Water filling of hydrophilic nanopores

E. DE LA LLAVE; V. MOLINERO; D. A. SCHERLIS

JOURNAL OF CHEMICAL PHYSICS

AMER INST PHYSICS

Año: 2010 vol. 133 p. 34513 - 34522

0021-9606

Molecular dynamics simulations of water in cylindrical hydrophilic pores with diameters of 1.5 and3 nm were performed to explore the phase behavior and the nucleation dynamics of the confinedfluid as a function of the percentage of volume filled f. The interactions of water with the pore wallwere considered to be identical to the interactions between water molecules. At low water contents,all the water is adsorbed to the surface of the pore. A second phase consisting of a liquid plugappears at the onset filling for capillary condensation, f onset = 27% and 34% for the narrow and widepores, respectively. In agreement with experimental results for silica pores, the liquid phase appearsclose to the equilibrium filling f eq in the 1.5 nm pore and under conditions of strong surfacesupersaturations for the 3 nm pore. After condensation, two phases, a liquid plug and asurface-adsorbed phase, coexist in equilibrium. Under conditions of phase coexistence, the watersurface density ⌫coex was found to be independent of the water content and the diameter of the pore.The value of ⌫coex found in the simulations ͑ϳ3 nm−2͒ is in good agreement with experimentalresults for silica pores, suggesting that the interactions of water with silica and with itself arecomparable. The surface-adsorbed phase at coexistence is a sparse monolayer with a structuredominated by small water clusters. We characterize the density and structure of the liquid andsurface phases, the nucleation mechanism of the water plug, and the effect of surface hydrophilicityon the two-phase equilibrium and hysteresis. The results are discussed in light of experiments andprevious simulations.