Abstract
Over the past decade many works have focused on various aspects of the dynamics of liquids confined at the nanoscale such as e.g. water flow enhancement through carbon nanotubes (CNTs). Transport of room temperature ionic liquids (RTILs) through various nanochannels has also been explored and some conflicting findings about their translational dynamics have been reported. In this work, we focus on translational dynamics of RTILs confined in various CNTs. By means of molecular dynamics simulations we highlight a substantially enhanced diffusion of confined RTILs with an increase up to two orders of magnitude with respect to bulk-phase properties. This ultrafast diffusion of RTILs inside CNTs is shown to result from the combination of various factors such as low friction, molecular stacking, size, helicity, curvature and cooperative dynamics effects.
Highlights
Several numerical and theoretical works have focused on room temperature ionic liquids (RTILs) confined into cylindrical nanopores, such as CNTs14,16–22 or silica materials[23,24,25], and slit-like pores such as rutile slabs[26] or graphitic pores[13]
[Omim+][BF−4 ] mobility induced in CNTs33.It is worth noting found in very good agreement with experiments[23,31,34] and faster that bulk values inferred translational dynamics of from simulations were [C4mim+] with respect to [Tf2N−] in the bulk phase[34,35] was well reproduced by molecular dynamics (MD) simulations
Based on previous findings on low friction of confined water within CNTs37,38,41,42 we first tried to correlate the fast diffusion of RTILs confined in carbon nanotubes (CNTs) with low friction
Summary
Several numerical and theoretical works have focused on RTILs confined into cylindrical nanopores, such as CNTs14,16–22 or silica materials[23,24,25], and slit-like pores such as rutile slabs[26] or graphitic pores[13] Results from these studies suggest that both local RTIL structure and local dynamics of confined cations and anions are very complex and heterogeneous, depending strongly on the distance between ions and the pore wall. In addition to their tremendous physical properties, CNTs represent models of hydrophobic nanopores enabling to explore ultraconfinement effects on local structure and dynamics of liquids. Force fields and computational procedure are detailed in the Method Section. [C8isoq+][Tf2N−] and [Me3BuN+] [Tf2N−] were chosen so as to investigate the impact of aromatic rings on RTIL translational dynamics
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