Does twist angle affect the properties of water confined inside twisted bilayer graphene?

Graphene nanoslit pores are used for nanofluidic devices, such as, in water desalination, ion-selective channels, ionic transistors, sensing, molecular sieving, blue energy harvesting, and protein sequencing. It is a strenuous task to prepare nanofluidic devices, because a small misalignment leads to a significant alteration in various properties of the devices. Here, we focus on the rotational misalignment between two parallel graphene sheets. Using molecular dynamics simulation, we probe the structure and dynamics of monolayer water confined inside graphene nanochannels for a range of commensurate twist angles. With SPC/E and TIP4P/2005 water models, our simulations reveal the independence of the equilibrium number density-n similar to 13 nm(-2) for SPC/E and n similar to 11.5 nm(-2) for TIP4P/2005-across twists. Based on the respective densities of the water models, the structure and dielectric constant are invariant of twist angles. The confined water structure at this density shows square ice ordering for SPC/E water only. TIP4P/2005 shows ordering at the vicinity of a critical density (n similar to 12.5 nm(-2)). The average perpendicular dielectric constant of the confined water remains anomalously low (similar to 2 for SPC/E and similar to 6 for TIP4P/2005) for the studied twist angles. We find that the friction coefficient of confined water molecules varies for small twist angles, while becoming independent for twists greater than 5.1(?). Our results indicate that a small, angular misalignment will not impair the dielectric properties of monolayer water within a graphene slit-pore, but can significantly influence its dynamics.

Automated summary

Graphene nanoslit pores are used for various nanofluidic devices, and the rotational misalignment between two parallel graphene sheets can affect the properties of the devices. The structure and dielectric constant of confined water molecules remain unchanged for different twist angles, while the ordering of water molecules shows differences between SPC/E and TIP4P/2005 water models. The friction coefficient of the confined water molecules varies for small twist angles, but becomes independent for twists greater than 5.1°.