abstract
We have investigated, both theoretically and experimentally, the balance between the presence of alkyl and perfluoroalkyl side chains on the surface organization and surface tension of fluorinated ionic liquids (FILs). A series of ionic liquids (ILs) composed of 1-alkyl-3-methylimidazolium cations ([C(n)C(1)im] with n = 2, 4, 6, 8, 10, or 12) combined with the perfluorobutanesulfonate anion was used. The surface tensions of the investigated liquid salts are considerably lower than those reported for non fluorinated ionic liquids. The most surprising and striking feature is the identification, for the first time, of a minimum at n = 8 in the surface tension versus the length of the IL cation alkyl side chain. Supported by molecular dynamics (MD) simulations, it was found that this trend is a result of the competition between the two nonpolar domains (perfluorinated and aliphatic) pointing toward the gas-liquid interface, a phenomenon which occurs in ILs with perfluorinated anions. Furthermore, these ILs present the lowest surface entropy reported to date.
keywords
ORGANIC LIQUIDS; CHAIN-LENGTH; FORCE-FIELD; TEMPERATURE; DENSITY; ALKYL; BEHAVIOR; CATION; VISCOSITY; FORMATE
subject category
Chemistry; Materials Science
authors
Luis, A; Shimizu, K; Araujo, JMM; Carvalho, PJ; Lopes-da-Silva, JA; Lopes, JNC; Rebelo, LPN; Coutinho, JAP; Freire, MG; Pereiro, AB
our authors
Andreia Veríssimo Luís
Research Fellowship
Mara Guadalupe Freire Martins
Coordinating Researcher
Pedro J. Carvalho
Assistant ProfessorGroups
G4 - Renewable Materials and Circular Economy
G5 - Biomimetic, Biological and Living Materials
Projects
CICECO - Aveiro Institute of Materials (UID/CTM/50011/2013)
Igy Technology: A Purication Platform using Ionic-Liquid-Based Aqueous Biphasic Systems (IGYPURTECH)
acknowledgements
The authors wish to thank FCT/MEC (Portugal) for financial support through grants SFRH/BPD/82264/2011 (P.J.C.) and SFRH/BPD/94291/2013 (K.S.), contracts under Investigator FCT 2014 (A.B.P. and J.M.M.A.), and projects PTDC/QEQ-EPR/5841/2014, PTDC/QEQ-FTT/3289/2014, FCT-ANR/CTM-NAN/0135/2012, IF/00210/2014/CP1244/CT0003, UID/Multi/04551/2013, UID/QUI/00100/2013, and UID/CTM/50011/2013. M.G.F. acknowledges the European Research Council (ERC) for the Starting Grant ERC-2013-StG-337753. The NMR spectrometers are part of The National NMR Facility, supported by FCT/MEC (RECI/BBB-BQB/0230/2012).