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The surface tension of nine tricyanomethanide (C(CN)3−)- and tetracyanoborate (B(CN)4−)-based ionic liquids (ILs) carrying a homologous series of the 1-alkyl-3-methylimidazolium (alkyl-MIM+) cations EMIM+ (ethyl), BMIM+ (butyl), HMIM+ (hexyl), OMIM+ (octyl), and DMIM+ (decyl) was measured with the pendant drop method in the temperature range between (283 and 353) K at atmospheric pressure with an estimated uncertainty of 2 % (k = 2). For the probed ILs, the surface tension decreases with increasing temperature and increasing alkyl chain length of the cation. Smaller values for the B(CN)4−-based ILs compared to the C(CN)3−-based ILs having the same cation were observed. The measured surface tensions agree with the limited number of experimental data found in the literature for the two IL families. A simple prediction based on the surface tension measured at 293 K and the temperature dependence of density showed good agreement with the measured temperature-dependent data. In comparison to other alkyl-MIM+-based ILs with anions of varying molecular size, the fairly large surface tensions of the ILs investigated in this study could be attributed to the strong charge delocalization in their relatively small anions.
Koller et al. (Thu,) studied this question.