2024 AIChE Annual Meeting

(364h) Development of All-Atomistic Force Fields to Model the Polarization Interactions of Liquids with Hexagonal Boron Nitride and Boron Nitride Nanotubes

Author

Research Interests: computer simulations and multiscale modeling of nanoscale transport and phase transitions

Recent advances in synthesis techniques have led to the development of a variety of nanostructured boron nitride (BN) materials, including hexagonal boron nitride (hBN) and boron nitride nanotubes (BNNTs), which exhibit a range of novel properties. Molecular dynamics (MD) simulations offer a powerful tool for exploring the interfacial properties of BN nanomaterials at the molecular level. Specifically, they enable detailed analysis of chemical structures and intermolecular interaction energies, properties which often pose significant challenges for experimental investigation. However, to ensure reliable simulations, it is essential to utilize suitable force fields that accurately model the underlying intermolecular interactions. The modeling of interactions between BN materials and liquids has garnered significant interest. Various approaches have been employed to develop force field parameters for these models, including the use of the Lorentz–Berthelot combining rule, quantum chemical simulations, and machine learning techniques. It is important to note that at any solid/water interface, the polar nature of water and the charged characteristic of salt ions can generate substantial electric fields, leading to considerable electronic polarization of the solid surface. The induced polarization of carbon atoms in carbon-based nanomaterials, such as graphene and carbon nanotubes, has been incorporated into molecular dynamics (MD) simulations through polarizable force fields[1-4]. These simulations underscore the importance of accounting for many-body polarization effects to accurately understand and model interfacial phenomena in these materials. While the out-of-plane polarizability of a monolayer of hBN is similar to that of graphene, hBN is different being a heteropolar 2D material with boron and nitrogen atoms carrying partial atomic charges. Furthermore, self-consistently modeling the polarizations of the boron and nitrogen atoms remains an unresolved challenge in existing MD simulation studies, leading to a gap in the molecular-level understanding of polarization effects at hBN-water interfaces.

In this study, we developed a series of polarizable force fields to accurately model the polarization effects at BN-water interfaces, covering both planar hBN interfaces[5] and cases involving nanotube confinement. To this end, the polarization response of planar hBN and BNNTs are modeled using three parameters: the static dipole polarizability of the boron atom, the static dipole polarizability of the nitrogen atom, and the Thole damping parameter which governs the electrostatic interactions between the induced dipoles. We self-consistently derived these polarizability parameters to accurately reproduce the anisotropic polarizability tensors of periodic hBN layers and BNNTs. This polarizable force field model is the first of its kind to self-consistently account for electronic polarization effects at the BN-water interface, including the prediction of binding energies of a water molecule interacting with hBN that closely match those obtained from Diffusion Monte Carlo (DMC) simulations [6].

Next, we used the developed polarizable force field to carry out MD simulations of water on multilayered hBN. The simulated contact angle, 83.1◦, derived from the work of adhesion between hBN and water, is in very good agreement with the recent experimentally measured value of 79.0◦ [7]. Furthermore, we explored how polarization effects influence ion adsorption at hBN interfaces, considering various ion types and charges. Our findings reveal that while the polarization energy between hBN and ions is significantly high in vacuum, this polarization energy is substantially reduced by over 80% when water molecules are present at the hBN interface. This water-mediated screening of the polarization energy has a significant influence in dictating the free energy of ion adsorption at the hBN/water interface. Additionally, we have extended the theoretical framework for planar hBN surfaces to model BNNTs where the polarizability parameters are nearly invariant with respect to the nanotube radius unlike in the case of carbon nanotubes where there is a pronounced curvature dependence[4]. This offers exciting opportunities to tune water and ion transport at the nanoscale based on the electronic properties of the confining 1D nanomaterials.

References

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