Water adsorption in disordered mesoporous silica (Vycor) at 300K and 650K: A Grand Canonical Monte Carlo simulation study of hysteresis

Puibasset, Joël; Pellenq, Roland J.‐M.

doi:10.1063/1.1854129

Cited by 83 publications

(71 citation statements)

References 52 publications

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“…6 Configurational energy of water adsorbed in silicalite-1 as a function of relative pressure sists, and the number of free sites decreases significantly. Interestingly, the opposite behavior was observed in the case of water adsorption in hydrophilic mesoporous Vycor material (Puibasset and Pellenq 2005).…”

Section: Simulation Resultsmentioning

confidence: 92%

Molecular simulations of water in hydrophobic microporous solids

2008

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This work reports Grand Canonical Monte-Carlo molecular simulation (GCMC) results of water adsorption in a priori hydrophobic microporous solids such as silicalite, a purely siliceous zeolite (Ø pore ∼ 5 Å) and C-Y, a pure carbon replica of zeolite Y (Ø pore ∼ 1 nm). At a first step, in both cases, the water-water interactions are described with the SPC model (calibrated for bulk liquid water) while watersubstrate interactions are calculated within the framework of the PN-TrAZ model. This adsorbate-zeolite potential decomposes into short range (repulsive, inductive and dispersive) interaction terms with transferable parameters plus, in the case of silicalite, an electrostatic interaction term based on SPC partial charges for water and ab initio charges for silicalite. With such a standard approach, we found that water fills the microporous volume in both materials at pressure value well below P 0 ; hence does not show a strong hydrophobic behaviour at variance with reference experiments (V. Eroshenko et al. in C. R. Phys. 3:111, 2002). This indicates that common models used to describe confined polar molecules are far from being operative. We show on the basis of periodic ab initio calculations that confined water molecules in silicate have a dipole value ∼10% smaller than that in the 3D liquid phase indicating that the environment felt by a confined water molecule in silicalite pores is not equivalent to that in the bulk liquid. This implies that classical simulations of polar molecules in ultra

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Section: Simulation Resultsmentioning

confidence: 92%

Molecular simulations of water in hydrophobic microporous solids

2008

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“…An equal number of attempts for translation, rotation, creation or destruction of molecules was chosen. The isotherm was calculated for 300 K. Acknowledging the very restricted available space in between tobermoritic layers, one should not expect capillary condensation to occur in contrast to larger pore systems such as vycor (43). In our case, the adsorption/desorption process is expected to be close to that observed for microporous zeolite as far as water adsorption is concerned (44).…”

Section: From Energy Minimization To Elastic Properties Using Empiricmentioning

confidence: 99%

A realistic molecular model of cement hydrates

Pellenq

Kushima²,

Shahsavari³

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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786

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Despite decades of studies of calcium-silicate-hydrate (C-S-H), the structurally complex binder phase of concrete, the interplay between chemical composition and density remains essentially unexplored. Together these characteristics of C-S-H define and modulate the physical and mechanical properties of this ''liquid stone'' gel phase. With the recent determination of the calcium/silicon (C/S ‫؍‬ 1.7) ratio and the density of the C-S-H particle (2.6 g/cm 3 ) by neutron scattering measurements, there is new urgency to the challenge of explaining these essential properties. Here we propose a molecular model of C-S-H based on a bottom-up atomistic simulation approach that considers only the chemical specificity of the system as the overriding constraint. By allowing for short silica chains distributed as monomers, dimers, and pentamers, this C-S-H archetype of a molecular description of interacting CaO, SiO2, and H2O units provides not only realistic values of the C/S ratio and the density computed by grand canonical Monte Carlo simulation of water adsorption at 300 K. The model, with a chemical composition of (CaO)1.65(SiO2)(H2O)1.75, also predicts other essential structural features and fundamental physical properties amenable to experimental validation, which suggest that the C-S-H gel structure includes both glass-like short-range order and crystalline features of the mineral tobermorite. Additionally, we probe the mechanical stiffness, strength, and hydrolytic shear response of our molecular model, as compared to experimentally measured properties of C-S-H. The latter results illustrate the prospect of treating cement on equal footing with metals and ceramics in the current application of mechanism-based models and multiscale simulations to study inelastic deformation and cracking.atomistic simulation ͉ mechanical properties ͉ structural properties B y mixing water and cement, a complex hydrated oxide called calcium-silicate-hydrate (C-S-H) precipitates as nanoscale clusters of particles (1). Much of our knowledge of C-S-H has been obtained from structural comparisons with crystalline calcium silicate hydrates, based on HFW Taylor's postulate that real C-S-H was a structurally imperfect layered hybrid of two natural mineral analogs (2) (4)]. While this suggestion is plausible in morphological terms, this model is incompatible with two basic characteristics of real C-S-H; specifically the calcium-tosilicon ratio (C/S) and the density. Recently, small-angle neutron scattering measurements have fixed the C/S ratio at 1.7 and the density at 2.6 g/cm 3 (1), values that clearly cannot be obtained from either tobermorite (C/S ϭ 0.83, 2.18 g/cm 3 ) or jennite (C/S ϭ 1.5 and 2.27 g/cm 3 ). From the standpoint of constructing a molecular model of C-S-H, this means that these crystalline minerals are not strict structural analogs. Here we adopt the perspective that the chemical composition of C-S-H is the most essential property in formulating a realistic molecular description. We show that once the C/S ratio is described...

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“…The bimodal water filing is related to the bimodal strength of the water/surface interactions, and it is analyzed by the isosteric heat of adsorption [47]. Using Eq.…”

Section: Bimodal Water Fillingmentioning

confidence: 99%

Role of water states on water uptake and proton transport in Nafion using molecular simulations and bimodal network

Hwang

Kaviany

Gostick

et al. 2011

Polymer

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Using molecular simulations and a bimodal domain network, the role of water state on Nafion water uptake and water and proton transport is investigated.Although the smaller domains provide moderate transport pathways, their effectiveness remains low due to strong, resistive water molecules/domain surface interactions. The water occupancy of the larger domains yields bulk-like water, and causes the observed transition in the water uptake and significant increases in transport properties.

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Water adsorption in disordered mesoporous silica (Vycor) at 300K and 650K: A Grand Canonical Monte Carlo simulation study of hysteresis

Cited by 83 publications

References 52 publications

Molecular simulations of water in hydrophobic microporous solids

Molecular simulations of water in hydrophobic microporous solids

A realistic molecular model of cement hydrates

Role of water states on water uptake and proton transport in Nafion using molecular simulations and bimodal network

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