Structure and Dynamics of Water Confined in Single-Wall Nanotubes

Abstract

The structure and dynamics of water confined in model single-wall carbon- and boron-nitride nanotubes (called SWCNT and SWBNNT, respectively) of different diameters have been investigated by molecular dynamics (MD) simulations at room temperature. The simulations were performed on periodically extended nanotubes filled with an amount of water that was determined by soaking a section of the nanotube in a water box in an NpT simulation (1 atm, 298 K). All MD production simulations were performed in the canonical (NVT) ensemble at a temperature of 298 K. Water was described by the extended simple point charge (SPC/E) model. The wall-water interactions were varied, within reasonable limits, to study the effect of a modified hydrophobicity of the pore walls. We report distribution functions for the water in the tubes in spherical and cylindrical coordinates and then look at the single-molecule dynamics, in particular self-diffusion. While this motion is slowed down in narrow tubes, in keeping with previous findings (Liu et al. J. Chem. Phys. 2005, 123, 234701-234707; Liu and Wang. Phys. Rev. 2005, 72, 085420/1-085420/4; Liu et al. Langmuir 2005, 21, 12025-12030) bulk-water like self-diffusion coefficients are found in wider tubes, more or less independently of the wall-water interaction. There may, however, be an anomaly in the self-diffusion for the SWBNNT.

Molecular Modeling and Mechanics of Acrylic Adhesives on a Graphene Substrate with Roughness

“…2g), as the first density peak corresponds to an H bond density that is more than four times than that of its bulk state. The singularity of mass and H bond distributions agrees with what has been observed for water at the interfaces with other nanomaterials [29][30][31][32]. In previous studies, it has been shown that a graphene substrate can lead to crystallization of polymer at the interface [33,34] and thus yields enhanced mechanics at the interface [35].…”

Diffusion enhancement in core-softened fluid confined in nanotubes

“…In all analyzed cases layering is observed. Axial layers are also observed in simulations for the SPC/E and TIP4P-EW models for water confined in nanotubes 5,38,46,55,58 . In the last cases, the presence of layering is attributed to the hydrogen bonds and surface effects.…”

“…At a * = a * c = 2.0 the diffusion reaches a minimum and the system assumes a crystal-like configuration as illustrated in Figure 8. Therefore, the confinement leads the fluid to a solidlike state, even at values of temperature and pressure far from solid state phase 5,38,41,51,55 .…”

“…Some simulations show a monotonical decrease of D with decreasing nanotube radius [54][55][56] while other simulations indicate the presence of a minimum 38,[47][48][49] . It has been suggested that the length of the nanotube and the length of the simulation would be responsible for the different results 3,57,58 and that friction should play also a relevant role 59 .…”

Nanoconfinement induced anomalous water diffusion inside carbon nanotubes

“…In the bulk phase, the water molecules diffuse as the Fickian type in which the mean square displacement (MSD) linearly scales with the time (Striolo 2006;Mashl et al 2003). While for the water confined in CNTs, the diffusion behavior becomes extraordinary due to the nanoscale confinement (Chen Q et al 2010;Das et al 2010;Devi et al 2010;Liu et al 2005a, b;Mashl et al 2003;Mukherjee et al 2010;Nanok et al 2009;Striolo 2006). Inside the (6, 6) CNT, the water molecules are organized in a chain-like structure in which they move simultaneously and cannot pass each other (Hummer et al 2001).…”