {The Journal of Chemical Physics}, volume = {137}, year = {2012}, month = {Aug-14-2012}, pages = {Article Number: 064706}, abstract = {

Hydroxyl surface density in porous silica drops down to nearly zero when the pH of the confined aqueous solution is greater than 10.5. To study such extreme conditions, we developed a model of slit silicananopores where all the hydrogen atoms of the hydroxylated surface are removed and the negative charge of the resulting oxygen dangling bonds is compensated by Ca2+ counterions. We employed grand canonical Monte Carlo and molecular dynamics simulations to address how the Ca2+ counterions affect the thermodynamics, structure, and dynamics of confined water. While most of the Ca2+ counterions arrange themselves according to the so-called \“Stern layer,\” no diffuse layer is observed. The presence of Ca2+ counterions affects the pore filling for strong confinement where the surfaceeffects are large. At full loading, no significant changes are observed in the layering of the first two adsorbed water layers compared to nanopores with fully hydroxylated surfaces. However, the water structure and water orientational ordering with respect to the surface is much more disturbed. Due to the super hydrophilicity of the Ca2+-silica nanopores,waterdynamics is slowed down and vicinal water molecules stick to the pore surface over longer times than in the case of hydroxylated silicasurfaces. These findings, which suggest the breakdown of the linear Poisson\–Boltzmann theory, provide important information about the properties of nanoconfined electrolytes upon extreme conditions where the surface charge and ion concentration are large.

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}, doi = {10.1063/1.4742854}, author = {Patrick A Bonnaud and Benoit A. Coasne and Roland Jean-Marc Pellenq} } @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 = {
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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} }