Simulations of Pressurised Water Flow through Carbon Nanotubes
- PDF / 762,691 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 10 Downloads / 203 Views
1258-R10-07
Simulations of Pressurised Water Flow through Carbon Nanotubes
S. P. Shaw and D. A. Faux Advanced Technology Institute, University of Surrey, Guildford, Surrey, UK, GU2 7XH ABSTRACT Molecular dynamics simulations of the flow of pressurized water through carbon nanotubes of chirality (9,0), (12,0), (15,0) and (18,0) have been undertaken at 298K with a water density of approximately 1240kg/m3. Results show that the rate of filling is least in the smallest diameter nanotube, but that there is less variation in the time taken to reach maximum occupancy. The water molecules are found to undergo restructuring due to their confinement, with detailed molecular arrangement dependent on CNT diameter. Enhanced rates of flow are shown for the (15,0) nanotube, highlighting the effect of nanotube diameter on confinement and thus on flow. INTRODUCTION There has been considerable interest in the behaviour of water molecules within confined nano-sized spaces, for example, in the study of drug-delivery systems, cements, zeolites and polymeric materials. Water/carbon nanotubes (CNT) systems not only provide a relatively simple case study [1] but also have potential applications for fluid piping, desalination and drug delivery. A greater understanding of the properties of hydrated CNTs is required in order to establish the prospects of this novel system for commercial applications. This Paper reports the results of investigations into the pressurized flow of water through CNTs using molecular dynamics simulation. The initial stages of water ingress, water density within the tube, drift velocity and flow rate are studied for (9,0), (12,0), (15,0) and (18,0) nanotubes with diameters of 0.71, 0.95, 1.19 and 1.43nm respectively. COMPUTER SIMULATION Classical molecular dynamics (MD) simulations are used to investigate the flow of water molecules within the confined space of flexible single-walled CNTs. The simulation cell, illustrated in Figure 1, consists of four CNTs about 7.5nm in length in a bundle and placed adjacent to a bath of water molecules. Periodic boundary conditions are imposed in the x- and ydirections with a wall of ‘frozen’ atoms acting as a barrier in the z-direction to prevent molecules from entering the nanotube from the opposite end. A large number of potential functions exist to model the water-water interactions, ranging from simple, rigid models to more sophisticated potentials involving flexible molecules with additional charge sites. The size and duration timescales required for most simulations restricts the degree of complexity that is computationally feasible. Since this work looks to examine the flow characteristics of water, a rigid model such as single-point charge (SPC) [2] and TIP3P [3] were rejected in favour of greater flexibility. The flexible single point charge (SPC/FW) model of Wu et al [4] is used to model the water-water interaction. It is based on SPC, but allows
flexibility of bond length and bond angle. The SPC/FW model yields an excellent value for the diffusion coefficient (2.32
Data Loading...
