Article,
Anion Architecture Controls Structure and Electroresponsivity of Anhalogenous Ionic Liquids in a Sustainable Fluid
Affiliations
- [1] KTH Royal Inst Technol, Dept Engn Design, Syst & Component Design, SE-10044 Stockholm, Sweden [NORA names: Sweden; Europe, EU; Nordic; OECD];
- [2] Aarhus Univ, Dept Biol & Chem Engn & iNANO, Intelligent Adv Mat, DK-8000 Aarhus, Denmark [NORA names: AU Aarhus University; University; Denmark; Europe, EU; Nordic; OECD];
- [3] Stockholm Univ, Dept Mat & Environm Chem, SE-11418 Stockholm, Sweden [NORA names: Sweden; Europe, EU; Nordic; OECD];
- [4] ANSTO, Australian Ctr Neutron Scattering, Lucas Heights, NSW 2234, Australia [NORA names: Australia; Oceania; OECD];
- [5] Lulea Univ Technol, Dept Civil & Environm Engn, Chem Interfaces, SE-97187 Lulea, Sweden [NORA names: Sweden; Europe, EU; Nordic; OECD];
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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,P-6,P-6,P-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,P-6,P-6,P-14][BOB] exhibits distinct electroresponsiveness to applied potentials, suggesting an ion exchange behavior from cation-dominated to anion-rich. Conversely, [P-6,P-6,P-6,P-14][BMB] and [P-6,P-6,P-6,P-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.