Effect of Alkyl Chains of Cation and Anion on the Thermophysical Properties of Propanenitrile imidazolium-Based Ionic Liquids

dioctylsulfosuccinate [C2CN Cnim]DOSS , dodecylsulfate [C2CN Cnim]DDS, benzene sulfonic acid
[C2CN Cnim]SBA, benzene sulfonate [C2CN Cnim]BS and trifluoromethanesulfonate [C2CN
Cnim]TFMS have been prepared. The present ionic liquids (ILs) are characterised using NMR,
FTIR and elemental analysis and their physical properties such as density, viscosity and refractive
index have been performed at a broad range of temperature (293.15 to 353.15) K and at atmospheric
pressure while their thermal stability were measured at heating rate 5 °C/min. The present ILs show
lower densities and higher viscosities compared to those of analogous nitrile-functionalized ILs
with different anions. The differences in these two properties are due to the presence of large anions
(low ion mobility), long alkyl chain of the cations (Van der Waals interactions) and hydrogen
bonding of the functional groups. The refractive index values of the present ILs are found to
increase after the incorporation of nitrile group and are in good agreement with that reported for
other imidazolium-based nitrile functionalized ILs The results show that thermal stability of the ILs
with DOSS, DDS, SBA, BS and TFMS anions were high in comparison with the corresponding ILs
with bromide anion. The coefficients of thermal expansion, lattice energy and molar refraction were
estimated from the experimental values of density and refractive index. These ILs show a weak
temperature dependency on the thermal expansion coefficient and low lattice energy.