Controllable structure phases and tunable freezing zones of water confined in multi-walled carbon nanotube capillaries

Abstract

One-dimensional nanoconfined water exhibits rich structure phases. The freezing behavior of water confined in single-walled carbon nanotubes has been studied by both experimental measurements and theoretical simulations, however, it lacks of studying the freezing behavior of water confined in multi-walled carbon nanotubes (MWCNTs). Herein, we investigated the freezing behavior of water confined in MWCNTs using molecular dynamics simulations. Flat-square-walled ice nanotubes (FSW-INTs) were formed in the gaps with the inter-wall spacing of 6.66 Å, while, puckered-rhombic-walled ice nanotubes (PRW-INTs) were observed in the gaps with the inter-wall spacing of 8.61 Å. Then, the INT structures formed among the inter-wall gaps of MWCNTs can be controlled by tuning the inter-wall spacings of MWCNTs. Specifically, various groups of FSW-INTs and/or PRW-INTs were designed to form by using MWCNTs with the inter-wall spacing of 6.66 and/or 8.61 Å. In addition, it was found that water could be frozen in a simultaneous way or be frozen in a zone-by-zone form by tuning the inter-wall spacings of the MWCNTs due to the freezing temperatures of INTs are related with their diameters. The study will provide deep insights into the freezing behavior of water in MWCNTs.