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Probing Realistic Water-2D Material Interfaces via Combined Quantum and Classical Simulations

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If you have a question about this talk, please contact Dr Venkat Kapil.

Two-dimensional (2D) materials are gaining increasing attention for use in seawater desalination, osmotic power harvesting, and biological sensing devices. Because water comes into close contact with 2D material surfaces in these applications, it is important to understand water-2D material interactions at the molecular level. At the same time, 2D materials often have vacancies and roughness in them, and thus understanding their effect on interfacial properties is crucial to model such interfaces realistically. In this talk, I will highlight our recent work on the combined use of quantum-mechanical density functional theory (DFT) calculations and classical molecular dynamics (MD) simulations to probe water-2D material interfaces. While DFT calculations can be used to predict the distribution of charge inside defective 2D materials, MD simulations can be used to simulate the thermodynamic and transport properties of interfacial water.

I will discuss the effect of vacancy defects and surface roughness on the wettability and slip length of water on hexagonal boron nitride (hBN), a prominent 2D material. At the molecular level, the no-slip boundary condition is violated, as quantified by the slip length of water on the surface. I will show that vacancies at a lower concentration of 0.082 nm-2 do not affect the wettability of hBN, although they still affect the water slip length. On the other hand, vacancies at a larger concentration of 0.32 nm-2 affect interfacial properties significantly. In fact, nitrogen vacancies at such concentrations can increase the slip length of water on hBN threefold to around 18 nm, presenting defective hBN as an alternative high-slip surface to graphene. I will also demonstrate how surface roughness in hBN can explain the water contact angle of 66° and water slip length of 1 nm measured experimentally, highlighting the prominent role played by electrostatic interactions in the interfacial properties of water on realistic hBN surfaces. Overall, these multi-scale investigations of thermodynamic and transport properties offer new insights into the wettability of defective 2D material surfaces and water flow on them.

This talk is part of the Lennard-Jones Centre series.

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