Molecular Dynamics Simulation Study of Interaction between Model Rough Hydrophobic Surfaces

TL;DR

This study uses molecular dynamics simulations to explore how surface roughness and flexibility influence hydrophobic interactions between model surfaces, revealing the role of water and surface properties in these interactions.

Contribution

The paper introduces a modified model of hydrophobic surfaces by removing charges from polar headgroups, highlighting the impact of roughness and flexibility on hydrophobic interactions.

Findings

Water mediates attractive hydrophobic interactions.

Surface roughness enhances hydrophobic effects.

A shallow minimum in PMF relates to headgroup flexibility.

Abstract

We study some aspects of hydrophobic interaction between molecular rough and flexible model surfaces. The model we use in this work is based on a model we used previously (Eun, C.; Berkowitz, M. L. J. Phys. Chem. B 2009, 113, 13222-13228), when we studied the interaction between model patches of lipid membranes. Our original model consisted of two graphene plates with attached polar headgroups; the plates were immersed in a water bath. The interaction between such plates can be considered as an example of a hydrophilic interaction. In the present work we modify our previous model by removing the charge from the zwitterionic headgroups. As a result of this procedure, the plate character changes; it becomes hydrophobic. By separating the total interaction (or potential of mean force, PMF) between plates into the direct and the water-mediated interactions we observe that the latter changes from repulsive to attractive, clearly emphasizing the important role of water as a medium. We also investigate the effect of roughness and flexibility of the headgroups on the interaction between plates and observe that roughness enhances the character of the hydrophobic interaction. The presence of a dewetting transition in a confined space between charge-removed plates confirms that the interaction between plates is strongly hydrophobic. In addition, we notice that there is a shallow local minimum in the PMF in case of charge-removed plates. We find that this minimum is associated with the configurational changes that flexible headgroups undergo, as the two plates are brought together.