Using machine-learned potentials to better understand the CO₂-H₂O biphasic interface

Understanding how CO₂, a substance deeply relevant to the ongoing climate crisis, interacts with water can impact many applications. An example is carbon capture and storage techniques, in which CO₂ is captured and injected into aqueous storage sites, reducing its emissions into the atmosphere.

CO₂-H₂O can thus be described as one of the most important biphasic interfaces. Using machine-learned potentials, Brookes et al. performed molecular dynamics simulations to characterize the interfacial tension (IFT) profile of CO₂-H₂O to an ab initio level of accuracy.

“The IFT profile we obtained is crucial for understanding the macroscopic nature and miscibility of a biphasic fluid system,” said author Samuel Brookes. “Our approach, which utilizes state-of-the-art machine learning and enhanced sampling techniques, provides a blueprint for obtaining IFT estimates from the ground up.”

In addition to establishing a macroscopic view of CO₂-H₂O with IFTs, the authors explored the molecular structure of the interface. They found that at low pressures, the onset of reduced interfacial tensions coincides with the emergence of a liquid-like CO₂ monolayer. Furthermore, key differences between their improved CO₂-H₂O descriptions and classical results may have profound implications for our understanding of processes such CO₂ adsorption and its role in ocean acidification.

In the future, the authors plan to extend their work toward modeling other important CO₂-H₂O regimes.

“Following on from this work, we intend to ramp up the temperature and pressure of our simulations to replicate geological conditions,” said Brookes. “In doing this, we hope to gain insight into carbon transport processes deep under the Earth’s surface.”

Source: “The wetting of H₂O by CO₂,” by Samuel G. H. Brookes, Venkat Kapil, Christoph Schran, and Angelos Michaelides, Journal of Chemical Physics (2024). The article can be accessed at https://doi.org/10.1063/5.0224230 .

This paper is part of the Molecular Dynamics, Methods and Applications 60 Years after Rahman Collection, learn more here .