The Influence of the Rigidity of a Carbon Nanotube on the Structure and Dynamics of Confined Methanol

In this paper, we compare the behavior of liquid methanol confined by an open-ended single-walled nanotube (SWCNT) under four different simulation conditions by using the molecular dynamics (MD) simulations technique. The first model is a rigid and fixed SWCNT with all its carbon atoms fixed at their initial positions; the second is a flexible and fixed SWCNT with its centre-of-mass fixed at the center of the MD box and with the carbon–carbon bond potential applied; the third is a rigid and floating SWCNT, and the fourth is the most realistic flexible and floating SWCNT model — without fixed atoms and with bond potential. The microscopic structure and transport properties of bulk methanol confined by the four different SWCNTs were analyzed. No changes in the radial distribution functions of the hydrogen bond between MeOH molecules are found, and the self-diffusion constant and microscopic dipole relaxation time are essentially unaffected by the confinements. In spite of the flexible/rigid or fixed/floating ð15; 15Þ SWCNT model used, the structure and transport properties of confined MeOH are found to be very close in all the simulated cases. We conclude that using the approximation of rigid or/and fixed SWCNT does not lead to any systematic errors in properties of the confined liquid. The results show that simulations using rigid carbon nanotubes provide a reliable description of molecular diffusion and other solvent properties in a variety of applications, such electro-chemical devices, membranes and sensors that rely on these properties.