Adsorption of an alkane mixture on carbon nanotubes: Selectivity and kinetics

Abstract

Adsorption and its dynamical process of polymer mixtures consisting of long and short alkane molecules around a carbon nanotube ͑CNT͒ are studied with molecular-dynamics ͑MD͒ simulations and master equation. Preferred adsorption is found for long chained molecules compared to short ones, due to favorable interfacial interaction energies of the former with the tube. A dominating ratio ϳ32 is calculated for the adsorption sites of hectane molecules vs decane molecules in their equal weight melt mixture when around a CNT ͑5, 5͒ at 420 K. The adsorption-desorption kinetics of the molecules is described through a master equation in combination with MD simulations. A fully adsorbed alkane molecule is found to be much more stable than a partially adsorbed one, regarding its monomer desorption rate from the nanotube. This results in a sharp peak in the population of the morphology of the adsorbed molecules at their maximum bound fraction f b = 1. The crystallization in the mixture composite and the selectivity and molecule morphology during a cooling process were also discussed.

Organization of polymer chains onto long, single-wall carbon nano-tubes: Effect of tube diameter and cooling method

“…Our MD model is very similar to recent works by Tallury and Pasquinelli, 25,26 Yang, 27 and Wei. [30][31][32] Most importantly we allow for the possibility of epitaxial alignment between the SWCNT and the polymer by individually modelling the beads which make up both the SWCNT and polymer chain. A SWCNT consists of a network of hexagonally orientated carbon atoms.…”

“…They predominantly found a helical organization of polymer chains on nano-tubes of different diameters. Wei [30][31][32] implemented molecular dynamics simulations to consider the conformations of polyethylene chains on CNTs. Wei 30 found the wrapping angle of the polymer on the cylindrical nanotube varied from zero degrees (aligned with CNT axis) on smaller radius tubes to larger angles for larger radius tubes.…”

Monte Carlo Simulations of Thin Hydrocarbon Films: Composition Heterogeneity and Structure at the Solid–Liquid and Liquid–Vapor Interfaces

“…23,30,35 Preferential adsorption at the liquid−solid interface is seen in a variety of mixtures. 1,10,14,[19][20][21][22][23][24][25][26]33 A few experimental studies of linear alkane mixtures indicate that longer alkanes are preferentially adsorbed onto graphite, even when the chains differ by only one methylene unit. 1,[19][20][21][22]25,32 Castro et al examined a variety of binary mixtures of linear alkanes adsorbed on graphite near the bulk melting point using differential scanning calorimetry and incoherent elastic neutron scattering.…”

“…Understanding the properties of liquid films of articulated molecules near solid surfaces is of interest for many diverse applications, including lubrication, adhesion, and chromatography. The formation of molecular layers in liquids near solid substrates is a well-documented phenomenon. − The structural and dynamic properties within these layers differ from the bulk liquid. For example, the viscosity is generally higher within the layers than in the bulk. ,, …”

“…Preferential adsorption at the liquid–solid interface is seen in a variety of mixtures. ,,,− , A few experimental studies of linear alkane mixtures indicate that longer alkanes are preferentially adsorbed onto graphite, even when the chains differ by only one methylene unit. ,− ,, Castro et al examined a variety of binary mixtures of linear alkanes adsorbed on graphite near the bulk melting point using differential scanning calorimetry and incoherent elastic neutron scattering. − At temperatures slightly above the bulk melting point, these studies indicate the formation of a solid monolayer next to the substrate when either pure liquids or mixtures are adsorbed. In mixtures, the longer component is preferentially adsorbed at the interface, even when it is the minor component .…”