The interaction between hexagonal boron nitride and water from first principles

Modulating the Water Contact Angle Using Surface Roughness: Interfacial Properties of Hexagonal Boron Nitride Surfaces

Hexagonal boron nitride (hBN) exhibits immense potential in H2O-related technologies, but its interaction with H2O, especially on rough surfaces, remains unclear. This study unravels the influence of surface roughness and force field selection on hBN wettability using molecular dynamics (MD) simulations. We leverage quantum mechanical calculations to accurately capture the hBN surface charge distribution and combine it with free energy calculations via MD simulations for the hBN-H2O interfaces. Incorporating surface roughness into the model yields results in close agreement with the experimental contact angle of 66° for H2O using FF-3 force fields, validating the simulation approach. However, this approach can yield an unrealistic water contact angle (WCA) of 0° for FF-2 force fields, highlighting the crucial role of force field selection and realistic surface representations. We further dissect the impact of roughness on the WCA, identifying the individual contributions of electrostatic and Lennard-Jones interactions to the work of adhesion. This research investigates the combined impact of surface roughness and force fields on interfacial properties, providing new possibilities for the advancement and optimization of desalination.

Water Electric Field Induced Modulation of the Wetting of Hexagonal Boron Nitride: Insights from Multiscale Modeling of Many-Body Polarization

Understanding the behavior of water contacting two-dimensional materials, such as hexagonal boron nitride (hBN), is important in practical applications, including seawater desalination and energy harvesting. Water, being a polar solvent, can strongly polarize the hBN surface via the electric fields that it generates. However, there is a lack of molecular-level understanding about the role of polarization effects at the hBN/water interface, including its effect on the wetting properties of water. In this study, we develop a theoretical framework that introduces an all-atomistic polarizable force field to accurately model the interactions of water molecules with hBN surfaces. The force field is then utilized to self-consistently describe the water-induced polarization of hBN using the classical Drude oscillator model, including predicting the hBN-water binding energies which are found to be in excellent agreement with diffusion Monte Carlo (DMC) predictions. By carrying out molecular dynamics (MD) simulations, we demonstrate that the polarizable force field yields a water contact angle on multilayered hBN which is in close agreement with the recent experimentally reported values. Conversely, an implicit modeling of the hBN-water polarization energy utilizing a Lennard-Jones (LJ) potential, a commonly utilized approximation in previous MD simulation studies, leads to a considerably lower water contact angle. This difference in the predicted contact angles is attributed to the significant energy-entropy compensation resulting from the incorporation of polarization effects at the hBN-water interface. Our work highlights the importance of self-consistently modeling the hBN-water polarization energy and offers insights into the wetting-related interfacial phenomena of water on polarizable materials.

Anisotropic Interfacial Force Field for Interfaces of Water with Hexagonal Boron Nitride

This study introduces an anisotropic interfacial potential that provides an accurate description of the van der Waals (vdW) interactions between water and hexagonal boron nitride (h-BN) at their interface. Benchmarked against the strongly constrained and appropriately normed functional, the developed force field demonstrates remarkable consistency with reference data sets, including binding energy curves and sliding potential energy surfaces for various configurations involving a water molecule adsorbed atop the h-BN surface. These findings highlight the significant improvement achieved by the developed force field in empirically describing the anisotropic vdW interactions of the water/h-BN heterointerfaces. Utilizing this anisotropic force field, molecular dynamics simulations demonstrate that atomically flat, pristine h-BN exhibits inherent hydrophobicity. However, when atomic-step surface roughness is introduced, the wettability of h-BN undergoes a significant change, leading to a hydrophilic nature. The calculated water contact angle (WCA) for the roughened h-BN surface is approximately 64°, which closely aligns with experimental WCA values ranging from 52° to 67°. These findings indicate the high probability of the presence of atomic steps on the surfaces of the experimental h-BN samples, emphasizing the need for further experimental verification. The development of the anisotropic interfacial force field for accurately describing interactions at the water/h-BN heterointerfaces is a significant advancement in accurately simulating the wettability of two-dimensional (2D) materials, offering a reliable tool for studying the dynamic and transport properties of water at these interfaces, with implications for materials science and nanotechnology.

Exploring the electron donor-acceptor duality of B3N3 in noncovalent interactions

Boron nitrides are very important and are used as lubricants, insulating agents, etc. Interactions of such systems with small molecules are important. This study examined the potential of B3N3 (triboron trinitride) to act as both an electron acceptor and an electron donor in the formation of noncovalent interactions. The anisotropic electronic distribution observed in the electrostatic potential map supported the B3N3's ability to exhibit the predicted electron donor-acceptor duality. Further computational investigations on optimized gas-phase complexes of B3N3:(NH3)n=1-3, B3N3:(NCH)n=1-6, B3N3:(N2H2)n=1-3 and (B3N3)2 confirmed that the B3N3 molecule can participate in B⋯N triel bonding interactions and H···N hydrogen bonding interactions. These energetically stable complexes are primarily governed by electrostatic and polarization interactions.

