TY - JOUR
T1 - Solvated calcium ions in charged silica nanopores
AU - Bonnaud, Patrick A.
AU - Coasne, Benoît
AU - Pellenq, Roland J.M.
N1 - Funding Information:
We wish to thank the CNRS-ATILH Contrat de Programme de Recherche: Résistance, Porosité et Transport des Matériaux Cimentaires for financial support. Calculations were performed using supercomputers at the Institut de Développement et des Ressources en Informatique Scientifique (IDRIS, CNRS, Grant No. 96223). We are indebted to Pierre-Andre Cazade, Qing Ji, Patrick Ganster, Olivier Coussy (the late), Krystyn Van Vliet, Pierre Levitz, and Dominique Petit for very fruitful discussions.
PY - 2012/8/14
Y1 - 2012/8/14
N2 - 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 silica nanopores where all the hydrogen atoms of the hydroxylated surface are removed and the negative charge of the resulting oxygen dangling bonds is compensated by Ca 2 counterions. We employed grand canonical Monte Carlo and molecular dynamics simulations to address how the Ca 2 counterions affect the thermodynamics, structure, and dynamics of confined water. While most of the Ca 2 counterions arrange themselves according to the so-called Stern layer, no diffuse layer is observed. The presence of Ca 2 counterions affects the pore filling for strong confinement where the surface effects 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 Ca 2-silica nanopores, water dynamics is slowed down and vicinal water molecules stick to the pore surface over longer times than in the case of hydroxylated silica surfaces. 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.
AB - 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 silica nanopores where all the hydrogen atoms of the hydroxylated surface are removed and the negative charge of the resulting oxygen dangling bonds is compensated by Ca 2 counterions. We employed grand canonical Monte Carlo and molecular dynamics simulations to address how the Ca 2 counterions affect the thermodynamics, structure, and dynamics of confined water. While most of the Ca 2 counterions arrange themselves according to the so-called Stern layer, no diffuse layer is observed. The presence of Ca 2 counterions affects the pore filling for strong confinement where the surface effects 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 Ca 2-silica nanopores, water dynamics is slowed down and vicinal water molecules stick to the pore surface over longer times than in the case of hydroxylated silica surfaces. 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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U2 - 10.1063/1.4742854
DO - 10.1063/1.4742854
M3 - Article
AN - SCOPUS:84865172618
VL - 137
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
SN - 0021-9606
IS - 6
M1 - 064706
ER -