Two-length scale description of hydrophobic room-temperature ionic liquid-alcohol systems

In pure hydrophobic 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C(n)C(m)im][TFSI] (2 <= n <= 10, m = 1), the crossover alkyl side-chain length of the C(n)C(1)m(+) cation (n(c)) is found to be equal to 6 by a simultaneous X-ray diffraction and differential scanning calorimetry. By adding butanol, a geometrical factor of butanol isomers became dominant in the liquid-liquid phase equilibrium (LLE) above n(c). In the LLE of [C(n)C(1)im][TFSI]-butanol, upper critical solution temperatures (T-UCST) and critical concentration (x(c)) at the top of the phase separation depended extensively on n and the butanol isomer effect In primary alcohol (ClH2l+OH), the alkyl chain length of alcohols, l, enables it to increase the T-UCST at a fixed n. Density at T-UCST and x(c) have the opposite tendency in the two-length scale (n and l). In Raman spectroscopy, the conformation ratio of the TFSI- anion as an instability factor of liquid mixing exhibits an anomaly in the vicinity of n(c). (C) 2015 Elsevier B.V. All rights reserved.