On the influence of the intermolecular potential on the wetting properties of water on silica surfaces

Abstract

We study the wetting properties of water on silica surfaces using molecular dynamics (MD) simulations. To describe the intermolecular interaction between water and silica atoms, two types of interaction potential models are used: the standard Bródka and Zerda (BZ) model, and the Gulmen and Thompson (GT) model. We perform an in-depth analysis of the influence of the choice of the potential on the arrangement of the water molecules in partially filled pores and on top of silica slabs. We find that at moderate pore filling ratios, the GT silica surface is completely wetted by water molecules, which agrees well with experimental findings, while the commonly used BZ surface is less hydrophilic and is only partially wetted. We interpret our simulation results using an analytical calculation of the phase diagram of water in partially filled pores. Moreover, an evaluation of the contact angle of the water droplet on top of the silica slab reveals that the interaction becomes more hydrophilic with increasing slab thickness and saturates around 2.5 − 3 nm, in agreement with the experimentally found value. Our analysis also shows that the hydroaffinity of the surface is mainly determined by the electrostatic interaction, but that the van der Waals interaction nevertheless is strong enough that it can turn a hydrophobic surface into a hydrophilic surface.

Oil Contact Angles in a Water-Decane-Silicon Dioxide System: Effects of Surface Charge

“…It is noted that in the validation simulation, the hydroxyl groups on the surface of silicon dioxide substrates are fixed as other representative works done. The measured contact angle is 7.8°, which is in good agreement with that in the work by Pafong et al [ 37 ]. They reported a water contact angle of 7.0°, which presents a relative deviation of only 10.3%.…”

Mixtures of Alcohols and Water confined in Mesoporous Silica: A Combined Solid-State NMR and Molecular Dynamics Simulation Study

“…In Figure S6, it is shown that water molecules prefer to stay near the pore wall. 87 Furthermore, from Figures 7 and S5 a bilayer formation is assumed, as the length of the 1-octanol molecule is roughly 0.9 nm. Therefore, two layers of 1-octanol molecules that interact via their hydrophobic aliphatic chains may arrange inside the pore as illustrated schematically in Figure 6b.…”

“…To confirm the latter, we performed a simulation with only water and no 1-octanol in the pore at 15% pore filling. In Figure S6, it is shown that water molecules prefer to stay near the pore wall . Furthermore, from Figures and S5 a bilayer formation is assumed, as the length of the 1-octanol molecule is roughly 0.9 nm.…”

Bulk supercooled water versus adsorbed films on silica surfaces: specific heat by Monte Carlo simulation

“…28 Our still crude model of hydrophilic surface is unable to catch these phenomena, and deserve further studies. Several directions are privileged: (i) considering more realistic amorphous silica surfaces, with a degree of hydroxylation closer to Vycor surfaces (16 OH/nm 2 ) 22 and possibly including disorder, [54][55][56] which favors the formation of clusters that are believed to play an important role; (ii) studying the effect of the geometry of the water/silica interface, since this is known to influence water properties, in particular in small pores; (iii) improving the water-silica interaction model, since it has been shown that the hydrophilic properties of silica are much more sensitive to the potential than the surface hydroxyl density; 44,97 and, (iv) improving the silica interatomic potential, in particular regarding the dynamics of the silanol groups interacting with water.…”