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Height-Driven Structure and Thermodynamic Property of Confined Ionic Liquids inside Carbon Nanochannel from the Molecular Dynamics Study

Abstract

Understanding the structural transition of ionic liquids (ILs) confined in nanospace is of great significance to the application of ILs in the process of energy storage, gas separation and other chemical engineering techniques. In this work, the quantitative relations between the properties and the height of nanochannel (H) for IL ([Emim]+[TF2N]-) are explored through the molecular dynamics simulations. Interestingly, the entropy of confined IL exhibits a nonmonotonic behavior as H increases: increasing firstly for H < 1.0 nm, then decreasing for 1.0 < H < 1.1nm, increasing again for H > 1.1 nm and finally approaching the liquid bulk IL. The vibrational spectrum of confined IL is analyzed to probe the nature of the nonmonotonic entropy, showing that the liquidity and partial solidity will be respectively attenuated and enhanced as H decreases from 5.0 to 0.75 nm. Besides, the hydrogen bonds (HBs) network and external force are also calculated, showing the similar nonmonotonic behavior compared with the thermodynamic properties. The entropy gain of confined IL should originate from the reduced hydrogen bonds interactions, weaker external force and partial solid nature, where more phase space sampling for IL inside bilayer graphene nanochannel (BLGC) can be reached. All the above relations demonstrate that there exists a critical height of nanochannel (HCR = 1.0 nm), where confined IL possesses a weaker hydrogen bonds interaction, higher entropy and stability. The critical height of the nanochannel is also identified in the analysis of the local structures of cation headgroups and anions, indicating that confined IL could have a faster in-plane diffusive ability. These factors can serve as key indicators in quantitatively characterizing the mechanism of structural transition of ILs inside nanochannel and benefit the rational design of nanopore and nanochannel to regulate the properties and structures of ILs in the practical application scenarios.

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Publication details

The article was received on 06 Feb 2019, accepted on 08 Apr 2019 and first published on 08 Apr 2019


Article type: Paper
DOI: 10.1039/C9CP00732F
Citation: Phys. Chem. Chem. Phys., 2019, Accepted Manuscript

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    Height-Driven Structure and Thermodynamic Property of Confined Ionic Liquids inside Carbon Nanochannel from the Molecular Dynamics Study

    C. Wang, Y. Wang, Y. LU, H. He, F. Huo, K. Dong, N. Wei and S. Zhang, Phys. Chem. Chem. Phys., 2019, Accepted Manuscript , DOI: 10.1039/C9CP00732F

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