The effect of n vs. iso isomerization on the thermophysical properties of aromatic and non-aromatic ionic liquids
authors Rodrigues, ASMC; Almeida, HFD; Freire, MG; Lopes-da-Silva, JA; Coutinho, JAP; Santos, LMNBF
nationality International
journal FLUID PHASE EQUILIBRIA
author keywords Ionic liquids; Density; Viscosity; Heat capacity; Refractive index; Surface tension; Glass transition; Phase behaviour; Imidazolium; Pyridinium; Piperidinium; Pyrrolidinium; Bis(trifluoromethylsulfonyl)imide; Differential scanning calorimetry; Isomerization
keywords ALKYL SIDE-CHAINS; THERMODYNAMIC PROPERTIES; HEAT-CAPACITY; SURFACE TENSIONS; PHYSICOCHEMICAL PROPERTIES; PHYSICAL-PROPERTIES; 1-BUTYL-1-METHYLPYRROLIDINIUM BIS(TRIFLUOROMETHYLSULFONYL)IMIDE; IMIDAZOLIUM; TEMPERATURE; CATION
abstract This work explores the n vs. iso isomerization effects on the physicochemical properties of different families of ionic liquids (ILs) with variable aromaticity and ring size. This study comprises the experimental measurements, in a wide temperature range, of the ILs' thermal behaviour, heat capacities, densities, refractive indices, surface tensions, and viscosities. The results here reported show that the presence of the iso-alkyl group leads to an increase of the temperature of the glass transition, T-g. The isopyrrolidinium (5 atoms ring cation core) and iso-piperidinium (6 atoms ring cation core) ILs present a strong differentiation in the enthalpy and entropy of melting. Non-aromatic ILs have higher molar heat capacities due to the increase of the atomic contribution, whereas it was not found any significant differentiation between then and iso-alkyl isomers. A small increase of the surface tension was observed for the non-aromatic Its, which could be related to their higher cohesive energy of the bulk, while the lower surface entropy observed for the iso isomers indicates a structural resemblance between the IL bulk and surface. The significant differentiation between ILs with a 5 and 6 atoms ring cation in the n-alkyl series (where 5 atoms ring cations have higher surface entropy) is an indication of a more efficient arrangement of the non-polar region at the surface in ILs with smaller cation cores. The ILs constituted by non aromatic piperidinium cation, and iso-alkyl isomers were found to be the most viscous among the studied Its due to their higher energy barriers for shear stress. (C) 2016 Published by Elsevier B.V.
publisher ELSEVIER SCIENCE BV
issn 0378-3812
year published 2016
volume 423
beginning page 190
ending page 202
digital object identifier (doi) 10.1016/j.fluid.2016.04.009
web of science category Thermodynamics; Chemistry, Physical; Engineering, Chemical
subject category Thermodynamics; Chemistry; Engineering
unique article identifier WOS:000378961800020
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journal analysis (jcr 2017):
journal impact factor 2.197
5 year journal impact factor 2.214
category normalized journal impact factor percentile 57.695
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