Anion Architecture Controls Structure and Electroresponsivity of Anhalogenous Ionic Liquids in a Sustainable Fluid

Sichao Li; Oliver S Hammond; Andrew Nelson; Liliana de Campo; Michael Moir; Carl Recsei; Manishkumar R Shimpi; Sergei Glavatskih; Georgia A Pilkington; Anja-Verena Mudring; Mark W Rutland

doi:10.1021/acs.jpcb.3c08189

Anion Architecture Controls Structure and Electroresponsivity of Anhalogenous Ionic Liquids in a Sustainable Fluid

J Phys Chem B. 2024 May 2;128(17):4231-4242. doi: 10.1021/acs.jpcb.3c08189. Epub 2024 Apr 19.

Authors

Sichao Li¹, Oliver S Hammond^{2

3}, Andrew Nelson⁴, Liliana de Campo⁴, Michael Moir⁵, Carl Recsei⁵, Manishkumar R Shimpi^{2

6}, Sergei Glavatskih^{7

8

9}, Georgia A Pilkington¹, Anja-Verena Mudring^{2

3

10}, Mark W Rutland^{1

8

11

12}

Affiliations

¹ Division of Surface and Corrosion Science, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden.
² Department of Materials and Environmental Chemistry, Stockholm University, Stockholm SE-114 18, Sweden.
³ intelligent Advanced Materials, Department of Biological & Chemical Engineering and iNANO, Aarhus University, Aarhus C 8000, Denmark.
⁴ Australian Centre for Neutron Scattering, ANSTO, Lucas Heights, New South Wales 2234, Australia.
⁵ National Deuteration Facility, ANSTO, Lucas Heights, New South Wales 2234, Australia.
⁶ Chemistry of Interfaces, Department of Civil and Environmental Engineering, Luleå University of Technology, Luleå SE-97187, Sweden.
⁷ System and Component Design, Department of Engineering Design, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden.
⁸ School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia.
⁹ Department of Electromechanical, Systems and Metal Engineering, Ghent University, Ghent B-9052, Belgium.
¹⁰ Department of Physics, Umeå University, Umeå SE-901 87, Sweden.
¹¹ Bioeconomy and Health Department Materials and Surface Design, RISE Research Institutes of Sweden, Stockholm SE-114 28, Sweden.
¹² Laboratoire de Tribologie et Dynamique des Systèmes, École Centrale de Lyon, Ecully Cedex 69134, France.

Abstract

Three nonhalogenated ionic liquids (ILs) dissolved in 2-ethylhexyl laurate (2-EHL), a biodegradable oil, are investigated in terms of their bulk and electro-interfacial nanoscale structures using small-angle neutron scattering (SANS) and neutron reflectivity (NR). The ILs share the same trihexyl(tetradecyl)phosphonium ([P_6,6,6,14]⁺) cation paired with different anions, bis(mandelato)borate ([BMB]^-), bis(oxalato)borate ([BOB]^-), and bis(salicylato)borate ([BScB]^-). SANS shows a high aspect ratio tubular self-assembly structure characterized by an IL core of alternating cations and anions with a 2-EHL-rich shell or corona in the bulk, the geometry of which depends upon the anion structure and concentration. NR also reveals a solvent-rich interfacial corona layer. Their electro-responsive behavior, pertaining to the structuring and composition of the interfacial layers, is also influenced by the anion identity. [P_6,6,6,14][BOB] exhibits distinct electroresponsiveness to applied potentials, suggesting an ion exchange behavior from cation-dominated to anion-rich. Conversely, [P_6,6,6,14][BMB] and [P_6,6,6,14][BScB] demonstrate minimal electroresponses across all studied potentials, related to their different dissociative and diffusive behavior. A mixed system is dominated by the least soluble IL but exhibits an increase in disorder. This work reveals the subtlety of anion architecture in tuning bulk and electro-interfacial properties, offering valuable molecular insights for deploying nonhalogenated ILs as additives in biodegradable lubricants and supercapacitors.