The effect of n vs. iso isomerization on the thermophysical properties of aromatic and non-aromatic ionic liquids

• Type: Article in International Scientific Journal
• Date: 2016

Authors

Rodrigues, ASMC (Author) Other; Almeida, HFD (Author) Other; Freire, MG (Author) Other; Lopes da Silva, JA (Author) Other; Coutinho, JAP (Author) Other; Luis M N B F Santos (Author) FCUP

Journal

Title: Fluid Phase Equilibria

Vol. 423

Pages: 190-202

ISSN: 0378-3812

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 28 Citations

Scopus - 31 Citations

Other information

Authenticus ID: P-00K-EWE

DOI: 10.1016/j.fluid.2016.04.009

Abstract (EN): 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.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 13