Water adsorption and dynamics on graphene and other 2D materials: Computational and experimental advances

The interaction of water and surfaces, at molecular level, is of critical importance for understanding processes such as corrosion, friction, catalysis and mass transport. The significant literature on interactions with single crystal metal surfaces should not obscure unknowns in the unique behaviour of ice and the complex relationships between adsorption, diffusion and long-range inter-molecular interactions. Even less is known about the atomic-scale behaviour of water on novel, non-metallic interfaces, in particular on graphene and other 2D materials. In this manuscript, we review recent progress in the characterisation of water adsorption on 2D materials, with a focus on the nano-material graphene and graphitic nanostructures; materials which are of paramount importance for separation technologies, electrochemistry and catalysis, to name a few. The adsorption of water on graphene has also become one of the benchmark systems for modern computational methods, in particular dispersion-corrected density functional theory (DFT). We then review recent experimental and theoretical advances in studying the single-molecular motion of water at surfaces, with a special emphasis on scattering approaches as they allow an unparalleled window of observation to water surface motion, including diffusion, vibration and self-assembly.

ReaxFF reactive molecular dynamics simulations to study the interfacial dynamics between defective h-BN nanosheets and water nanodroplets

In this work, the authors have developed a reactive force field (ReaxFF) to investigate the effect of water molecules on the interfacial interactions with vacancy defective hexagonal boron nitride (h-BN) nanosheets by introducing parameters suitable for the B/N/O/H chemistry. Initially, molecular dynamics simulations were performed to validate the structural stability and hydrophobic nature of h-BN nanosheets. The water molecule dissociation mechanism in the vicinity of vacancy defective h-BN nanosheets was investigated, and it was shown that the terminal nitrogen and boron atoms bond with a hydrogen atom and hydroxyl group, respectively. Furthermore, it is predicted that the water molecules arrange themselves in layers when compressed in between two h-BN nanosheets, and the h-BN nanosheet fracture nucleates from the vacancy defect site. Simulations at elevated temperatures were carried out to explore the water molecule trajectory near the functionalized h-BN pores, and it was observed that the intermolecular hydrogen bonds lead to agglomeration of water molecules near these pores when the temperature was lowered to room temperature. The study was extended to observe the effect of pore sizes and temperatures on the contact angle made by a water nanodroplet on h-BN nanosheets, and it was concluded that the contact angle would be less at higher temperatures and larger pore sizes. This study provides important information for the use of h-BN nanosheets in nanodevices for water desalination and underwater applications, as these h-BN nanosheets possess the desired adsorption capability and structural stability.

On the wetting translucency of hexagonal boron nitride

When a drop sits on an atomically thin coating supported by a hydrophilic material, it is possible that the underlying substrate influences the equilibrium contact angle. Such behavior is known as the wetting translucency effect.

A Bespoke Force Field To Describe Biomolecule Adsorption at the Aqueous Boron Nitride Interface

Reliable manipulation of the interface between 2D nanomaterials and biomolecules represents a current frontier in nanoscience. The ability to resolve the molecular-level structures of these biointerfaces would provide a fundamental data set that is needed to enable systematic and knowledge-based progress in this area. These structures are challenging to obtain via experiment alone, and molecular simulations offer a complementary approach to address this problem. Compared with graphene, the interface between hexagonal boron nitride (h-BN) and biomolecules is relatively understudied at present. While several force fields are currently available for modeling the h-BN/water interface, there is a lack of a suitable force field that can describe the interactions between h-BN, liquid water, and biomolecules. Here, we use density functional theory calculations to create a force field, BoNi-CHARMM, to describe biomolecular interactions at the aqueous h-BN interface. Verifying our force field presents an additional challenge, given the scarcity of available experimental data for these interfaces. We test our force field against experimental evidence regarding the water/surface contact angle and confirm that the force field provides experimentally consistent values. We also present preliminary data regarding predictions of the free energy of adsorption of a selection of amino acids at the aqueous h-BN interface, revealing arginine and tryptophan to be among the strongest binders. This force field provides an opportunity to initiate a systematic progression in our current understanding of how to capture the intermolecular interactions at the h-BN biointerface.

