Diffusion of Water Molecules in Narrow Carbon Nanotubes and Nanorings

Introduction: It is known that fluids confined in nanometric spaces behave very differently from their bulk counterpart [1]. Lately, the process of transport of confined water through narrow channels has attracted a lot of attention, since knowledge of these processes is important in understanding transport through ion channels [2]. Numerical studies by Lee et al. [3] and Mao et al. [4] of the diffusion of oxygen and methane molecules, respectively, through narrow carbon nanotubes suggest the occurrence of single file diffusion. However in all these simulations, the time over which the mean squared displacement (MSD) is measured is rather short (100-500 ps). Additionally, due to finite size effects (the consequences of which are elucidated in the present work), it is difficult to draw a firm conclusion about the true nature of diffusion of these molecules inside the nanotube. The goal of our study is to develop a better understanding of the nature of diffusion of water molecules in narrow carbon nanotubes.