Theoretical Approach to study structure of Water at the Solid-Water Interface

Water is crucial for human life. The interaction of water with the solid material surface is ubiquitous. In the early days of our planet such interactions may have given rise to the creation of prebiotic organic matter. Various physiochemical processes such as wastewater teatment, corrosion,wetting, mineral dissolution etc. are governed by the solid-water interaction at the interface. Water molecules at interfaces have different properties than their bulk counterparts due to the abrupt break in the bulk hydrogen bonding network caused by the presence of a phase boundary. Yet as crucial as these interfaces are, our knowledge of what takes place at the molecular-level where water meets solid isn’t ample. In the present study, the distinctive ordering of the first layer of water molecules at the interface for different hydrophobic/hydrophilic solid surfaces is targeted via molecular dynamics(MD) simulation approach using LAMMPS Software to gather the molecular-level insight [1].

Density curve is observed first for hydrophobic surfaces which can be further classified into two regimes namely non-wetting and wetting regime [2]. In the non-wetting regime, water density variation is similar to the air-water interface. It increases slighty from nil value to the bulk value as we move towards the bulk. For the wetting regime, water density shows a sigmoidal variation around the bulk value. The amplitude of this curve varies inversely with the hydrophocity of the surface. This regime points out that just next to the interface few water layers with density peaks and dips exist. A transition between the wetting and non-wetting regime occurs around contact angle ~130 degree. For hydrophilic surfaces, the water density oscillations narrowed down to single sharp peak after which the curve drops down to nil value with incease in distance from the interface. For surfaces which are neither extremely hydrophobic/hydrophilic, water density curve is an interplay between hydrophilic water density curve and wetting regime curve.

We will give a detailed analysis of our results on water contact angle and density variation curve for interfacial water on varying nature of solid surface. This analysis can be used to pick out surface materials with desirable hydrophobic/hydrophilic traits depending on the purpose such as preventing rusting and corrosion or selecting a material which will act as a good biosensor.

References

1. Meysam Makaremi, Myung S. Jhon, Meagan S. Mauter and Lorenz T. Biegler; J. Phys. Chem. C 2016, 120, 11528–11534.
2. Travis G. Trudeau, Kailash C. Jena and Dennis K. Hore; J. Phys. Chem. C 2009, 113, 20002–20008.
3. Shalaka Dewan, Vincenzo Carnevale, Arindam Bankura, Ali Eftekhari-Bafrooei, Giacomo Fiorin, Michael L.Klein and Eric Borguet;Langmuir 2014, 30, 8056–8065.
4. Bo Shi and Vijay K. Dhira; J. Chem. Phys. 2009, 130, 034705.
5. Jianwei Wang, Andrey G. Kalinichev, R. James Kirkpatrickand Randall T. Cygan; J. Phys. Chem. B 2005, 109, 15893-15905.