Re-entrant Phase Transitions and Dynamics of a Nanoconfined Ionic Liquid

Abstract

Ionic liquids constrained at interfaces or restricted in subnanometric pores are increasingly employed in modern technologies, including energy applications. Understanding the details of their behavior in these conditions is therefore critical. By using molecular dynamics simulation, we clarify theoretically and numerically the effect of confinement at the nanoscale on the static and dynamic properties of an ionic liquid. In particular, we focus on the interplay among the size of the ions, the slit pore width, and the length scale associated to the long-range organization of polar and apolar domains present in the bulk material. By modulating both the temperature and the extent of the confinement, we demonstrate the existence of a complex reentrant phase behavior, including isotropic liquid and liquid-crystal-like phases with different symmetries. We show how these changes impact the relative organization of the ions, with substantial modifications of the Coulombic ordering, and their dynamical state. In this respect, we reveal a remarkable decoupling of the dynamics of the counterions, pointing to very different roles played by these in charge transport under confinement. We finally discuss our findings in connection with very recent experimental and theoretical work.

Superionic liquids in conducting nanoslits: A variety of phase transitions and ensuing charging behavior

“…However, if the double layers on the opposite sides of the pores overlap, or if the pores are so narrow that they can accommodate only one layer of ions, then the physics and the laws of charge storage become different [3][4][5][6]. The need to maximize the capacitance and energy storage motivates the use of electrodes with such fine porosity, and, since the modern nanotechnology allows one to build well-defined nanoporous structures [7][8][9][10][11][12][13], understanding the laws of charge storage in nano-sized pores has become in great demand [6,[14][15][16][17][18][19][20][21].…”

A Highly Conductive Gel Polymer Electrolyte for Li–Mg Hybrid Batteries

“…IL-based materials have become extremely popular in recent years as electrolytes for Li-ion and various other batteries as well as for other applications which require ionic conductivity. ,,,,,, Although bulk ionic conductivity in ILs has been the subject of many recent studies, ,− charge transport is rarely interrogated in the context of a polymer ion gel, particularly in multicomponent mixtures containing metal ions. ILs have recently been shown to form ordered phases at interfaces and in confined pores, affecting free charge content, the dielectric environment, and implicitly the stability of the surrounding materials such as polar polymer phases and metal surfaces. − Thus, the fundamental properties and dynamics of IL mixtures in many contexts are not well understood, even as they become a cornerstone of many next-generation technologies.…”

Investigation of Dynamic Behavior of Confined Ionic Liquid [BMIM]+[TCM]− in Silica Material SBA-15 Using NMR

“…From the experimental point of view, the dynamical properties of many ILs have been investigated with several techniques, such as dielectric spectroscopy [ 19 , 20 ], neutron scattering [ 21 , 22 , 23 , 24 ], light scattering [ 19 ], and NMR spectroscopy [ 17 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. Theoretical studies using Molecular Dynamics (MD) simulations also reveal complex phase transitions of nano-confined ILs [ 32 , 33 , 34 ]. We refer readers to Ref.…”