Tuneable interphase transitions in ionic liquid/carrier systems via voltage control

Sichao Li; Georgia A Pilkington; Filip Mehler; Oliver S Hammond; Anthony Boudier; Alexei Vorobiev; Sergei Glavatskih; Mark W Rutland

doi:10.1016/j.jcis.2023.08.111

Tuneable interphase transitions in ionic liquid/carrier systems via voltage control

J Colloid Interface Sci. 2023 Dec 15;652(Pt B):1240-1249. doi: 10.1016/j.jcis.2023.08.111. Epub 2023 Aug 19.

Authors

Sichao Li¹, Georgia A Pilkington¹, Filip Mehler¹, Oliver S Hammond², Anthony Boudier³, Alexei Vorobiev⁴, Sergei Glavatskih⁵, Mark W Rutland⁶

Affiliations

¹ Division of Surface and Corrosion Science, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
² Department of Materials and Environmental Chemistry, Stockholm University, SE-114 18 Stockholm, Sweden; Department of Biological and Chemical Engineering, Aarhus University, Aarhus C 8000 Denmark.
³ Department of Materials and Environmental Chemistry, Stockholm University, SE-114 18 Stockholm, Sweden.
⁴ Department of Physics and Astronomy, Division of Materials Physics, Uppsala University, SE-751 20 Uppsala, Sweden.
⁵ System and Component Design, Department of Engineering Design, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden; School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia; Department of Electromechanical, Systems and Metal Engineering, Ghent University, B-9052 Ghent, Belgium.
⁶ Division of Surface and Corrosion Science, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden; School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia; Bioeconomy and Health Department Materials and Surface Design, RISE Research Institutes of Sweden, SE-114 28 Stockholm, Sweden; Laboratoire de Tribologie et Dynamique des Systèmes, École Centrale de Lyon, 69134 Ecully Cedex, France. Electronic address: mark@kth.se.

PMID: 37657223
DOI: 10.1016/j.jcis.2023.08.111

Abstract

The structure and interaction of ionic liquids (ILs) influence their interfacial composition, and their arrangement (i.e., electric double-layer (EDL) structure), can be controlled by an electric field. Here, we employed a quartz crystal microbalance (QCM) to study the electrical response of two non-halogenated phosphonium orthoborate ILs, dissolved in a polar solvent at the interface. The response is influenced by the applied voltage, the structure of the ions, and the solvent polarizability. One IL showed anomalous electro-responsivity, suggesting a self-assembly bilayer structure of the IL cation at the gold interface, which transitions to a typical EDL structure at higher positive potential. Neutron reflectivity (NR) confirmed this interfacial structuring and compositional changes at the electrified gold surface. A cation-dominated self-assembly structure is observed for negative and neutral voltages, which abruptly transitions to an anion-rich interfacial layer at positive voltages. An interphase transition explains the electro-responsive behaviour of self-assembling IL/carrier systems, pertinent for ILs in advanced tribological and electrochemical contexts.

Keywords: Electric double-layer structure; Interfacial layers; Neutron reflectivity; Non-halogenated ionic liquids; Quartz crystal microbalance.