Effects of Electrostatic Interaction and Chirality on the Friction Coefficient of Water Flow Inside Single-Walled Carbon Nanotubes and Boron Nitride Nanotubes

Abstract

Water transport through carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) has attracted great scientific interest because of their potential applications in water purification and energy conversion. Recent experiments show surprising differences of the water flow friction coefficients in these two types of nanotubes with similar diameters, but the mechanism is yet to be fully understood. We use molecular dynamic simulations to model the transport process of water molecules inside CNTs and BNNTs, and the friction coefficients are calculated by the Green–Kubo formula. Our results show that at similar diameters, water molecules have smaller friction coefficients in zigzag CNTs than in zigzag BNNTs. By analyzing the potential energy landscape inside these nanotubes, we find that in CNTs, the lack of partial charges, and thus the absence of electrostatic interactions with water molecules, leads to a much smoother potential energy landscape and thus smaller water friction coefficient. Although partial charges in armchair BNNTs also lead to electrostatic interactions with water, the atomic arrangement in armchair nanotubes does not create local potential energy traps, and thus the friction coefficient is smaller than the zigzag counterparts. The result helps us understand the distinct behaviors of water flowing through CNTs and BNNTs.