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Molecular Architecture Effects on Bulk Nanostructure in Bis(Orthoborate) Ionic Liquids |
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| Authors: | Oliver S Hammond Guillaume Bousrez Filip Mehler Sichao Li Manishkumar R Shimpi James Doutch Leide Cavalcanti Sergei Glavatskih Oleg N Antzutkin Mark W Rutland Anja-Verena Mudring |
| Affiliation: | 1. Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, SE-114 18 Sweden
Department of Biological and Chemical Engineering and iNANO, Aarhus University, Aarhus C, 8000 Denmark;2. Division of Surface and Corrosion Science, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, SE-100 40 Sweden;3. Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, SE-114 18 Sweden Chemistry of Interfaces, Luleå University of Technology, Luleå, SE-971 87 Sweden;4. ISIS Neutron & Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell-Oxford, OX11 0QX UK;5. Department of Engineering Design, KTH Royal Institute of Technology, Stockholm, SE-10044 Sweden School of Chemistry, University of New South Wales, Sydney, 2052 Australia Department of Electromechanical, Systems and Metal Engineering, Ghent University, Ghent, B-9052 Belgium;6. Chemistry of Interfaces, Luleå University of Technology, Luleå, SE-971 87 Sweden;7. Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, SE-114 18 Sweden |
| Abstract: | A series of 19 ionic liquids (ILs) based on phosphonium and imidazolium cations of varying alkyl-chain lengths with the orthoborate anions bis(oxalato)borate BOB]−, bis(mandelato)borate, BMB]− and bis(salicylato)borate, BScB]−, are synthesized and studied using small-angle neutron scattering (SANS). All measured systems display nanostructuring, with 1-methyl-3-n-alkyl imidazolium-orthoborates forming clearly bicontinuous L3 spongelike phases when the alkyl chains are longer than C6 (hexyl). L3 phases are fitted using the Teubner and Strey model, and diffusely-nanostructured systems are primarily fitted using the Ornstein-Zernicke correlation length model. Strongly-nanostructured systems have a strong dependence on the cation, with molecular architecture variation explored to determine the driving forces for self-assembly. The ability to form well-defined complex phases is effectively extinguished in several ways: methylation of the most acidic imidazolium ring proton, replacing the imidazolium 3-methyl group with a longer hydrocarbon chain, substitution of BOB]− by BMB]−, or exchanging the imidazolium for phosphonium systems, irrespective of phosphonium architecture. The results suggest there is only a small window of opportunity, in terms of molecular amphiphilicity and cation:anion volume matching, for the formation of stable extensive bicontinuous domains in pure bulk orthoborate-based ILs. Particularly important for self-assembly processes appear to be the ability to form H-bonding networks, which offer additional versatility in imidazolium systems. |
| Keywords: | ionic liquids nanostructures orthoborates small angle neutron scattering |