Liquids with Lower Wettability Can Exhibit Higher Friction on Hexagonal Boron Nitride: The Intriguing Role of Solid-Liquid Electrostatic Interactions

We investigate the wetting and frictional behavior of polar (water and ethylene glycol) and nonpolar (diiodomethane) liquids on the basal plane of hexagonal boron nitride (hBN) using molecular dynamics simulations. Our results for the wettability of water on the hBN basal plane (contact angle 81°) are in qualitative agreement with the experimentally deduced mild hydrophilicity of the hBN basal plane (contact angle 66°). We find that water exhibits the lowest wettability, as quantified by the highest contact angle, but the highest friction coefficient of (1.9 ± 0.4) × 10⁵ N-s/m³ on the hBN basal plane among the three liquids considered. This intriguing finding is explained in terms of the competition between dispersion and electrostatic interactions operating between the hBN basal plane and the three liquids. We find that electrostatic interactions do not affect the wetting behavior appreciably, as quantified by a less than 3° change in the respective contact angles of the three liquids considered. On the other hand, electrostatic interactions are found to increase the friction coefficients of the three liquids in contact with hBN to different extents, indicating that despite the increased friction of water on hBN, relative to that on graphene, nonpolar liquids may exhibit similar friction coefficients on hBN and graphene. Our findings reveal that the increase in the friction coefficient, upon incorporation of solid-liquid electrostatic interactions, is brought about by a greater increase in the solid-liquid mean-squared total lateral force, as compared to a smaller reduction in the decorrelation time of the solid-liquid force.

Electrowetting on 2D dielectrics: a quantum molecular dynamics investigation

Electrowetting on dielectrics (EWOD) is widely used to manipulate the spreading of a conductive liquid on a dielectric surface by applying an electric field. 2D hydrophobic dielectrics are promising candidates for EWOD applications. In this study, extensive quantum molecular dynamics (MD) simulations are performed to investigate the electrowetting behavior of salty water on hexagonal boron nitride (h-BN) monolayer. The proximal adsorption of salt ions and the associated realignment of the dipole moments of interfacial water with the applied electric field are found to be the physical origin of the electrowetting behavior. At low salt concentration and low electric fields, the proximal adsorption and the realignment follow the applied electric field, and the cosine of the water contact angle (WCA) follows a quadratic dependence on the applied electric field. At high salt concentration and high electric fields, the proximal adsorption saturates, which restricts further realignment and causes a saturation of the WCA. This case study provides physical insights into the much debated mechanism that underlies the contact angle saturation (CAS) found in macroscopic electrowetting phenomena and also provides an avenue for further studies of electrowetting at the atomic scale.

Molybdenum disulfide and water interaction parameters

Understanding the interaction between water and molybdenum disulfide (MoS₂) is of crucial importance to investigate the physics of various applications involving MoS₂ and water interfaces. An accurate force field is required to describe water and MoS₂ interactions. In this work, water-MoS₂ force field parameters are derived using the high-accuracy random phase approximation (RPA) method and validated by comparing to experiments. The parameters obtained from the RPA method result in water-MoS₂ interface properties (solid-liquid work of adhesion) in good comparison to the experimental measurements. An accurate description of MoS₂-water interaction will facilitate the study of MoS₂ in applications such as DNA sequencing, sea water desalination, and power generation.

A comparison between quantum chemistry and quantum Monte Carlo techniques for the adsorption of water on the (001) LiH surface

We present a comprehensive benchmark study of the adsorption energy of a single water molecule on the (001) LiH surface using periodic coupled cluster and quantum Monte Carlo theories. We benchmark and compare different implementations of quantum chemical wave function based theories in order to verify the reliability of the predicted adsorption energies and the employed approximations. Furthermore we compare the predicted adsorption energies to those obtained employing widely used van der Waals density-functionals. Our findings show that quantum chemical approaches are becoming a robust and reliable tool for condensed phase electronic structure calculations, providing an additional tool that can also help in potentially improving currently available van der Waals density-functionals.

Hexagonal boron nitride and water interaction parameters

The study of hexagonal boron nitride (hBN) in microfluidic and nanofluidic applications at the atomic level requires accurate force field parameters to describe the water-hBN interaction. In this work, we begin with benchmark quality first principles quantum Monte Carlo calculations on the interaction energy between water and hBN, which are used to validate random phase approximation (RPA) calculations. We then proceed with RPA to derive force field parameters, which are used to simulate water contact angle on bulk hBN, attaining a value within the experimental uncertainties. This paper demonstrates that end-to-end multiscale modeling, starting at detailed many-body quantum mechanics and ending with macroscopic properties, with the approximations controlled along the way, is feasible for these systems.

Strong Coupling between Nanofluidic Transport and Interfacial Chemistry: How Defect Reactivity Controls Liquid-Solid Friction through Hydrogen Bonding

Defects are inevitably present in nanofluidic systems, yet the role they play in nanofluidic transport remains poorly understood. Here, we report ab initio molecular dynamics (AIMD) simulations of the friction of liquid water on defective graphene and boron nitride sheets. We show that water dissociates at certain defects and that these "reactive" defects lead to much larger friction than the "nonreactive" defects at which water molecules remain intact. Furthermore, we find that friction is extremely sensitive to the chemical structure of reactive defects and to the number of hydrogen bonds they can partake in with the liquid. Finally, we discuss how the insight obtained from AIMD can be used to quantify the influence of defects on friction in nanofluidic devices for water treatment and sustainable energy harvesting. Overall, we provide new insight into the role of interfacial chemistry on nanofluidic transport in real, defective systems.