The unique properties of aqueous electrolytes in ultrathin nanopores have drawn a great deal of attention in a variety of applications, such as power generation, water desalination, and disease diagnosis. Inside the nanopore, at the interface, properties of ions differ from those predicted by the classical ionic layering models (e.g., Gouy–Chapman electric double layer) when the thickness of the nanopore approaches the size of a single atom (e.g., nanopores in a single-layer graphene membrane). Here, using extensive molecular dynamics simulations, the structure and dynamics of aqueous ions inside nanopores are studied for different thicknesses, diameters, and surface charge densities of carbon-based nanopores [ultrathin graphene and finite-thickness carbon nanotubes (CNTs)]. The ion concentration and diffusion coefficient in ultrathin nanopores show no indication of the formation of a Stern layer (an immobile counter-ionic layer) as the counter-ions and nanopore atoms are weakly correlated in time compared to the strong correlation observed in thick nanopores. The weak correlation observed in ultrathin nanopores is indicative of a weak adsorption of counter-ions onto the surface compared to that of thick pores. The vanishing counter-ion adsorption (ion–wall correlation) in ultrathin nanopores leads to several orders of magnitude shorter ionic residence times (picoseconds) compared to the residence times in thick CNTs (seconds). The results of this study will help better understand the structure and dynamics of aqueous ions in ultrathin nanopores.
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7 April 2021
Research Article|
April 01 2021
Dynamic and weak electric double layers in ultrathin nanopores
Special Collection:
Fluids in Nanopores
Mohammad Heiranian
;
Mohammad Heiranian
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign
, Urbana, Illinois 61801, USA
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Yechan Noh;
Yechan Noh
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign
, Urbana, Illinois 61801, USA
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Narayana R. Aluru
Narayana R. Aluru
a)
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign
, Urbana, Illinois 61801, USA
a)Author to whom correspondence should be addressed: aluru@illinois.edu. URL: http://aluru.mechse.illinois.edu/
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a)Author to whom correspondence should be addressed: aluru@illinois.edu. URL: http://aluru.mechse.illinois.edu/
Note: This paper is part of the JCP Special Topic on Fluids in Nanopores.
J. Chem. Phys. 154, 134703 (2021)
Article history
Received:
February 18 2021
Accepted:
March 03 2021
Citation
Mohammad Heiranian, Yechan Noh, Narayana R. Aluru; Dynamic and weak electric double layers in ultrathin nanopores. J. Chem. Phys. 7 April 2021; 154 (13): 134703. https://doi.org/10.1063/5.0048011
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