A Raman spectroscopy and rheology study of the phase transitions of the ionic liquid choline acetate

Melting of the ionic liquid choline acetate, [Chol][Ac], at similar to 335 K is manifest in the differential scanning calorimetry (DSC) curve as a broad band covering similar to 30 K of temperature range. The events taking place in the pre-melting of [Chol][Ac] are revealed by Raman spectroscopy and rheological measurements. The low-frequency range of the Raman spectrum exhibits changes in the intermolecular vibrational modes and the higher frequency range indicates conformational changes of the choline cation. Oscillatory rheological measurements show that the sample experiences a stiffening of its rheological characteristics within the temperature interval encompassing the melting process. Taking together the spectroscopic and rheological data, it is concluded that the sample experiences partial recrystallization during the pre-melting of [Chol][Ac]. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The melting behavior of the ionic liquid choline acetate, [Chol][Ac], was studied using differential scanning calorimetry, Raman spectroscopy, and rheological measurements. The results showed changes in intermolecular vibrational modes and conformational changes of the choline cation during the pre-melting process, leading to the conclusion that the sample experienced partial recrystallization.