Ion specific hydration in nano-confined electrical double layers

Z Zachariah; R M Espinosa-Marzal; M P Heuberger

doi:10.1016/j.jcis.2017.07.039

Ion specific hydration in nano-confined electrical double layers

J Colloid Interface Sci. 2017 Nov 15:506:263-270. doi: 10.1016/j.jcis.2017.07.039. Epub 2017 Jul 14.

Authors

Z Zachariah¹, R M Espinosa-Marzal², M P Heuberger³

Affiliations

¹ Laboratory for Surface Science and Technology, Department of Materials, ETH Zürich, Switzerland; Laboratory for Advanced Fibers, Empa Materials Science & Technology, St. Gallen, Switzerland.
² Laboratory for Surface Science and Technology, Department of Materials, ETH Zürich, Switzerland; Laboratory for Smart Interfaces in Environmental Nanotechnology, Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, IL, USA.
³ Laboratory for Surface Science and Technology, Department of Materials, ETH Zürich, Switzerland; Laboratory for Advanced Fibers, Empa Materials Science & Technology, St. Gallen, Switzerland. Electronic address: manfred.heuberger@empa.ch.

PMID: 28735200
DOI: 10.1016/j.jcis.2017.07.039

Abstract

We probe counter-ion specific effects in nano-confined electrical-double-layers (EDLs) by means of direct force measurements across a model slit pore in the extended surface forces apparatus. By variation of solution composition, we compare four different counter-ions with dissimilar hydration properties, namely Na⁺, K⁺, Cs⁺ as well as H₃O⁺, all confined between (001) mica surfaces. We discuss the results in terms of a recently proposed π-transition model, evoking hydrated ion layering as the recurrent structural element in highly confined EDLs. We demonstrate that the π-transition essentially proceeds in multiple steps in coherence with the event of single- or multiple- hydrated-ion layering.

Keywords: Confinement; Electrical double layer; Hydration; Ion specificity.