A comparison of the structure and dynamics of liquid water at hydrophobic and hydrophilic surfaces—a molecular dynamics simulation study

Abstract

The structure and dynamics of liquid water at the interface with three solid surfaces has been investigated via molecular dynamics simulation. The three surfaces include a flat hydrophobic surface, an atomically rough hydrophobic surface, and a contrasting, hydrophilic, fully hydroxylated silica surface. The results of analysis show that, as expected, the solvent near each of the two hydrophobic surfaces behaves essentially equivalently, with loss of hydrogen bonding at the interface. For the hydroxylated surface, surface–solvent hydrogen bonding is stronger than interactions in the bulk solvent, with the nearest solvent layer interacting specifically with up to three surface hydroxyl groups. Nevertheless, distinct structural perturbation of the solvent extends in every case no more than about 10 Å from the surface, and the perturbation is only strong in the immediate solvation layer. Furthermore, the corresponding dynamical perturbation of the solvent, as measured by the diffusion rates and reorientation times in comparison to the bulk, is always relatively small. For the hydrophilic case, it is largest, but even here it is less than a factor of 5 at the immediate interface and less than a factor of 2 in the second hydration layer. The residence time for solvent at the interface is found to be insensitive to the hydrophilicity of the surface. Calculated nuclear magnetic resonance (NMR) order parameters for the solvent are found to reflect solvent orientational ordering, but are shown not to be distinctive of the nature of that order.

Effect of Surface Polarity on the Structure and Dynamics of Water in Nanoscale Confinement

“…The hindered mobility of water molecules confined by hydrophilic surfaces (k ) 1.0) has been observed with similar confining surfaces and was attributed to the strong HB interactions between water and surface silanol groups. 29 The slow translational dynamics observed at k ) 0.0, however, seems counterintuitive at first sight given the comparatively weaker water-substrate interactions. Fast interfacial dynamics have been observed for TIP4P and TIP5P water 29,47 and for a Lennard-Jones fluid 48 confined by perfectly flat hydrophobic surfaces, while the dynamics of a Lennard-Jones fluid confined by a rough hydrophobic surface appear to slow down.…”

“…43 Nevertheless, we choose to model the metastable -cristobalite phase because an accurate force field for this type of surface has been developed previously. 29 As part of an ongoing research effort we plan to investigate the effects of changing the surface structure to that of the stable phase, R-cristobalite, in addition to amorphous silica and silica gels; as well as the inclusion of surface defects, which have been shown to affect water adsorption. 44 We will also study the effect of substrate flexibility (vide infra).…”

Phase diagram of water between hydrophobic surfaces

“…The parameters C 9 and C 3 are those chosen for the interaction between a water molecule and a "hydrophobic" solid surface. 5 The potential function v͑z͒ is zero at the distance z 0 = ͑C 9 / C 3 ͒ 1/6 = 2.47 Å and rapidly increases at shorter distances. In Fig.…”

“…There are many computational studies on confined water, [4][5][6][7][8][9][10][11][12] some of the pioneering works date back to 1980s. 4 One of the earlier computer simulations focusing on liquidsolid phase transitions 13 showed that water between hydrophobic surfaces freezes into a bilayer form of crystalline ice when temperature is lowered under a fixed normal pressure.…”

Insights into the behavioral difference of water in the presence of GM1

“…In bio-mimicking systems such as in micelles, reverse micelles, the structure and dynamics of water were also investigated [22][23][24]. Beside experiments, computer simulation also aids to understand the interfacial properties of water molecules [25,26]. The orientation and polarization of the interfacial water [27][28][29][30][31][32], water conductance through carbon nanotube [33], the hydrogen bonding structure of water and of the lipid headgroups has also been assessed [32,34,35] using MD simulations.…”